| Doc. no. | N2729=08-0239 |
| Date: | 2008-08-24 |
| Project: | Programming Language C++ |
| Reply to: | Howard Hinnant <howard.hinnant@gmail.com> |
Reference ISO/IEC IS 14882:1998(E)
Also see:
This document contains only library issues which have been closed by the Library Working Group as duplicates or not defects. That is, issues which have a status of Dup or NAD. See the Library Active Issues List active issues and more information. See the Library Defect Reports List for issues considered defects. The introductory material in that document also applies to this document.
Section: D.9.1.3 [auto.ptr.conv] Status: NAD Submitter: Nathan Myers Date: 1997-12-04
View all issues with NAD status.
Discussion:
Paragraph 1 in "Effects", says "Calls p->release()" where it clearly must be "Calls p.release()". (As it is, it seems to require using auto_ptr<>::operator-> to refer to X::release, assuming that exists.)
Proposed resolution:
Change 20.5.4.3 [meta.unary.prop] paragraph 1 Effects from "Calls p->release()" to "Calls p.release()".
Rationale:
Not a defect: the proposed change is already found in the standard. [Originally classified as a defect, later reclassified.]
Section: 21.3 [basic.string] Status: NAD Submitter: Beman Dawes Date: 1997-11-16
View other active issues in [basic.string].
View all other issues in [basic.string].
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Discussion:
In Morristown we changed the size_type and difference_type typedefs for all the other containers to implementation defined with a reference to 23.1 [container.requirements]. This should probably also have been done for strings.
Rationale:
Not a defect. [Originally classified as a defect, later reclassified.] basic_string, unlike the other standard library template containers, is severely constrained by its use of char_traits. Those types are dictated by the traits class, and are far from implementation defined.
Section: 27.4.3 [fpos] Status: NAD Submitter: Matt Austern Date: 1997-12-15
View all other issues in [fpos].
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Discussion:
Table 88, in I/O, is too strict; it's unimplementable on systems where a file position isn't just an offset. It also never says just what fpos<> is really supposed to be. [Here's my summary, which Jerry agrees is more or less accurate. "I think I now know what the class really is, at this point: it's a magic cookie that encapsulates an mbstate_t and a file position (possibly represented as an fpos_t), it has syntactic support for pointer-like arithmetic, and implementors are required to have real, not just syntactic, support for arithmetic." This isn't standardese, of course.]
Rationale:
Not a defect. The LWG believes that the Standard is already clear, and that the above summary is what the Standard in effect says.
Section: 22.2.1.5 [locale.codecvt.byname] Status: Dup Submitter: Matt Austern Date: 1998-01-14
View all other issues in [locale.codecvt.byname].
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Duplicate of: 19
Discussion:
Section 22.2.1.5.2 says that codecvt<>::do_in and do_out should return the value noconv if "no conversion was needed". However, I don't see anything anywhere that defines what it means for a conversion to be needed or not needed. I can think of several circumstances where one might plausibly think that a conversion is not "needed", but I don't know which one is intended here.
Rationale:
Section: 20.1.2 [allocator.requirements] Status: NAD Submitter: Angelika Langer Date: 1998-02-23
View other active issues in [allocator.requirements].
View all other issues in [allocator.requirements].
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Discussion:
I couldn't find a statement in the standard saying whether the allocator object held by a container is held as a copy of the constructor argument or whether a pointer of reference is maintained internal. There is an according statement for compare objects and how they are maintained by the associative containers, but I couldn't find anything regarding allocators.
Did I overlook it? Is it an open issue or known defect? Or is it deliberately left unspecified?
Rationale:
Not a defect. The LWG believes that the Standard is already clear. See 23.1 [container.requirements], paragraph 8.
Section: 22.2.1.5 [locale.codecvt.byname] Status: Dup Submitter: Brendan Kehoe Date: 1998-06-01
View all other issues in [locale.codecvt.byname].
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Duplicate of: 33
Discussion:
Rationale:
Section: 27.7.3 [ostringstream] Status: NAD Submitter: Matthias Mueller Date: 1998-05-27
View all issues with NAD status.
Discussion:
In a comp.lang.c++.moderated Matthias Mueller wrote:
"We are not sure how to interpret the CD2 (see 27.2 [iostream.forward], 27.7.3.1 [ostringstream.cons], 27.7.1.1 [stringbuf.cons]) with respect to the question as to what the correct initial positions of the write and read pointers of a stringstream should be."
"Is it the same to output two strings or to initialize the stringstream with the first and to output the second?"
[PJ Plauger, Bjarne Stroustrup, Randy Smithey, Sean Corfield, and Jerry Schwarz have all offered opinions; see reflector messages lib-6518, 6519, 6520, 6521, 6523, 6524.]
Rationale:
The LWG believes the Standard is correct as written. The behavior of stringstreams is consistent with fstreams, and there is a constructor which can be used to obtain the desired effect. This behavior is known to be different from strstreams.
Section: 27.6.1.2.3 [istream::extractors] Status: NAD Submitter: Matt Austern Date: 1998-07-01
View all other issues in [istream::extractors].
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Discussion:
27.6.1.2.3 has member functions for extraction of signed char and unsigned char, both singly and as strings. However, it doesn't say what it means to extract a char from a basic_streambuf<charT, Traits>.
basic_streambuf, after all, has no members to extract a char, so basic_istream must somehow convert from charT to signed char or unsigned char. The standard doesn't say how it is to perform that conversion.
Rationale:
The Standard is correct as written. There is no such extractor and this is the intent of the LWG.
Section: D.7.1.3 [depr.strstreambuf.virtuals] Status: NAD Submitter: Matt Austern Date: 1998-08-18
View all other issues in [depr.strstreambuf.virtuals].
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Discussion:
The standard says how this member function affects the current stream position. (gptr or pptr) However, it does not say how this member function affects the beginning and end of the get/put area.
This is an issue when seekoff is used to position the get pointer beyond the end of the current read area. (Which is legal. This is implicit in the definition of seekhigh in D.7.1, paragraph 4.)
Rationale:
The LWG agrees that seekoff() is underspecified, but does not wish to invest effort in this deprecated feature.
Section: 21.3.8.9 [string.io] Status: Dup Submitter: Steve Clamage Date: 1998-07-09
View all other issues in [string.io].
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Duplicate of: 25
Discussion:
In a comp.std.c++ posting Michel Michaud wrote: What should be output by:
string text("Hello");
cout << '[' << setw(10) << right << text << ']';
Shouldn't it be:
[ Hello]
Another person replied: Actually, according to the FDIS, the width of the field should be the minimum of width and the length of the string, so the output shouldn't have any padding. I think that this is a typo, however, and that what is wanted is the maximum of the two. (As written, setw is useless for strings. If that had been the intent, one wouldn't expect them to have mentioned using its value.)
It's worth pointing out that this is a recent correction anyway; IIRC, earlier versions of the draft forgot to mention formatting parameters whatsoever.
Rationale:
Section: 22.2.1.4 [locale.codecvt] Status: Dup Submitter: Nathan Myers Date: 1998-08-24
View all other issues in [locale.codecvt].
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Duplicate of: 24
Discussion:
In 22.2.1.4 [locale.codecvt] par 3, and in 22.2.1.4.2 [locale.codecvt.virtuals] par 8, a nonexistent member function "do_convert" is mentioned. This member was replaced with "do_in" and "do_out", the proper referents in the contexts above.
Rationale:
Section: 27.8.1 [fstreams] Status: NAD Submitter: Matt Austern Date: 1998-08-27
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Discussion:
Classes basic_ifstream, basic_ofstream, and basic_fstream all have a member function is_open. It should be a const member function, since it does nothing but call one of basic_filebuf's const member functions.
Rationale:
Not a defect. This is a deliberate feature; const streams would be meaningless.
Section: 26.5.2.3 [valarray.access] Status: Dup Submitter: Levente Farkas Date: 1998-09-09
View all other issues in [valarray.access].
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Duplicate of: 389
Discussion:
valarray:
T operator[] (size_t) const;
why not
const T& operator[] (size_t) const;
as in vector ???
One can't copy even from a const valarray eg:
memcpy(ptr, &v[0], v.size() * sizeof(double));
[I] find this bug in valarray is very difficult.
Rationale:
The LWG believes that the interface was deliberately designed that way. That is what valarray was designed to do; that's where the "value array" name comes from. LWG members further comment that "we don't want valarray to be a full STL container." 26.5.2.3 [valarray.access] specifies properties that indicate "an absence of aliasing" for non-constant arrays; this allows optimizations, including special hardware optimizations, that are not otherwise possible.
Section: 26.5.5 [template.slice.array], 26.5.7 [template.gslice.array], 26.5.8 [template.mask.array], 26.5.9 [template.indirect.array] Status: NAD Submitter: Nico Josuttis Date: 1998-09-29
View all other issues in [template.slice.array].
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Discussion:
Isn't the definition of copy constructor and assignment operators wrong? Instead of
slice_array(const slice_array&); slice_array& operator=(const slice_array&);
IMHO they have to be
slice_array(const slice_array<T>&); slice_array& operator=(const slice_array<T>&);
Same for gslice_array.
Rationale:
Not a defect. The Standard is correct as written.
Section: 23.1.4 [associative.reqmts] Status: NAD Submitter: Nico Josuttis Date: 1998-09-29
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Discussion:
Paragraph 5 specifies:
For set and multiset the value type is the same as the key type. For map and multimap it is equal to pair<const Key, T>.
Strictly speaking, this is not correct because for set and multiset the value type is the same as the constant key type.
Rationale:
Not a defect. The Standard is correct as written; it uses a different mechanism (const &) for set and multiset. See issue 103 for a related issue.
Section: 21.3.5 [string.access] Status: NAD Submitter: Nico Josuttis Date: 1998-09-29
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Discussion:
If I try
s.insert(0,1,' ');
I get an nasty ambiguity. It might be
s.insert((size_type)0,(size_type)1,(charT)' ');
which inserts 1 space character at position 0, or
s.insert((char*)0,(size_type)1,(charT)' ')
which inserts 1 space character at iterator/address 0 (bingo!), or
s.insert((char*)0, (InputIterator)1, (InputIterator)' ')
which normally inserts characters from iterator 1 to iterator ' '. But according to 23.1.1.9 (the "do the right thing" fix) it is equivalent to the second. However, it is still ambiguous, because of course I mean the first!
Rationale:
Not a defect. The LWG believes this is a "genetic misfortune" inherent in the design of string and thus not a defect in the Standard as such .
Section: 21 [strings] Status: NAD Submitter: Nico Josuttis Date: 1998-09-29
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Discussion:
The standard seems not to require that charT is equivalent to traits::char_type. So, what happens if charT is not equivalent to traits::char_type?
Rationale:
There is already wording in 21.1 [char.traits] paragraph 3 that requires them to be the same.
Section: 21.3.6.8 [string::swap] Status: Dup Submitter: Nico Josuttis Date: 1998-09-29
View all other issues in [string::swap].
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Duplicate of: 5
Discussion:
The following compare() description is obviously a bug:
int compare(size_type pos, size_type n1,
charT *s, size_type n2 = npos) const;
because without passing n2 it should compare up to the end of the string instead of comparing npos characters (which throws an exception)
Rationale:
Section: 21.3.6.4 [string::insert], 21.3.6.2 [string::append] Status: NAD Submitter: Nico Josuttis Date: 1998-09-29
View all other issues in [string::insert].
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Discussion:
Why does
template<class InputIterator>
basic_string& append(InputIterator first, InputIterator last);
return a string, while
template<class InputIterator>
void insert(iterator p, InputIterator first, InputIterator last);
returns nothing ?
Rationale:
The LWG believes this stylistic inconsistency is not sufficiently serious to constitute a defect.
Section: 21.3.6.4 [string::insert], 21.3.6.6 [string::replace] Status: Dup Submitter: Nico Josuttis Date: 1998-09-29
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Duplicate of: 83
Discussion:
All insert() and replace() members for strings with an iterator as first argument lack a throw specification. The throw specification should probably be: length_error if size exceeds maximum.
Rationale:
Considered a duplicate because it will be solved by the resolution of issue 83.
Section: 26.5 [numarray] Status: NAD Submitter: Nico Josuttis Date: 1998-09-29
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Discussion:
You can easily create subsets, but you can't easily combine them with other subsets. Unfortunately, you almost always needs an explicit type conversion to valarray. This is because the standard does not specify that valarray subsets provide the same operations as valarrays.
For example, to multiply two subsets and assign the result to a third subset, you can't write the following:
va[slice(0,4,3)] = va[slice(1,4,3)] * va[slice(2,4,3)];
Instead, you have to code as follows:
va[slice(0,4,3)] = static_cast<valarray<double> >(va[slice(1,4,3)]) *
static_cast<valarray<double> >(va[slice(2,4,3)]);
This is tedious and error-prone. Even worse, it costs performance because each cast creates a temporary objects, which could be avoided without the cast.
Proposed resolution:
Extend all valarray subset types so that they offer all valarray operations.
Rationale:
This is not a defect in the Standard; it is a request for an extension.
Section: 17.4.4 [conforming] Status: NAD Submitter: Matt Austern Date: 1998-01-22
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Discussion:
Is it a permitted extension for library implementors to add template parameters to standard library classes, provided that those extra parameters have defaults? For example, instead of defining template <class T, class Alloc = allocator<T> > class vector; defining it as template <class T, class Alloc = allocator<T>, int N = 1> class vector;
The standard may well already allow this (I can't think of any way that this extension could break a conforming program, considering that users are not permitted to forward-declare standard library components), but it ought to be explicitly permitted or forbidden.
comment from Steve Cleary via comp.std.c++:
I disagree [with the proposed resolution] for the following reason: consider user library code with template template parameters. For example, a user library object may be templated on the type of underlying sequence storage to use (deque/list/vector), since these classes all take the same number and type of template parameters; this would allow the user to determine the performance tradeoffs of the user library object. A similar example is a user library object templated on the type of underlying set storage (set/multiset) or map storage (map/multimap), which would allow users to change (within reason) the semantic meanings of operations on that object.
I think that additional template parameters should be forbidden in the Standard classes. Library writers don't lose any expressive power, and can still offer extensions because additional template parameters may be provided by a non-Standard implementation class:
template <class T, class Allocator = allocator<T>, int N = 1> class __vector { ... }; template <class T, class Allocator = allocator<T> > class vector: public __vector<T, Allocator> { ... };
Proposed resolution:
Add a new subclause [presumably 17.4.4.9] following 17.4.4.9 [res.on.exception.handling]:
17.4.4.9 Template Parameters
A specialization of a template class described in the C++ Standard Library behaves the same as if the implementation declares no additional template parameters.
Footnote: Additional template parameters with default values are thus permitted.
Add "template parameters" to the list of subclauses at the end of 17.4.4 [conforming] paragraph 1.
[Kona: The LWG agreed the standard needs clarification. After discussion with John Spicer, it seems added template parameters can be detected by a program using template-template parameters. A straw vote - "should implementors be allowed to add template parameters?" found no consensus ; 5 - yes, 7 - no.]
Rationale:
There is no ambiguity; the standard is clear as written. Library implementors are not permitted to add template parameters to standard library classes. This does not fall under the "as if" rule, so it would be permitted only if the standard gave explicit license for implementors to do this. This would require a change in the standard.
The LWG decided against making this change, because it would break user code involving template template parameters or specializations of standard library class templates.
Section: 17.4.4.4 [member.functions] Status: NAD Submitter: AFNOR Date: 1998-10-07
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Discussion:
In 17.3.4.4/2 vs 17.3.4.7/0 there is a hole; an implementation could add virtual members a base class and break user derived classes.
Example:
// implementation code:
struct _Base { // _Base is in the implementer namespace
virtual void foo ();
};
class vector : _Base // deriving from a class is allowed
{ ... };
// user code:
class vector_checking : public vector
{
void foo (); // don't want to override _Base::foo () as the
// user doesn't know about _Base::foo ()
};
Proposed resolution:
Clarify the wording to make the example illegal.
Rationale:
This is not a defect in the Standard. The example is already illegal. See 17.4.4.4 [member.functions] paragraph 2.
Section: 23 [containers] Status: NAD Submitter: AFNOR Date: 1998-10-07
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Discussion:
insert(iterator, const value_type&) is defined both on sequences and on set, with unrelated semantics: insert here (in sequences), and insert with hint (in associative containers). They should have different names (B.S. says: do not abuse overloading).
Rationale:
This is not a defect in the Standard. It is a genetic misfortune of the design, for better or for worse.
Section: 24.4.1.3.13 [reverse.iter.op==] Status: NAD Submitter: AFNOR Date: 1998-10-07
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Discussion:
The <, >, <=, >= comparison operator are wrong: they return the opposite of what they should.
Note: same problem in CD2, these were not even defined in CD1. SGI STL code is correct; this problem is known since the Morristown meeting but there it was too late
Rationale:
This is not a defect in the Standard. A careful reading shows the Standard is correct as written. A review of several implementations show that they implement exactly what the Standard says.
Section: 24.4.2 [insert.iterators], 24.5.4 [ostreambuf.iterator] Status: NAD Submitter: AFNOR Date: 1998-10-07
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Discussion:
Overspecified For an insert iterator it, the expression *it is required to return a reference to it. This is a simple possible implementation, but as the SGI STL documentation says, not the only one, and the user should not assume that this is the case.
Rationale:
The LWG believes this causes no harm and is not a defect in the standard. The only example anyone could come up with caused some incorrect code to work, rather than the other way around.
Section: 23.2.6 [vector], 23.2.1 [array] Status: NAD Submitter: AFNOR Date: 1998-10-07
View all other issues in [vector].
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Discussion:
Reserve can not free storage, unlike string::reserve
Rationale:
This is not a defect in the Standard. The LWG has considered this issue in the past and sees no need to change the Standard. Deque has no reserve() member function. For vector, shrink-to-fit can be expressed in a single line of code (where v is vector<T>):
vector<T>(v).swap(v); // shrink-to-fit v
Section: 23.1.4 [associative.reqmts] Status: Dup Submitter: AFNOR Date: 1998-10-07
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Duplicate of: 264
Discussion:
Table 69 of Containers say that a.insert(i,j) is linear if [i, j) is ordered. It seems impossible to implement, as it means that if [i, j) = [x], insert in an associative container is O(1)!
Proposed resolution:
N+log (size()) if [i,j) is sorted according to value_comp()
Rationale:
Subsumed by issue 264.
Section: 21.3.4 [string.capacity] Status: NAD Submitter: AFNOR Date: 1998-10-07
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Discussion:
It is not clear that undefined behavior applies when pos == size () for the non const version.
Proposed resolution:
Rewrite as: Otherwise, if pos > size () or pos == size () and the non-const version is used, then the behavior is undefined.
Rationale:
The Standard is correct. The proposed resolution already appears in the Standard.
Section: 27.8 [file.streams] Status: Dup Submitter: AFNOR Date: 1998-10-07
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Duplicate of: 454
Discussion:
fstream ctors take a const char* instead of string.
fstream ctors can't take wchar_t
An extension to add a const wchar_t* to fstream would make the implementation non conforming.
Rationale:
This is not a defect in the Standard. It might be an interesting extension for the next Standard.
Section: 26.5.2 [template.valarray] Status: NAD Submitter: AFNOR Date: 1998-10-07
View all other issues in [template.valarray].
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Discussion:
The order of the arguments is (elem, size) instead of the normal (size, elem) in the rest of the library. Since elem often has an integral or floating point type, both types are convertible to each other and reversing them leads to a well formed program.
Proposed resolution:
Inverting the arguments could silently break programs. Introduce the two signatures (const T&, size_t) and (size_t, const T&), but make the one we do not want private so errors result in a diagnosed access violation. This technique can also be applied to STL containers.
Rationale:
The LWG believes that while the order of arguments is unfortunate, it does not constitute a defect in the standard. The LWG believes that the proposed solution will not work for valarray<size_t> and perhaps other cases.
Section: 24.5.3.5 [istreambuf.iterator::equal] Status: NAD Future Submitter: Nathan Myers Date: 1998-10-15
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Discussion:
The member istreambuf_iterator<>::equal is specified to be unnecessarily inefficient. While this does not affect the efficiency of conforming implementations of iostreams, because they can "reach into" the iterators and bypass this function, it does affect users who use istreambuf_iterators.
The inefficiency results from a too-scrupulous definition, which requires a "true" result if neither iterator is at eof. In practice these iterators can only usefully be compared with the "eof" value, so the extra test implied provides no benefit, but slows down users' code.
The solution is to weaken the requirement on the function to return true only if both iterators are at eof.
Proposed resolution:
Replace 24.5.3.5 [istreambuf.iterator::equal], paragraph 1,
-1- Returns: true if and only if both iterators are at end-of-stream, or neither is at end-of-stream, regardless of what streambuf object they use.
with
-1- Returns: true if and only if both iterators are at end-of-stream, regardless of what streambuf object they use.
Rationale:
It is not clear that this is a genuine defect. Additionally, the LWG was reluctant to make a change that would result in operator== not being a equivalence relation. One consequence of this change is that an algorithm that's passed the range [i, i) would no longer treat it as an empty range.
Section: 27.6.1.1 [istream], 27.6.1.3 [istream.unformatted] Status: NAD Submitter: Steve Clamage Date: 1998-10-13
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Discussion:
In 27.6.1.1, class basic_istream has a member function sync, described in 27.6.1.3, paragraph 36.
Following the chain of definitions, I find that the various sync functions have defined semantics for output streams, but no semantics for input streams. On the other hand, basic_ostream has no sync function.
The sync function should at minimum be added to basic_ostream, for internal consistency.
A larger question is whether sync should have assigned semantics for input streams.
Classic iostreams said streambuf::sync flushes pending output and attempts to return unread input characters to the source. It is a protected member function. The filebuf version (which is public) has that behavior (it backs up the read pointer). Class strstreambuf does not override streambuf::sync, and so sync can't be called on a strstream.
If we can add corresponding semantics to the various sync functions, we should. If not, we should remove sync from basic_istream.
Rationale:
A sync function is not needed in basic_ostream because the flush function provides the desired functionality.
As for the other points, the LWG finds the standard correct as written.
Section: 23.3.5 [template.bitset] Status: Dup Submitter: Judy Ward Date: 1998-11-06
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Duplicate of: 778
Discussion:
The following code does not compile with the EDG compiler:
#include <bitset>
using namespace std;
bitset<32> b("111111111");
If you cast the ctor argument to a string, i.e.:
bitset<32> b(string("111111111"));
then it will compile. The reason is that bitset has the following templatized constructor:
template <class charT, class traits, class Allocator> explicit bitset (const basic_string<charT, traits, Allocator>& str, ...);
According to the compiler vendor, Steve Adamcyk at EDG, the user cannot pass this template constructor a const char* and expect a conversion to basic_string. The reason is "When you have a template constructor, it can get used in contexts where type deduction can be done. Type deduction basically comes up with exact matches, not ones involving conversions."
I don't think the intention when this constructor became templatized was for construction from a const char* to no longer work.
Proposed resolution:
Add to 23.3.5 [template.bitset] a bitset constructor declaration
explicit bitset(const char*);
and in Section 23.3.5.1 [bitset.cons] add:
explicit bitset(const char* str);Effects:
Calls bitset((string) str, 0, string::npos);
Rationale:
Although the problem is real, the standard is designed that way so it is not a defect. Education is the immediate workaround. A future standard may wish to consider the Proposed Resolution as an extension.
Section: 22.1.1.1.1 [locale.category] Status: NAD Submitter: Judy Ward Date: 1998-12-15
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Discussion:
Section 22.1.1.1.1 has the following listed in Table 51: ctype<char> , ctype<wchar_t>.
Also Section 22.2.1.1 [locale.ctype] says:
The instantiations required in Table 51 (22.1.1.1.1) namely ctype<char> and ctype<wchar_t> , implement character classing appropriate to the implementation's native character set.
However, Section 22.2.1.3 [facet.ctype.special] only has a detailed description of the ctype<char> specialization, not the ctype<wchar_t> specialization.
Proposed resolution:
Add the ctype<wchar_t> detailed class description to Section 22.2.1.3 [facet.ctype.special].
Rationale:
Specialization for wchar_t is not needed since the default is acceptable.
Section: 23.2.4.4 [list.ops] Status: NAD Submitter: Howard Hinnant Date: 1999-03-06
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Discussion:
What happens if a splice operation causes the size() of a list to grow beyond max_size()?
Rationale:
Size() cannot grow beyond max_size().
Section: 27.6.1.5.1 [iostream.cons] Status: NAD Submitter: Howard Hinnant Date: 1999-03-06
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Discussion:
-1- Effects Constructs an object of class basic_iostream, assigning initial values to the base classes by calling basic_istream<charT,traits>(sb) (lib.istream) and basic_ostream<charT,traits>(sb) (lib.ostream)
The called for basic_istream and basic_ostream constructors call init(sb). This means that the basic_iostream's virtual base class is initialized twice.
Proposed resolution:
Change 27.6.1.5.1, paragraph 1 to:
-1- Effects Constructs an object of class basic_iostream, assigning initial values to the base classes by calling basic_istream<charT,traits>(sb) (lib.istream).
Rationale:
The LWG agreed that the init() function is called twice, but said that this is harmless and so not a defect in the standard.
Section: 22.2.1.4 [locale.codecvt] Status: NAD Future Submitter: Angelika Langer Date: 1999-03-18
View all other issues in [locale.codecvt].
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Discussion:
Section 22.2.1.4 [locale.codecvt] specifies that ctype_byname<char> must be a specialization of the ctype_byname template.
It is common practice in the standard that specializations of class templates are only mentioned where the interface of the specialization deviates from the interface of the template that it is a specialization of. Otherwise, the fact whether or not a required instantiation is an actual instantiation or a specialization is left open as an implementation detail.
Clause 22.2.1.4 deviates from that practice and for that reason is misleading. The fact, that ctype_byname<char> is specified as a specialization suggests that there must be something "special" about it, but it has the exact same interface as the ctype_byname template. Clause 22.2.1.4 does not have any explanatory value, is at best redundant, at worst misleading - unless I am missing anything.
Naturally, an implementation will most likely implement ctype_byname<char> as a specialization, because the base class ctype<char> is a specialization with an interface different from the ctype template, but that's an implementation detail and need not be mentioned in the standard.
Rationale:
The standard as written is mildly misleading, but the correct fix is to deal with the underlying problem in the ctype_byname base class, not in the specialization. See issue 228.
Section: 23.3.1 [map] Status: NAD Editorial Submitter: Mark Mitchell Date: 1999-04-14
View all other issues in [map].
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Discussion:
23.1 [container.requirements]
expression return type pre/post-condition
------------- ----------- -------------------
X::value_type T T is assignable
23.3.1 [map]
A map satisfies all the requirements of a container.
For a map<Key, T> ... the value_type is pair<const Key, T>.
There's a contradiction here. In particular, `pair<const Key, T>' is not assignable; the `const Key' cannot be assigned to. So, map<Key, T>::value_type does not satisfy the assignable requirement imposed by a container.
[See issue 103 for the slightly related issue of modification of set keys.]
Rationale:
The LWG believes that the standard is inconsistent, but that this is a design problem rather than a strict defect. May wish to reconsider for the next standard.
Section: D.5 [depr.c.headers] Status: NAD Submitter: Christophe de Dinechin Date: 1999-05-04
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Discussion:
[depr.c.headers] paragraph 2 reads:
Each C header, whose name has the form name.h, behaves as if each name placed in the Standard library namespace by the corresponding cname header is also placed within the namespace scope of the namespace std and is followed by an explicit using-declaration (_namespace.udecl_)
I think it should mention the global name space somewhere... Currently, it indicates that name placed in std is also placed in std...
I don't know what is the correct wording. For instance, if struct tm is defined in time.h, ctime declares std::tm. However, the current wording seems ambiguous regarding which of the following would occur for use of both ctime and time.h:
// version 1:
namespace std {
struct tm { ... };
}
using std::tm;
// version 2:
struct tm { ... };
namespace std {
using ::tm;
}
// version 3:
struct tm { ... };
namespace std {
struct tm { ... };
}
I think version 1 is intended.
[Kona: The LWG agreed that the wording is not clear. It also agreed that version 1 is intended, version 2 is not equivalent to version 1, and version 3 is clearly not intended. The example below was constructed by Nathan Myers to illustrate why version 2 is not equivalent to version 1.
Although not equivalent, the LWG is unsure if (2) is enough of a problem to be prohibited. Points discussed in favor of allowing (2):
- It may be a convenience to implementors.
- The only cases that fail are structs, of which the C library contains only a few.
]
Example:
#include <time.h>
#include <utility>
int main() {
std::tm * t;
make_pair( t, t ); // okay with version 1 due to Koenig lookup
// fails with version 2; make_pair not found
return 0;
}
Proposed resolution:
Replace D.5 [depr.c.headers] paragraph 2 with:
Each C header, whose name has the form name.h, behaves as if each name placed in the Standard library namespace by the corresponding cname header is also placed within the namespace scope of the namespace std by name.h and is followed by an explicit using-declaration (_namespace.udecl_) in global scope.
Rationale:
The current wording in the standard is the result of a difficult compromise that averted delay of the standard. Based on discussions in Tokyo it is clear that there is no still no consensus on stricter wording, so the issue has been closed. It is suggested that users not write code that depends on Koenig lookup of C library functions.
Section: 27.4.4.1 [basic.ios.cons] Status: NAD Submitter: Angelika Langer Date: 1999-05-12
View all other issues in [basic.ios.cons].
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Discussion:
There is no initial value for the adjustfield defined, although many people believe that the default adjustment were right. This is a common misunderstanding. The standard only defines that, if no adjustment is specified, all the predefined inserters must add fill characters before the actual value, which is "as if" the right flag were set. The flag itself need not be set.
When you implement a user-defined inserter you cannot rely on right being the default setting for the adjustfield. Instead, you must be prepared to find none of the flags set and must keep in mind that in this case you should make your inserter behave "as if" the right flag were set. This is surprising to many people and complicates matters more than necessary.
Unless there is a good reason why the adjustfield should not be initialized I would suggest to give it the default value that everybody expects anyway.
Rationale:
This is not a defect. It is deliberate that the default is no bits set. Consider Arabic or Hebrew, for example. See 22.2.2.2.2 [facet.num.put.virtuals] paragraph 19, Table 61 - Fill padding.
Section: 23.1.3 [sequence.reqmts] Status: NAD Future Submitter: Andrew Koenig Date: 1999-06-28
View all other issues in [sequence.reqmts].
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Discussion:
Suppose that c and c1 are sequential containers and i is an iterator that refers to an element of c. Then I can insert a copy of c1's elements into c ahead of element i by executing
c.insert(i, c1.begin(), c1.end());
If c is a vector, it is fairly easy for me to find out where the newly inserted elements are, even though i is now invalid:
size_t i_loc = i - c.begin(); c.insert(i, c1.begin(), c1.end());
and now the first inserted element is at c.begin()+i_loc and one
past the last is at c.begin()+i_loc+c1.size().
But what if c is a list? I can still find the location of one past the
last inserted element, because i is still valid. To find the location
of the first inserted element, though, I must execute something like
for (size_t n = c1.size(); n; --n) --i;
because i is now no longer a random-access iterator.
Alternatively, I might write something like
bool first = i == c.begin(); list<T>::iterator j = i; if (!first) --j; c.insert(i, c1.begin(), c1.end()); if (first) j = c.begin(); else ++j;
which, although wretched, requires less overhead.
But I think the right solution is to change the definition of insert
so that instead of returning void, it returns an iterator that refers
to the first element inserted, if any, and otherwise is a copy of its
first argument.
Rationale:
The LWG believes this was an intentional design decision and so is not a defect. It may be worth revisiting for the next standard.
Section: 27.4.2.5 [ios.base.storage] Status: Dup Submitter: Dietmar Kühl Date: 1999-07-20
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Duplicate of: 41
Discussion:
According to paragraphs 2 and 4 of 27.4.2.5 [ios.base.storage], the functions iword() and pword() "set the badbit (which might throw an exception)" on failure. ... but what does it mean for ios_base to set the badbit? The state facilities of the IOStream library are defined in basic_ios, a derived class! It would be possible to attempt a down cast but then it would be necessary to know the character type used...
Rationale:
Section: 27.6.1.2.3 [istream::extractors] Status: Dup Submitter: Dietmar Kühl Date: 1999-07-20
View all other issues in [istream::extractors].
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Duplicate of: 60
Discussion:
It appears to be somewhat nonsensical to consider the functions defined in the paragraphs 1 to 5 to be "Formatted input function" but since these functions are defined in a section labeled "Formatted input functions" it is unclear to me whether these operators are considered formatted input functions which have to conform to the "common requirements" from 27.6.1.2.1 [istream.formatted.reqmts]: If this is the case, all manipulators, not just ws, would skip whitespace unless noskipws is set (... but setting noskipws using the manipulator syntax would also skip whitespace :-)
See also issue 166 for the same problem in formatted output
Rationale:
Section: 27.6.1.3 [istream.unformatted] Status: Dup Submitter: Dietmar Kühl Date: 1999-07-20
View all other issues in [istream.unformatted].
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Duplicate of: 60
Discussion:
It is not clear which functions are to be considered unformatted input functions. As written, it seems that all functions in 27.6.1.3 [istream.unformatted] are unformatted input functions. However, it does not really make much sense to construct a sentry object for gcount(), sync(), ... Also it is unclear what happens to the gcount() if eg. gcount(), putback(), unget(), or sync() is called: These functions don't extract characters, some of them even "unextract" a character. Should this still be reflected in gcount()? Of course, it could be read as if after a call to gcount() gcount() return 0 (the last unformatted input function, gcount(), didn't extract any character) and after a call to putback() gcount() returns -1 (the last unformatted input function putback() did "extract" back into the stream). Correspondingly for unget(). Is this what is intended? If so, this should be clarified. Otherwise, a corresponding clarification should be used.
Rationale:
Section: 27.6.2.6.3 [ostream.inserters] Status: Dup Submitter: Dietmar Kühl Date: 1999-07-20
View all issues with Dup status.
Duplicate of: 60
Discussion:
From 27.6.2.6.1 [ostream.formatted.reqmts] it appears that all the functions defined in 27.6.2.6.3 [ostream.inserters] have to construct a sentry object. Is this really intended?
This is basically the same problem as issue 162 but for output instead of input.
Rationale:
Section: 26.3.6 [complex.ops] Status: NAD Submitter: Judy Ward Date: 1999-07-02
View all other issues in [complex.ops].
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Discussion:
A user who tries to explicitly instantiate a complex non-member operator will get compilation errors. Below is a simplified example of the reason why. The problem is that iterator_traits cannot be instantiated on a non-pointer type like float, yet when the compiler is trying to decide which operator+ needs to be instantiated it must instantiate the declaration to figure out the first argument type of a reverse_iterator operator.
namespace std {
template <class Iterator>
struct iterator_traits
{
typedef typename Iterator::value_type value_type;
};
template <class T> class reverse_iterator;
// reverse_iterator operator+
template <class T>
reverse_iterator<T> operator+
(typename iterator_traits<T>::difference_type, const reverse_iterator<T>&);
template <class T> struct complex {};
// complex operator +
template <class T>
complex<T> operator+ (const T& lhs, const complex<T>& rhs)
{ return complex<T>();}
}
// request for explicit instantiation
template std::complex<float> std::operator+<float>(const float&,
const std::complex<float>&);
See also c++-stdlib reflector messages: lib-6814, 6815, 6816.
Rationale:
Implementors can make minor changes and the example will work. Users are not affected in any case.
According to John Spicer, It is possible to explicitly instantiate these operators using different syntax: change "std::operator+<float>" to "std::operator+".
The proposed resolution of issue 120 is that users will not be able to explicitly instantiate standard library templates. If that resolution is accepted then library implementors will be the only ones that will be affected by this problem, and they must use the indicated syntax.
Section: 27.3.1 [narrow.stream.objects] Status: NAD Submitter: Judy Ward Date: 1999-07-02
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Discussion:
Section 27.3.1 says "After the object cerr is initialized, cerr.flags() & unitbuf is nonzero. Its state is otherwise the same as required for ios_base::init (lib.basic.ios.cons). It doesn't say anything about the the state of clog. So this means that calling cerr.tie() and clog.tie() should return 0 (see Table 89 for ios_base::init effects).
Neither of the popular standard library implementations that I tried does this, they both tie cerr and clog to &cout. I would think that would be what users expect.
Rationale:
The standard is clear as written.
27.3.1/5 says that "After the object cerr is initialized, cerr.flags() & unitbuf is nonzero. Its state is otherwise the same as required for ios_base::init (27.4.4.1)." Table 89 in 27.4.4.1, which gives the postconditions of basic_ios::init(), says that tie() is 0. (Other issues correct ios_base::init to basic_ios::init().)
Section: 26.5.2.6 [valarray.cassign] Status: NAD Submitter: Gabriel Dos Reis Date: 1999-08-15
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Discussion:
26.5.2.6 defines augmented assignment operators valarray<T>::op=(const T&), but fails to provide corresponding versions for the helper classes. Thus making the following illegal:
#include <valarray>
int main()
{
std::valarray<double> v(3.14, 1999);
v[99] *= 2.0; // Ok
std::slice s(0, 50, 2);
v[s] *= 2.0; // ERROR
}
I can't understand the intent of that omission. It makes the valarray library less intuitive and less useful.
Rationale:
Although perhaps an unfortunate design decision, the omission is not a defect in the current standard. A future standard may wish to add the missing operators.
Section: 25.3.3 [alg.binary.search] Status: NAD Submitter: Nico Josuttis Date: 1999-10-10
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Discussion:
The complexity of binary_search() is stated as "At most
log(last-first) + 2 comparisons", which seems to say that the
algorithm has logarithmic complexity. However, this algorithms is
defined for forward iterators. And for forward iterators, the need to
step element-by-element results into linear complexity. But such a
statement is missing in the standard. The same applies to
lower_bound(), upper_bound(), and equal_range().
However, strictly speaking the standard contains no bug here. So this
might considered to be a clarification or improvement.
Rationale:
The complexity is expressed in terms of comparisons, and that complexity can be met even if the number of iterators accessed is linear. Paragraph 1 already says exactly what happens to iterators.
Section: 23.1.4 [associative.reqmts] Status: NAD Submitter: Ed Brey Date: 1999-06-06
View all other issues in [associative.reqmts].
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Duplicate of: 233
Discussion:
As defined in 23.1.2, paragraph 7 (table 69), a.insert(p,t) suffers from several problems:
| expression | return type | pre/post-condition | complexity |
| a.insert(p,t) | iterator | inserts t if and only if there is no element with key equivalent to the key of t in containers with unique keys; always inserts t in containers with equivalent keys. always returns the iterator pointing to the element with key equivalent to the key of t . iterator p is a hint pointing to where the insert should start to search. | logarithmic in general, but amortized constant if t is inserted right after p . |
1. For a container with unique keys, only logarithmic complexity is guaranteed if no element is inserted, even though constant complexity is always possible if p points to an element equivalent to t.
2. For a container with equivalent keys, the amortized constant complexity guarantee is only useful if no key equivalent to t exists in the container. Otherwise, the insertion could occur in one of multiple locations, at least one of which would not be right after p.
3. By guaranteeing amortized constant complexity only when t is inserted after p, it is impossible to guarantee constant complexity if t is inserted at the beginning of the container. Such a problem would not exist if amortized constant complexity was guaranteed if t is inserted before p, since there is always some p immediately before which an insert can take place.
4. For a container with equivalent keys, p does not allow specification of where to insert the element, but rather only acts as a hint for improving performance. This negates the added functionality that p would provide if it specified where within a sequence of equivalent keys the insertion should occur. Specifying the insert location provides more control to the user, while providing no disadvantage to the container implementation.
Proposed resolution:
In 23.1.4 [associative.reqmts] paragraph 7, replace the row in table 69 for a.insert(p,t) with the following two rows:
| expression | return type | pre/post-condition | complexity |
| a_uniq.insert(p,t) | iterator | inserts t if and only if there is no element with key equivalent to the key of t. returns the iterator pointing to the element with key equivalent to the key of t. | logarithmic in general, but amortized constant if t is inserted right before p or p points to an element with key equivalent to t. |
| a_eq.insert(p,t) | iterator | inserts t and returns the iterator pointing to the newly inserted element. t is inserted right before p if doing so preserves the container ordering. | logarithmic in general, but amortized constant if t is inserted right before p. |
Rationale:
Too big a change. Furthermore, implementors report checking both before p and after p, and don't want to change this behavior.
Section: 27.4.4 [ios] Status: NAD Submitter: Steve Clamage Date: 1999-09-07
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Discussion:
In classic iostreams, base class ios had an rdbuf function that returned a pointer to the associated streambuf. Each derived class had its own rdbuf function that returned a pointer of a type reflecting the actual type derived from streambuf. Because in ARM C++, virtual function overrides had to have the same return type, rdbuf could not be virtual.
In standard iostreams, we retain the non-virtual rdbuf function design, and in addition have an overloaded rdbuf function that sets the buffer pointer. There is no need for the second function to be virtual nor to be implemented in derived classes.
Minor question: Was there a specific reason not to make the original rdbuf function virtual?
Major problem: Friendly compilers warn about functions in derived classes that hide base-class overloads. Any standard implementation of iostreams will result in such a warning on each of the iostream classes, because of the ill-considered decision to overload rdbuf only in a base class.
In addition, users of the second rdbuf function must use explicit qualification or a cast to call it from derived classes. An explicit qualification or cast to basic_ios would prevent access to any later overriding version if there was one.
What I'd like to do in an implementation is add a using- declaration for the second rdbuf function in each derived class. It would eliminate warnings about hiding functions, and would enable access without using explicit qualification. Such a change I don't think would change the behavior of any valid program, but would allow invalid programs to compile:
filebuf mybuf; fstream f; f.rdbuf(mybuf); // should be an error, no visible rdbuf
I'd like to suggest this problem as a defect, with the proposed resolution to require the equivalent of a using-declaration for the rdbuf function that is not replaced in a later derived class. We could discuss whether replacing the function should be allowed.
Rationale:
For historical reasons, the standard is correct as written. There is a subtle difference between the base class rdbuf() and derived class rdbuf(). The derived class rdbuf() always returns the original streambuf, whereas the base class rdbuf() will return the "current streambuf" if that has been changed by the variant you mention.
Permission is not required to add such an extension. See 17.4.4.4 [member.functions].
Section: 18.5.1.3 [new.delete.placement] Status: Dup Submitter: Herb Sutter Date: 1998-12-15
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Duplicate of: 114
Discussion:
The example in 18.5.1.3 [new.delete.placement] paragraph 4 reads:
[Example: This can be useful for constructing an object at a known address:
char place[sizeof(Something)];
Something* p = new (place) Something();
end example]
This example has potential alignment problems.
Rationale:
Section: 20.1.2 [allocator.requirements], 23.1 [container.requirements] Status: NAD Submitter: Andy Sawyer Date: 1999-10-21
View other active issues in [allocator.requirements].
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Discussion:
Must the value returned by max_size() be unchanged from call to call?
Must the value returned from max_size() be meaningful?
Possible meanings identified in lib-6827:
1) The largest container the implementation can support given "best
case" conditions - i.e. assume the run-time platform is "configured to
the max", and no overhead from the program itself. This may possibly
be determined at the point the library is written, but certainly no
later than compile time.
2) The largest container the program could create, given "best case"
conditions - i.e. same platform assumptions as (1), but take into
account any overhead for executing the program itself. (or, roughly
"storage=storage-sizeof(program)"). This does NOT include any resource
allocated by the program. This may (or may not) be determinable at
compile time.
3) The largest container the current execution of the program could
create, given knowledge of the actual run-time platform, but again,
not taking into account any currently allocated resource. This is
probably best determined at program start-up.
4) The largest container the current execution program could create at
the point max_size() is called (or more correctly at the point
max_size() returns :-), given it's current environment (i.e. taking
into account the actual currently available resources). This,
obviously, has to be determined dynamically each time max_size() is
called.
Proposed resolution:
Rationale:
max_size() isn't useful for very many things, and the existing wording is sufficiently clear for the few cases that max_size() can be used for. None of the attempts to change the existing wording were an improvement.
It is clear to the LWG that the value returned by max_size() can't change from call to call.
Section: 27.6.1.1.3 [istream::sentry] Status: NAD Submitter: Matt McClure and Dietmar Kühl Date: 2000-01-01
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Discussion:
27.6.1.1.2 Paragraph 4 states:
To decide if the character c is a whitespace character, the constructor performs ''as if'' it executes the following code fragment:
const ctype<charT>& ctype = use_facet<ctype<charT> >(is.getloc()); if (ctype.is(ctype.space,c)!=0) // c is a whitespace character.
But Table 51 in 22.1.1.1.1 only requires an implementation to provide specializations for ctype<char> and ctype<wchar_t>. If sentry's constructor is implemented using ctype, it will be uninstantiable for a user-defined character type charT, unless the implementation has provided non-working (since it would be impossible to define a correct ctype<charT> specialization for an arbitrary charT) definitions of ctype's virtual member functions.
It seems the intent the standard is that sentry should behave, in every respect, not just during execution, as if it were implemented using ctype, with the burden of providing a ctype specialization falling on the user. But as it is written, nothing requires the translation of sentry's constructor to behave as if it used the above code, and it would seem therefore, that sentry's constructor should be instantiable for all character types.
Note: If I have misinterpreted the intent of the standard with respect to sentry's constructor's instantiability, then a note should be added to the following effect:
An implementation is forbidden from using the above code if it renders the constructor uninstantiable for an otherwise valid character type.
In any event, some clarification is needed.
Rationale:
It is possible but not easy to instantiate on types other than char or wchar_t; many things have to be done first. That is by intention and is not a defect.
Section: 24.3.4 [iterator.operations] Status: NAD Submitter: Rintala Matti Date: 2000-01-28
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Discussion:
Section 24.3.4 describes the function distance(first, last) (where first and last are iterators) which calculates "the number of increments or decrements needed to get from 'first' to 'last'".
The function should work for forward, bidirectional and random access iterators, and there is a requirement 24.3.4.5 which states that "'last' must be reachable from 'first'".
With random access iterators the function is easy to implement as "last - first".
With forward iterators it's clear that 'first' must point to a place before 'last', because otherwise 'last' would not be reachable from 'first'.
But what about bidirectional iterators? There 'last' is reachable from 'first' with the -- operator even if 'last' points to an earlier position than 'first'. However, I cannot see how the distance() function could be implemented if the implementation does not know which of the iterators points to an earlier position (you cannot use ++ or -- on either iterator if you don't know which direction is the "safe way to travel").
The paragraph 24.3.4.1 states that "for ... bidirectional iterators they use ++ to provide linear time implementations". However, the ++ operator is not mentioned in the reachability requirement. Furthermore 24.3.4.4 explicitly mentions that distance() returns the number of increments _or decrements_, suggesting that it could return a negative number also for bidirectional iterators when 'last' points to a position before 'first'.
Is a further requirement is needed to state that for forward and bidirectional iterators "'last' must be reachable from 'first' using the ++ operator". Maybe this requirement might also apply to random access iterators so that distance() would work the same way for every iterator category?
Rationale:
"Reachable" is defined in the standard in 24.1 [iterator.requirements] paragraph 6. The definition is only in terms of operator++(). The LWG sees no defect in the standard.
Section: 18.2.1.2 [numeric.limits.members] Status: NAD Submitter: Steve Cleary Date: 2000-01-28
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Discussion:
In several places in 18.2.1.2 [numeric.limits.members], a member is described as "Meaningful for all floating point types." However, no clear method of determining a floating point type is provided.
In 18.2.1.5 [numeric.special], paragraph 1 states ". . . (for example, epsilon() is only meaningful if is_integer is false). . ." which suggests that a type is a floating point type if is_specialized is true and is_integer is false; however, this is unclear.
When clarifying this, please keep in mind this need of users: what exactly is the definition of floating point? Would a fixed point or rational representation be considered one? I guess my statement here is that there could also be types that are neither integer or (strictly) floating point.
Rationale:
It is up to the implementor of a user define type to decide if it is a floating point type.
Section: 22.2.1.3.2 [facet.ctype.char.members] Status: Dup Submitter: Robert Klarer Date: 1999-11-02
View all other issues in [facet.ctype.char.members].
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Duplicate of: 153
Discussion:
The widen and narrow member functions are described in 22.2.1.3.2, paragraphs 9-11. In each case we have two overloaded signatures followed by a Returns clause. The Returns clause only describes one of the overloads.
Proposed resolution:
Change the returns clause in 22.2.1.3.2 [facet.ctype.char.members] paragraph 10 from:
Returns: do_widen(low, high, to).
to:
Returns: do_widen(c) or do_widen(low, high, to), respectively.
Change the returns clause in 22.2.1.3.2 [facet.ctype.char.members] paragraph 11 from:
Returns: do_narrow(low, high, to).
to:
Returns: do_narrow(c) or do_narrow(low, high, to), respectively.
Rationale:
Subsumed by issue 153, which addresses the same paragraphs.
Section: 26.7 [c.math] Status: NAD Submitter: Nico Josuttis Date: 2000-02-26
View all other issues in [c.math].
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Discussion:
Due to the additional overloaded versions of numeric functions for float and long double according to Section 26.5, calls such as int x; std::pow (x, 4) are ambiguous now in a standard conforming implementation. Current implementations solve this problem very different (overload for all types, don't overload for float and long double, use preprocessor, follow the standard and get ambiguities).
This behavior should be standardized or at least identified as implementation defined.
Rationale:
These math issues are an understood and accepted consequence of the design. They have been discussed several times in the past. Users must write casts or write floating point expressions as arguments.
Section: 23.1.4 [associative.reqmts] Status: NAD Submitter: Judy Ward Date: 2000-02-29
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Discussion:
A user noticed that this doesn't compile with the Rogue Wave library because the rb_tree class declares a key_allocator, and allocator<const int> is not legal, I think:
map < const int, ... > // legal?
which made me wonder whether it is legal for a map's key_type to be const. In email from Matt Austern he said:
I'm not sure whether it's legal to declare a map with a const key type. I hadn't thought about that question until a couple weeks ago. My intuitive feeling is that it ought not to be allowed, and that the standard ought to say so. It does turn out to work in SGI's library, though, and someone in the compiler group even used it. Perhaps this deserves to be written up as an issue too.
Rationale:
The "key is assignable" requirement from table 69 in 23.1.4 [associative.reqmts] already implies the key cannot be const.
Section: 27.6.3 [std.manip] Status: Dup Submitter: Hyman Rosen Date: 2000-02-29
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Duplicate of: 193
Discussion:
27.6.3 [std.manip] paragraph 5 says:
smanip setbase(int base);Returns: An object s of unspecified type such that if out is an (instance of) basic_ostream then the expression out<<s behaves as if f(s) were called, in is an (instance of) basic_istream then the expression in>>s behaves as if f(s) were called. Where f can be defined as:
ios_base& f(ios_base& str, int base) { // set basefield str.setf(n == 8 ? ios_base::oct : n == 10 ? ios_base::dec : n == 16 ? ios_base::hex : ios_base::fmtflags(0), ios_base::basefield); return str; }
There are two problems here. First, f takes two parameters, so the description needs to say that out<<s and in>>s behave as if f(s,base) had been called. Second, f is has a parameter named base, but is written as if the parameter was named n.
Actually, there's a third problem. The paragraph has grammatical errors. There needs to be an "and" after the first comma, and the "Where f" sentence fragment needs to be merged into its preceding sentence. You may also want to format the function a little better. The formatting above is more-or-less what the Standard contains.
Rationale:
The resolution of this defect is subsumed by the proposed resolution for issue 193.
[Tokyo: The LWG agrees that this is a defect and notes that it occurs additional places in the section, all requiring fixes.]
Section: 25.3 [alg.sorting] Status: NAD Submitter: Pablo Halpern Date: 2000-03-06
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Discussion:
Many of the algorithms take an argument, pred, of template parameter type BinaryPredicate or an argument comp of template parameter type Compare. These algorithms usually have an overloaded version that does not take the predicate argument. In these cases pred is usually replaced by the use of operator== and comp is replaced by the use of operator<.
This use of hard-coded operators is inconsistent with other parts of the library, particularly the containers library, where equality is established using equal_to<> and ordering is established using less<>. Worse, the use of operator<, would cause the following innocent-looking code to have undefined behavior:
vector<string*> vec; sort(vec.begin(), vec.end());
The use of operator< is not defined for pointers to unrelated objects. If std::sort used less<> to compare elements, then the above code would be well-defined, since less<> is explicitly specialized to produce a total ordering of pointers.
Rationale:
This use of operator== and operator< was a very deliberate, conscious, and explicitly made design decision; these operators are often more efficient. The predicate forms are available for users who don't want to rely on operator== and operator<.
Section: 25.1.5 [alg.find] Status: NAD Future Submitter: Pablo Halpern Date: 2000-03-06
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Discussion:
The find function always searches for a value using operator== to compare the value argument to each element in the input iterator range. This is inconsistent with other find-related functions such as find_end and find_first_of, which allow the caller to specify a binary predicate object to be used for determining equality. The fact that this can be accomplished using a combination of find_if and bind_1st or bind_2nd does not negate the desirability of a consistent, simple, alternative interface to find.
Proposed resolution:
In section 25.1.5 [alg.find], add a second prototype for find (between the existing prototype and the prototype for find_if), as follows:
template<class InputIterator, class T, class BinaryPredicate> InputIterator find(InputIterator first, InputIterator last, const T& value, BinaryPredicate bin_pred);Change the description of the return from:
Returns: The first iterator i in the range [first, last) for which the following corresponding conditions hold: *i == value, pred(*i) != false. Returns last if no such iterator is found.
to:
Returns: The first iterator i in the range [first, last) for which the following corresponding condition holds: *i == value, bin_pred(*i,value) != false, pred(*) != false. Return last if no such iterator is found.
Rationale:
This is request for a pure extension, so it is not a defect in the current standard. As the submitter pointed out, "this can be accomplished using a combination of find_if and bind_1st or bind_2nd".
Section: 22.2.1.3.2 [facet.ctype.char.members] Status: Dup Submitter: Dietmar Kühl Date: 2000-04-24
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Duplicate of: 28
Discussion:
The description of the is() member in paragraph 4 of 22.2.1.3.2 [facet.ctype.char.members] is broken: According to this description, the second form of the is() method modifies the masks in the ctype object. The correct semantics if, of course, to obtain an array of masks. The corresponding method in the general case, ie. the do_is() method as described in 22.2.1.1.2 [locale.ctype.virtuals] paragraph 1 does the right thing.
Proposed resolution:
Change paragraph 4 from
The second form, for all *p in the range [low, high), assigns vec[p-low] to table()[(unsigned char)*p].
to become
The second form, for all *p in the range [low, high), assigns table()[(unsigned char)*p] to vec[p-low].
Rationale:
Section: 25.1.5 [alg.find] Status: NAD Submitter: Andrew Koenig Date: 2000-05-02
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Discussion:
Is the following implementation of find acceptable?
template<class Iter, class X>
Iter find(Iter begin, Iter end, const X& x)
{
X x1 = x; // this is the crucial statement
while (begin != end && *begin != x1)
++begin;
return begin;
}
If the answer is yes, then it is implementation-dependent as to whether the following fragment is well formed:
vector<string> v;
find(v.begin(), v.end(), "foo");
At issue is whether there is a requirement that the third argument of find be CopyConstructible. There may be no problem here, but analysis is necessary.
Rationale:
There is no indication in the standard that find's third argument is required to be Copy Constructible. The LWG believes that no such requirement was intended. As noted above, there are times when a user might reasonably pass an argument that is not Copy Constructible.
Section: 24.5.1 [istream.iterator] Status: NAD Submitter: Andrew Koenig Date: 2000-05-02
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Discussion:
I do not think the standard specifies what operation(s) on istream iterators trigger input operations. So, for example:
istream_iterator<int> i(cin);
int n = *i++;
I do not think it is specified how many integers have been read from cin. The number must be at least 1, of course, but can it be 2? More?
Rationale:
The standard is clear as written: the stream is read every time operator++ is called, and it is also read either when the iterator is constructed or when operator* is called for the first time. In the example above, exactly two integers are read from cin.
There may be a problem with the interaction between istream_iterator and some STL algorithms, such as find. There are no guarantees about how many times find may invoke operator++.
Section: 23.1.4 [associative.reqmts] Status: Dup Submitter: Mark Rodgers Date: 2000-05-19
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Duplicate of: 233
Discussion:
Closed issue 192 raised several problems with the specification of this function, but was rejected as Not A Defect because it was too big a change with unacceptable impacts on existing implementations. However, issues remain that could be addressed with a smaller change and with little or no consequent impact.
The specification is inconsistent with the original proposal and with several implementations.
The initial implementation by Hewlett Packard only ever looked immediately before p, and I do not believe there was any intention to standardize anything other than this behavior. Consequently, current implementations by several leading implementors also look immediately before p, and will only insert after p in logarithmic time. I am only aware of one implementation that does actually look after p, and it looks before p as well. It is therefore doubtful that existing code would be relying on the behavior defined in the standard, and it would seem that fixing this defect as proposed below would standardize existing practice.
The specification is inconsistent with insertion for sequence containers.
This is difficult and confusing to teach to newcomers. All insert operations that specify an iterator as an insertion location should have a consistent meaning for the location represented by that iterator.
As specified, there is no way to hint that the insertion should occur at the beginning of the container, and the way to hint that it should occur at the end is long winded and unnatural.
For a container containing n elements, there are n+1 possible insertion locations and n+1 valid iterators. For there to be a one-to-one mapping between iterators and insertion locations, the iterator must represent an insertion location immediately before the iterator.
When appending sorted ranges using insert_iterators, insertions are guaranteed to be sub-optimal.
In such a situation, the optimum location for insertion is always immediately after the element previously inserted. The mechanics of the insert iterator guarantee that it will try and insert after the element after that, which will never be correct. However, if the container first tried to insert before the hint, all insertions would be performed in amortized constant time.
Proposed resolution:
In 23.1.2 [lib.associative.reqmts] paragraph 7, table 69, make the following changes in the row for a.insert(p,t):
assertion/note pre/post condition:
Change the last sentence from
"iterator p is a hint pointing to where the insert should start to search."
to
"iterator p is a hint indicating that immediately before p may be a correct location where the insertion could occur."
complexity:
Change the words "right after" to "immediately before".
Rationale:
Section: D.9.1 [auto.ptr] Status: NAD Submitter: Joseph Gottman Date: 2000-06-30
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Discussion:
According to section 20.4.5, the function auto_ptr::operator=() returns a reference to an auto_ptr. The reason that operator=() usually returns a reference is to facilitate code like
int x,y,z;
x = y = z = 1;
However, given analogous code for auto_ptrs,
auto_ptr<int> x, y, z;
z.reset(new int(1));
x = y = z;
the result would be that z and y would both be set to NULL, instead of all the auto_ptrs being set to the same value. This makes such cascading assignments useless and counterintuitive for auto_ptrs.
Proposed resolution:
Change auto_ptr::operator=() to return void instead of an auto_ptr reference.
Rationale:
The return value has uses other than cascaded assignments: a user can call an auto_ptr member function, pass the auto_ptr to a function, etc. Removing the return value could break working user code.
Section: 20.6.3 [base], 24.3.2 [iterator.basic] Status: NAD Submitter: Robert Dick Date: 2000-08-17
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Discussion:
According to the November 1997 Draft Standard, the results of deleting an object of a derived class through a pointer to an object of its base class are undefined if the base class has a non-virtual destructor. Therefore, it is potentially dangerous to publicly inherit from such base classes.
Defect:
The STL design encourages users to publicly inherit from a number of classes
which do nothing but specify interfaces, and which contain non-virtual
destructors.
Attribution:
Wil Evers and William E. Kempf suggested this modification for functional
objects.
Proposed resolution:
When a base class in the standard library is useful only as an interface specifier, i.e., when an object of the class will never be directly instantiated, specify that the class contains a protected destructor. This will prevent deletion through a pointer to the base class without performance, or space penalties (on any implementation I'm aware of).
As an example, replace...
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
};
... with...
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
protected:
~unary_function() {}
};
Affected definitions:
20.3.1 [lib.function.objects] -- unary_function, binary_function
24.3.2 [lib.iterator.basic] -- iterator
Rationale:
The standard is clear as written; this is a request for change, not a defect in the strict sense. The LWG had several different objections to the proposed change. One is that it would prevent users from creating objects of type unary_function and binary_function. Doing so can sometimes be legitimate, if users want to pass temporaries as traits or tag types in generic code.
Section: D.7.1.3 [depr.strstreambuf.virtuals] Status: NAD Submitter: Martin Sebor Date: 2000-10-05
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Discussion:
It appears that the interaction of the strstreambuf members overflow() and seekoff() can lead to undefined behavior in cases where defined behavior could reasonably be expected. The following program demonstrates this behavior:
#include <strstream>
int main ()
{
std::strstreambuf sb;
sb.sputc ('c');
sb.pubseekoff (-1, std::ios::end, std::ios::in);
return !('c' == sb.sgetc ());
}
D.7.1.1, p1 initializes strstreambuf with a call to basic_streambuf<>(), which in turn sets all pointers to 0 in 27.5.2.1, p1.
27.5.2.2.5, p1 says that basic_streambuf<>::sputc(c) calls overflow(traits::to_int_type(c)) if a write position isn't available (it isn't due to the above).
D.7.1.3, p3 says that strstreambuf::overflow(off, ..., ios::in) makes at least one write position available (i.e., it allows the function to make any positive number of write positions available).
D.7.1.3, p13 computes newoff = seekhigh - eback(). In D.7.1, p4 we see seekhigh = epptr() ? epptr() : egptr(), or seekhigh = epptr() in this case. newoff is then epptr() - eback().
D.7.1.4, p14 sets gptr() so that gptr() == eback() + newoff + off, or gptr() == epptr() + off holds.
If strstreambuf::overflow() made exactly one write position available then gptr() will be set to just before epptr(), and the program will return 0. Buf if the function made more than one write position available, epptr() and gptr() will both point past pptr() and the behavior of the program is undefined.
Proposed resolution:
Change the last sentence of D.7.1 [depr.strstreambuf] paragraph 4 from
Otherwise, seeklow equals gbeg and seekhigh is either pend, if pend is not a null pointer, or gend.
to become
Otherwise, seeklow equals gbeg and seekhigh is either gend if 0 == pptr(), or pbase() + max where max is the maximum value of pptr() - pbase() ever reached for this stream.
[ pre-Copenhagen: Dietmar provided wording for proposed resolution. ]
[ post-Copenhagen: Fixed a typo: proposed resolution said to fix 4.7.1, not D.7.1. ]
Rationale:
This is related to issue 65: it's not clear what it means to seek beyond the current area. Without resolving issue 65 we can't resolve this. As with issue 65, the library working group does not wish to invest time nailing down corner cases in a deprecated feature.
Section: 18.7 [support.exception] Status: NAD Submitter: J. Stephen Adamczyk Date: 2000-10-10
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Discussion:
One of our customers asks whether this is valid C++:
#include <cstdarg>
void bar(const char *, va_list);
void
foo(const char *file, const char *, ...)
{
va_list ap;
va_start(ap, file);
bar(file, ap);
va_end(ap);
}
The issue being whether it is valid to use cstdarg when the final parameter before the "..." is unnamed. cstdarg is, as far as I can tell, inherited verbatim from the C standard. and the definition there (7.8.1.1 in the ISO C89 standard) refers to "the identifier of the rightmost parameter". What happens when there is no such identifier?
My personal opinion is that this should be allowed, but some tweak might be required in the C++ standard.
Rationale:
Not a defect, the C and C++ standards are clear. It is impossible to use varargs if the parameter immediately before "..." has no name, because that is the parameter that must be passed to va_start. The example given above is broken, because va_start is being passed the wrong parameter.
There is no support for extending varargs to provide additional functionality beyond what's currently there. For reasons of C/C++ compatibility, it is especially important not to make gratuitous changes in this part of the C++ standard. The C committee has already been requested not to touch this part of the C standard unless necessary.
Section: 20.1.2 [allocator.requirements] Status: NAD Submitter: Matt Austern Date: 2000-11-07
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Discussion:
In 20.1.5, paragraph 5, the standard says that "Implementors are encouraged to supply libraries that can accept allocators that encapsulate more general memory models and that support non-equal instances." This is intended as normative encouragement to standard library implementors. However, it is possible to interpret this sentence as applying to nonstandard third-party libraries.
Proposed resolution:
In 20.1.5, paragraph 5, change "Implementors" to "Implementors of the library described in this International Standard".
Rationale:
The LWG believes the normative encouragement is already sufficiently clear, and that there are no important consequences even if it is misunderstood.
Section: 23.1 [container.requirements] Status: NAD Submitter: Steve Cleary Date: 2000-11-27
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Discussion:
This came from an email from Steve Cleary to Fergus in reference to issue 179. The library working group briefly discussed this in Toronto and believes it should be a separate issue.
Steve said: "We may want to state that the const/non-const iterators must have the same difference type, size_type, and category."
(Comment from Judy) I'm not sure if the above sentence should be true for all const and non-const iterators in a particular container, or if it means the container's iterator can't be compared with the container's const_iterator unless the above it true. I suspect the former.
Proposed resolution:
In Section: 23.1 [container.requirements], table 65, in the assertion/note pre/post condition for X::const_iterator, add the following:
typeid(X::const_iterator::difference_type) == typeid(X::iterator::difference_type)
typeid(X::const_iterator::size_type) == typeid(X::iterator::size_type)
typeid(X::const_iterator::category) == typeid(X::iterator::category)
Rationale:
Going through the types one by one: Iterators don't have a size_type. We already know that the difference types are identical, because the container requirements already say that the difference types of both X::iterator and X::const_iterator are both X::difference_type. The standard does not require that X::iterator and X::const_iterator have the same iterator category, but the LWG does not see this as a defect: it's possible to imagine cases in which it would be useful for the categories to be different.
It may be desirable to require X::iterator and X::const_iterator to have the same value type, but that is a new issue. (Issue 322.)
Section: 27.4.2.2 [fmtflags.state] Status: NAD Submitter: Judy Ward Date: 2000-12-30
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Discussion:
The Effects clause for ios_base::setf(fmtflags fmtfl) says "Sets fmtfl in flags()". What happens if the user first calls ios_base::scientific and then calls ios_base::fixed or vice-versa? This is an issue for all of the conflicting flags, i.e. ios_base::left and ios_base::right or ios_base::dec, ios_base::hex and ios_base::oct.
I see three possible solutions:
Most existing implementations that I tried seem to conform to resolution #3, except that when using the iomanip manipulator hex or oct then that always overrides dec, but calling setf(ios_base::hex) doesn't.
There is a sort of related issue, which is that although the ios_base constructor says that each ios_base member has an indeterminate value after construction, all the existing implementations I tried explicitly set ios_base::dec.
Proposed resolution:
Rationale:
adjustfield, basefield, and floatfield are each multi-bit fields. It is possible to set multiple bits within each of those fields. (For example, dec and oct). These fields are used by locale facets. The LWG reviewed the way in which each of those three fields is used, and believes that in each case the behavior is well defined for any possible combination of bits. See for example Table 58, in 22.2.2.2.2 [facet.num.put.virtuals], noting the requirement in paragraph 6 of that section.
Users are advised to use manipulators, or else use the two-argument version of setf, to avoid unexpected behavior.
Section: 26.7 [c.math] Status: NAD Submitter: Judy Ward Date: 2000-12-30
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Discussion:
In ISO/IEC 9899:1990 Programming Languages C we find the following concerning <math.h>:
7.13.4 Mathematics <math.h>
The names of all existing functions declared in the <math.h> header, suffixed with f or l, are reserved respectively for corresponding functions with float and long double arguments are return values.
For example, float sinf(float) is reserved.
In the C99 standard, <math.h> must contain declarations for these functions.
So, is it acceptable for an implementor to add these prototypes to the C++ versions of the math headers? Are they required?
Proposed resolution:
Add these Functions to Table 80, section 26.5 and to Table 99, section C.2:
acosf asinf atanf atan2f ceilf cosf coshf
expf fabsf floorf fmodf frexpf ldexpf
logf log10f modff powf sinf sinhf sqrtf
tanf tanhf
acosl asinl atanl atan2l ceill cosl coshl
expl fabsl floorl fmodl frexpl ldexpl
logl log10l modfl powl sinl sinhl sqrtl
tanl tanhl
There should probably be a note saying that these functions are optional and, if supplied, should match the description in the 1999 version of the C standard. In the next round of C++ standardization they can then become mandatory.
Rationale:
The C90 standard, as amended, already permits (but does not require) these functions, and the C++ standard incorporates the C90 standard by reference. C99 is not an issue, because it is never referred to by the C++ standard.
Section: 25.2.4 [alg.transform] Status: NAD Submitter: Angelika Langer Date: 2001-01-04
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Discussion:
This issue is related to issue 242. In case that the resolution proposed for issue 242 is accepted, we have have the following situation: The 4 numeric algorithms (accumulate and consorts) as well as transform would allow a certain category of side effects. The numeric algorithms specify that they invoke the functor "for every iterator i in the range [first, last) in order". transform, in contrast, would not give any guarantee regarding order of invocation of the functor, which means that the functor can be invoked in any arbitrary order.
Why would that be a problem? Consider an example: say the transformator that is a simple enumerator ( or more generally speaking, "is order-sensitive" ). Since a standard compliant implementation of transform is free to invoke the enumerator in no definite order, the result could be a garbled enumeration. Strictly speaking this is not a problem, but it is certainly at odds with the prevalent understanding of transform as an algorithms that assigns "a new _corresponding_ value" to the output elements.
All implementations that I know of invoke the transformator in definite order, namely starting from first and proceeding to last - 1. Unless there is an optimization conceivable that takes advantage of the indefinite order I would suggest to specify the order, because it eliminate the uncertainty that users would otherwise have regarding the order of execution of their potentially order-sensitive function objects.
Proposed resolution:
In section 25.2.3 - Transform [lib.alg.transform] change:
-1- Effects: Assigns through every iterator i in the range [result, result + (last1 - first1)) a new corresponding value equal to op(*(first1 + (i - result)) or binary_op(*(first1 + (i - result), *(first2 + (i - result))).
to:
-1- Effects: Computes values by invoking the operation op or binary_op for every iterator in the range [first1, last1) in order. Assigns through every iterator i in the range [result, result + (last1 - first1)) a new corresponding value equal to op(*(first1 + (i - result)) or binary_op(*(first1 + (i - result), *(first2 + (i - result))).
Rationale:
For Input Iterators an order is already guaranteed, because only one order is possible. If a user who passes a Forward Iterator to one of these algorithms really needs a specific order of execution, it's possible to achieve that effect by wrapping it in an Input Iterator adaptor.
Section: 20.2.3 [pairs] Status: NAD Submitter: Martin Sebor Date: 2001-01-14
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Discussion:
The synopsis of the header <utility> in 20.2 [utility] lists the complete set of equality and relational operators for pair but the section describing the template and the operators only describes operator==() and operator<(), and it fails to mention any requirements on the template arguments. The remaining operators are not mentioned at all.
Rationale:
20.2.1 [operators] paragraph 10 already specifies the semantics. That paragraph says that, if declarations of operator!=, operator>, operator<=, and operator>= appear without definitions, they are defined as specified in 20.2.1 [operators]. There should be no user confusion, since that paragraph happens to immediately precede the specification of pair.
Section: 22.2.1.5 [locale.codecvt.byname] Status: NAD Submitter: Gregory Bumgardner Date: 2001-01-25
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Discussion:
The effects of codecvt<>::do_length() are described in 22.2.1.5.2, paragraph 10. As implied by that paragraph, and clarified in issue 75, codecvt<>::do_length() must process the source data and update the stateT argument just as if the data had been processed by codecvt<>::in(). However, the standard does not specify how do_length() would report a translation failure, should the source sequence contain untranslatable or illegal character sequences.
The other conversion methods return an "error" result value to indicate that an untranslatable character has been encountered, but do_length() already has a return value (the number of source characters that have been processed by the method).
Proposed resolution:
This issue cannot be resolved without modifying the interface. An exception cannot be used, as there would be no way to determine how many characters have been processed and the state object would be left in an indeterminate state.
A source compatible solution involves adding a fifth argument to length() and do_length() that could be used to return position of the offending character sequence. This argument would have a default value that would allow it to be ignored:
int length(stateT& state,
const externT* from,
const externT* from_end,
size_t max,
const externT** from_next = 0);
virtual
int do_length(stateT& state,
const externT* from,
const externT* from_end,
size_t max,
const externT** from_next);
Then an exception could be used to report any translation errors and the from_next argument, if used, could then be used to retrieve the location of the offending character sequence.
Rationale:
The standard is already clear: the return value is the number of "valid complete characters". If it encounters an invalid sequence of external characters, it stops.
Section: 24.1 [iterator.requirements] Status: NAD Submitter: Dave Abrahams Date: 2001-02-05
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Discussion:
We all "know" that input iterators are allowed to produce values when dereferenced of which there is no other in-memory copy.
But: Table 72, with a careful reading, seems to imply that this can only be the case if the value_type has no members (e.g. is a built-in type).
The problem occurs in the following entry:
a->m pre: (*a).m is well-defined
Equivalent to (*a).m
*a.m can be well-defined if *a is not a reference type, but since operator->() must return a pointer for a->m to be well-formed, it needs something to return a pointer to. This seems to indicate that *a must be buffered somewhere to make a legal input iterator.
I don't think this was intentional.
Rationale:
The current standard is clear and consistent. Input iterators that return rvalues are in fact implementable. They may in some cases require extra work, but it is still possible to define an operator-> in such cases: it doesn't have to return a T*, but may return a proxy type. No change to the standard is justified.
Section: 18.7.3.3 [terminate] Status: NAD Submitter: Judy Ward Date: 2001-04-03
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Discussion:
According to section 18.7.3.3 of the standard, std::terminate() is supposed to call the terminate_handler in effect immediately after evaluating the throw expression.
Question: what if the terminate_handler in effect is itself std::terminate?
For example:
#include <exception>
int main () {
std::set_terminate(std::terminate);
throw 5;
return 0;
}
Is the implementation allowed to go into an infinite loop?
I think the same issue applies to std::set_unexpected.
Proposed resolution:
Rationale:
Infinite recursion is to be expected: users who set the terminate handler to terminate are explicitly asking for terminate to call itself.
Section: 18.7.3.3 [terminate] Status: NAD Submitter: Detlef Vollmann Date: 2001-04-11
View all other issues in [terminate].
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Discussion:
The standard appears to contradict itself about whether the stack is unwound when the implementation calls terminate().
From 18.7.3.3p2:
Calls the terminate_handler function in effect immediately after evaluating the throw-expression (lib.terminate.handler), if called by the implementation [...]
So the stack is guaranteed not to be unwound.
But from 15.3p9:
[...]whether or not the stack is unwound before this call to terminate() is implementation-defined (except.terminate).
And 15.5.1 actually defines that in most cases the stack is unwound.
Proposed resolution:
Rationale:
There is definitely no contradiction between the core and library clauses; nothing in the core clauses says that stack unwinding happens after terminate is called. 18.7.3.3p2 does not say anything about when terminate() is called; it merely specifies which terminate_handler is used.
Section: 26.7 [c.math] Status: NAD Submitter: Dave Abrahams Date: 2001-06-04
View all other issues in [c.math].
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Discussion:
Currently the standard mandates the following overloads of abs():
abs(long), abs(int) in <cstdlib>
abs(float), abs(double), abs(long double) in <cmath>
template<class T> T abs(const complex<T>&) in <complex>
template<class T> valarray<T> abs(const valarray<T>&); in <valarray>
The problem is that having only some overloads visible of a function that works on "implicitly inter-convertible" types is dangerous in practice. The headers that get included at any point in a translation unit can change unpredictably during program development/maintenance. The wrong overload might be unintentionally selected.
Currently, there is nothing that mandates the simultaneous visibility of these overloads. Indeed, some vendors have begun fastidiously reducing dependencies among their (public) headers as a QOI issue: it helps people to write portable code by refusing to compile unless all the correct headers are #included.
The same issue may exist for other functions in the library.
Redmond: PJP reports that C99 adds two new kinds of abs: complex, and int_max_abs.
Related issue: 343.
[ Bellevue: ]
The situation is not sufficiently severe to warrant a change.
Rationale:
The programs that could potentially be broken by this situation are already fragile, and somewhat contrived: For example, a user-defined class that has conversion overloads both to long and to float. If x is a value of such a class, then abs(x) would give the long version if the user included <cstdlib>, the float version if the user included <cmath>, and would be diagnosed as ambiguous at compile time if the user included both headers. The LWG couldn't find an example of a program whose meaning would be changed (as opposed to changing it from well-formed to ill-formed) simply by adding another standard header.
Since the harm seems minimal, and there don't seem to be any simple and noninvasive solutions, this is being closed as NAD. It is marked as "Future" for two reasons. First, it might be useful to define an <all> header that would include all Standard Library headers. Second, we should at least make sure that future library extensions don't make this problem worse.
Section: 22.2.6.4 [locale.moneypunct.byname] Status: NAD Submitter: Martin Sebor Date: 2001-07-05
View all issues with NAD status.
Discussion:
The definition of the moneypunct facet contains the typedefs char_type and string_type. Only one of these names, string_type, is defined in the derived facet, moneypunct_byname.
Proposed resolution:
For consistency with the numpunct facet, add a typedef for char_type to the definition of the moneypunct_byname facet in 22.2.6.4 [locale.moneypunct.byname].
Rationale:
The absence of the typedef is irrelevant. Users can still access the typedef, because it is inherited from the base class.
Section: 22.1.1 [locale] Status: NAD Submitter: Martin Sebor Date: 2001-07-15
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Discussion:
The "exposition only" value of the std::locale::none constant shown in the definition of class locale is misleading in that it on many systems conflicts with the value assigned to one if the LC_XXX constants (specifically, LC_COLLATE on AIX, LC_ALL on HP-UX, LC_CTYPE on Linux and SunOS). This causes incorrect behavior when such a constant is passed to one of the locale member functions that accept a locale::category argument and interpret it as either the C LC_XXX constant or a bitmap of locale::category values. At least three major implementations adopt the suggested value without a change and consequently suffer from this problem.
For instance, the following code will (presumably) incorrectly copy facets belonging to the collate category from the German locale on AIX:
std::locale l (std::locale ("C"), "de_DE", std::locale::none);
Rationale:
The LWG agrees that it may be difficult to implement locale member functions in such a way that they can take either category arguments or the LC_ constants defined in <cctype>. In light of this requirement (22.1.1.1.1 [locale.category], paragraph 2), and in light of the requirement in the preceding paragraph that it is possible to combine category bitmask elements with bitwise operations, defining the category elements is delicate, particularly if an implementor is constrained to work with a preexisting C library. (Just using the existing LC_ constants would not work in general.) There's no set of "exposition only" values that could give library implementors proper guidance in such a delicate matter. The non-normative example we're giving is no worse than any other choice would be.
See issue 347.
Section: 27.4.3 [fpos] Status: NAD Submitter: PremAnand M. Rao Date: 2001-08-27
View all other issues in [fpos].
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Discussion:
Increment and decrement operators are missing from Table 88 -- Position type requirements in 27.4.3 [fpos].
Proposed resolution:
Table 88 (section 27.4.3) -- Position type requirements be updated to include increment and decrement operators.
expression return type operational note
++p fpos& p += O(1)
p++ fpos { P tmp = p;
++p;
return tmp; }
--p fpos& p -= O(1)
p-- fpos { P tmp = p;
--p;
return tmp; }
Rationale:
The LWG believes this is a request for extension, not a defect report. Additionally, nobody saw a clear need for this extension; fpos is used only in very limited ways.
Section: 22.2.2 [category.numeric] Status: NAD Submitter: Howard Hinnant Date: 2001-10-13
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Discussion:
When both grouping and showbase are active and the basefield is octal, does the leading 0 participate in the grouping or not? For example, should one format as: 0,123,456 or 0123,456?
An analogy can be drawn with hexadecimal. It appears that 0x123,456 is preferred over 0x,123,456. However, this analogy is not universally accepted to apply to the octal base. The standard is not clear on how to format (or parse) in this manner.
Proposed resolution:
Insert into 22.2.3.1.2 [facet.numpunct.virtuals] paragraph 3, just before the last sentence:
The leading hexadecimal base specifier "0x" does not participate in grouping. The leading '0' octal base specifier may participate in grouping. It is unspecified if the leading '0' participates in formatting octal numbers. In parsing octal numbers, the implementation is encouraged to accept both the leading '0' participating in the grouping, and not participating (e.g. 0123,456 or 0,123,456).
Rationale:
The current behavior may be unspecified, but it's not clear that it matters. This is an obscure corner case, since grouping is usually intended for the benefit of humans and oct/hex prefixes are usually intended for the benefit of machines. There is not a strong enough consensus in the LWG for action.
Section: 20.2.3 [pairs] Status: Dup Submitter: Andy Sawyer Date: 2001-10-23
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Duplicate of: 532
Discussion:
The current wording of 20.2.2 [lib.pairs] p6 precludes the use of operator< on any pair type which contains a pointer.
Proposed resolution:
In 20.2.3 [pairs] paragraph 6, replace:
Returns: x.first < y.first || (!(y.first < x.first) && x.second <
y.second).
With:
Returns: std::less<T1>()( x.first, y.first ) ||
(!std::less<T1>()( y.first, x.first) &&
std::less<T2>()( x.second, y.second ) )
Rationale:
This is an instance of a much more general problem. If we want operator< to translate to std::less for pairs of pointers, where do we draw the line? The same issue applies to individual pointers, smart pointer wrappers, std::vector<T*>, and so on.
Andy Koenig suggests that the real issue here is that we aren't distinguishing adequately between two different orderings, a "useful ordering" and a "canonical ordering" that's used just because we sometimes need some ordering without caring much which ordering it is. Another example of the later is typeinfo's before.
Section: 20.7.5.1 [allocator.members], 20.1.2 [allocator.requirements], 17.4.1.1 [contents] Status: Dup Submitter: Nathan Myers Date: 2001-10-25
View all other issues in [allocator.members].
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Duplicate of: 634
Discussion:
See c++std-lib-9006 and c++std-lib-9007. This issue is taken verbatim from -9007.
The core language feature allowing definition of operator&() applied to any non-builtin type makes that operator often unsafe to use in implementing libraries, including the Standard Library. The result is that many library facilities fail for legal user code, such as the fragment
class A { private: A* operator&(); };
std::vector<A> aa;
class B { };
B* operator&(B&) { return 0; }
std::vector<B> ba;
In particular, the requirements table for Allocator (Table 32) specifies no semantics at all for member address(), and allocator<>::address is defined in terms of unadorned operator &.
Proposed resolution:
In 20.6.1.1, Change the definition of allocator<>::address from:
Returns: &x
to:
Returns: The value that the built in operator&(x) would return if not overloaded.
In 20.1.6, Table 32, add to the Notes column of the a.address(r) and a.address(s) lines, respectively:
allocator<T>::address(r) allocator<T>::address(s)
In addition, in clause 17.4.1.1, add a statement:
The Standard Library does not apply operator& to any type for which operator& may be overloaded.
Rationale:
The LWG believes both examples are ill-formed. The contained type is required to be CopyConstructible (20.1.1 [utility.arg.requirements]), and that includes the requirement that &t return the usual types and values. Since allocators are intended to be used in conjunction with containers, and since the CopyConstructible requirements appear to have been written to deal with the concerns of this issue, the LWG feels it is NAD unless someone can come up with a well-formed example exhibiting a problem.
It may well be that the CopyConstructible requirements are too restrictive and that either the container requirements or the CopyConstructive requirements should be relaxed, but that's a far larger issue. Marking this issue as "future" as a pointer to that larger issue.
Section: 20.6 [function.objects] Status: NAD Editorial Submitter: Dale Riley Date: 2001-11-12
View all other issues in [function.objects].
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Discussion:
In 20.6 [function.objects] the header <functional> synopsis declares the unary_negate and binary_negate function objects as struct. However in 20.6.10 [negators] the unary_negate and binary_negate function objects are defined as class. Given the context, they are not "basic function objects" like negate, so this is either a typo or an editorial oversight.
[Taken from comp.std.c++]
Proposed resolution:
Change the synopsis to reflect the useage in 20.6.10 [negators]
[Curaçao: Since the language permits "struct", the LWG views this as NAD. They suggest, however, that the Project Editor might wish to make the change as editorial.]
Section: 20.2.3 [pairs] Status: NAD Editorial Submitter: Martin Sebor Date: 2001-12-02
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Discussion:
The class template std::pair defines a template ctor (20.2.2, p4) but no template assignment operator. This may lead to inefficient code since assigning an object of pair<C, D> to pair<A, B> where the types C and D are distinct from but convertible to A and B, respectively, results in a call to the template copy ctor to construct an unnamed temporary of type pair<A, B> followed by an ordinary (perhaps implicitly defined) assignment operator, instead of just a straight assignment.
Proposed resolution:
Add the following declaration to the definition of std::pair:
template<class U, class V>
pair& operator=(const pair<U, V> &p);
And also add a paragraph describing the effects of the function template to the end of 20.2.2:
template<class U, class V>
pair& operator=(const pair<U, V> &p);
Effects: first = p.first; second = p.second; Returns: *this
[Curaçao: There is no indication this is was anything other than a design decision, and thus NAD. May be appropriate for a future standard.]
[ Pre Bellevue: It was recognized that this was taken care of by N1856, and thus moved from NAD Future to NAD Editorial. ]
Section: 22.2.1 [category.ctype] Status: NAD Submitter: Matt Austern Date: 2002-01-23
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Discussion:
What should the following program print?
#include <locale>
#include <iostream>
class my_ctype : public std::ctype<char>
{
typedef std::ctype<char> base;
public:
my_ctype(std::size_t refs = 0) : base(my_table, false, refs)
{
std::copy(base::classic_table(), base::classic_table() + base::table_size,
my_table);
my_table[(unsigned char) '_'] = (base::mask) (base::print | base::space);
}
private:
mask my_table[base::table_size];
};
int main()
{
my_ctype ct;
std::cout << "isspace: " << ct.is(std::ctype_base::space, '_') << " "
<< "isalpha: " << ct.is(std::ctype_base::alpha, '_') << std::endl;
}
The goal is to create a facet where '_' is treated as whitespace.
On gcc 3.0, this program prints "isspace: 1 isalpha: 0". On Microsoft C++ it prints "isspace: 1 isalpha: 1".
I believe that both implementations are legal, and the standard does not give enough guidance for users to be able to use std::ctype's protected interface portably.
The above program assumes that ctype_base::mask enumerators like space and print are disjoint, and that the way to say that a character is both a space and a printing character is to or those two enumerators together. This is suggested by the "exposition only" values in 22.2.1 [category.ctype], but it is nowhere specified in normative text. An alternative interpretation is that the more specific categories subsume the less specific. The above program gives the results it does on the Microsoft compiler because, on that compiler, print has all the bits set for each specific printing character class.
From the point of view of std::ctype's public interface, there's no important difference between these two techniques. From the point of view of the protected interface, there is. If I'm defining a facet that inherits from std::ctype<char>, I'm the one who defines the value that table()['a'] returns. I need to know what combination of mask values I should use. This isn't so very esoteric: it's exactly why std::ctype has a protected interface. If we care about users being able to write their own ctype facets, we have to give them a portable way to do it.
Related reflector messages: lib-9224, lib-9226, lib-9229, lib-9270, lib-9272, lib-9273, lib-9274, lib-9277, lib-9279.
Issue 339 is related, but not identical. The proposed resolution if issue 339 says that ctype_base::mask must be a bitmask type. It does not say that the ctype_base::mask elements are bitmask elements, so it doesn't directly affect this issue.
More comments from Benjamin Kosnik, who believes that that C99 compatibility essentially requires what we're calling option 1 below.
I think the C99 standard is clear, that isspace -> !isalpha.
--------
#include <locale>
#include <iostream>
class my_ctype : public std::ctype<char>
{
private:
typedef std::ctype<char> base;
mask my_table[base::table_size];
public:
my_ctype(std::size_t refs = 0) : base(my_table, false, refs)
{
std::copy(base::classic_table(), base::classic_table() + base::table_size,
my_table);
mask both = base::print | base::space;
my_table[static_cast<mask>('_')] = both;
}
};
int main()
{
using namespace std;
my_ctype ct;
cout << "isspace: " << ct.is(ctype_base::space, '_') << endl;
cout << "isprint: " << ct.is(ctype_base::print, '_') << endl;
// ISO C99, isalpha iff upper | lower set, and !space.
// 7.5, p 193
// -> looks like g++ behavior is correct.
// 356 -> bitmask elements are required for ctype_base
// 339 -> bitmask type required for mask
cout << "isalpha: " << ct.is(ctype_base::alpha, '_') << endl;
}
Proposed resolution:
Informally, we have three choices:
Either of the first two options is just as good from the standpoint of portability. Either one will require some implementations to change.
Rationale:
The LWG agrees that this is a real ambiguity, and that both interpretations are conforming under the existing standard. However, there's no evidence that it's causing problems for real users. Users who want to define ctype facets portably can test the ctype_base masks to see which interpretation is being used.
Section: 26.7 [c.math] Status: NAD Editorial Submitter: Ray Lischner Date: 2002-02-26
View all other issues in [c.math].
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Discussion:
The float versions of the math functions have no meaningful value to return for a range error. The long double versions have a value they can return, but it isn't necessarily the most reasonable value.
Section 26.5 [lib.c.math], paragraph 5, says that C++ "adds float and long double overloaded versions of these functions, with the same semantics," referring to the math functions from the C90 standard.
The C90 standard, in section 7.5.1, paragraph 3, says that functions return "the value of the macro HUGE_VAL" when they encounter a range error. Section 7.5, paragraph 2, defines HUGE_VAL as a macro that "expands to a positive double expression, not necessarily representable as a float."
Therefore, the float versions of the math functions have no way to signal a range error. [Curaçao: The LWG notes that this isn't strictly correct, since errno is set.] The semantics require that they return HUGE_VAL, but they cannot because HUGE_VAL might not be representable as a float.
The problem with long double functions is less severe because HUGE_VAL is representable as a long double. On the other hand, it might not be a "huge" long double value, and might fall well within the range of normal return values for a long double function. Therefore, it does not make sense for a long double function to return a double (HUGE_VAL) for a range error.
Proposed resolution:
Curaçao: C99 was faced with a similar problem, which they fixed by adding HUGE_VALF and HUGE_VALL in addition to HUGE_VAL.
C++ must also fix, but it should be done in the context of the general C99 based changes to C++, not via DR. Thus the LWG in Curaçao felt the resolution should be NAD, FUTURE, but the issue is being held open for one more meeting to ensure LWG members not present during the discussion concur.
Rationale:
Will be fixed as part of more general work in the TR.
Section: 22.2.2.2.2 [facet.num.put.virtuals] Status: NAD Submitter: Martin Sebor Date: 2002-03-12
View all other issues in [facet.num.put.virtuals].
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Discussion:
22.2.2.2.2, p12 specifies that thousands_sep is to be inserted only for integral types (issue 282 suggests that this should be done for all arithmetic types).
22.2.2.1.2, p12 requires that grouping be checked for all extractors including that for void*.
I don't think that's right. void* values should not be checked for grouping, should they? (Although if they should, then num_put needs to write them out, otherwise their extraction will fail.)
Proposed resolution:
Change the first sentence of 22.2.2.2.2, p12 from
Digit grouping is checked. That is, the positions of discarded separators is examined for consistency with use_facet<numpunct<charT> >(loc).grouping(). If they are not consistent then ios_base::failbit is assigned to err.
to
Except for conversions to void*, digit grouping is checked...
Rationale:
This would be a change: as it stands, the standard clearly specifies that grouping applies to void*. A survey of existing practice shows that most existing implementations do that, as they should.
Section: 27 [input.output] Status: NAD Submitter: Walter Brown, Marc Paterno Date: 2002-05-10
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Discussion:
The following member functions are declared const, yet return non-const pointers. We believe they are should be changed, because they allow code that may surprise the user. See document N1360 for details and rationale.
[Santa Cruz: the real issue is that we've got const member functions that return pointers to non-const, and N1360 proposes replacing them by overloaded pairs. There isn't a consensus about whether this is a real issue, since we've never said what our constness policy is for iostreams. N1360 relies on a distinction between physical constness and logical constness; that distinction, or those terms, does not appear in the standard.]
Proposed resolution:
In 27.4.4 and 27.4.4.2
Replace
basic_ostream<charT,traits>* tie() const;
with
basic_ostream<charT,traits>* tie(); const basic_ostream<charT,traits>* tie() const;
and replace
basic_streambuf<charT,traits>* rdbuf() const;
with
basic_streambuf<charT,traits>* rdbuf(); const basic_streambuf<charT,traits>* rdbuf() const;
In 27.5.2 and 27.5.2.3.1
Replace
char_type* eback() const;
with
char_type* eback(); const char_type* eback() const;
Replace
char_type gptr() const;
with
char_type* gptr(); const char_type* gptr() const;
Replace
char_type* egptr() const;
with
char_type* egptr(); const char_type* egptr() const;
In 27.5.2 and 27.5.2.3.2
Replace
char_type* pbase() const;
with
char_type* pbase(); const char_type* pbase() const;
Replace
char_type* pptr() const;
with
char_type* pptr(); const char_type* pptr() const;
Replace
char_type* epptr() const;
with
char_type* epptr(); const char_type* epptr() const;
In 27.7.2, 27.7.2.2, 27.7.3 27.7.3.2, 27.7.4, and 27.7.6
Replace
basic_stringbuf<charT,traits,Allocator>* rdbuf() const;
with
basic_stringbuf<charT,traits,Allocator>* rdbuf(); const basic_stringbuf<charT,traits,Allocator>* rdbuf() const;
In 27.8.1.5, 27.8.1.7, 27.8.1.8, 27.8.1.10, 27.8.1.11, and 27.8.1.13
Replace
basic_filebuf<charT,traits>* rdbuf() const;
with
basic_filebuf<charT,traits>* rdbuf(); const basic_filebuf<charT,traits>* rdbuf() const;
Rationale:
The existing specification is a bit sloppy, but there's no particular reason to change this other than tidiness, and there are a number of ways in which streams might have been designed differently if we were starting today. There's no evidence that the existing constness policy is harming users. We might consider a different constness policy as part of a full stream redesign.
Section: 25.2.8 [alg.remove] Status: NAD Submitter: Anthony Williams Date: 2002-05-13
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Discussion:
remove_copy and remove_copy_if (25.2.8 [alg.remove]) permit their input range to be marked with Input Iterators. However, since two operations are required against the elements to copy (comparison and assigment), when the input range uses Input Iterators, a temporary copy must be taken to avoid dereferencing the iterator twice. This therefore requires the value type of the InputIterator to be CopyConstructible. If the iterators are at least Forward Iterators, then the iterator can be dereferenced twice, or a reference to the result maintained, so the temporary is not required.
Proposed resolution:
Add "If InputIterator does not meet the requirements of forward iterator, then the value type of InputIterator must be copy constructible. Otherwise copy constructible is not required." to 25.2.8 [alg.remove] paragraph 6.
Rationale:
The assumption is that an input iterator can't be dereferenced twice. There's no basis for that assumption in the Standard.
Section: 21.3.6.6 [string::replace] Status: NAD Editorial Submitter: Beman Dawes Date: 2002-06-03
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Discussion:
21.3.6.6 [string::replace] basic_string::replace, second signature, given in paragraph 1, has two "Throws" paragraphs (3 and 5).
In addition, the second "Throws" paragraph (5) includes specification (beginning with "Otherwise, the function replaces ...") that should be part of the "Effects" paragraph.
Proposed resolution:
Rationale:
This is editorial. Both "throws" statements are true. The bug is just that the second one should be a sentence, part of the "Effects" clause, not a separate "Throws". The project editor has been notified.
Section: 17.4.4.9 [res.on.exception.handling], 18.6.1 [type.info] Status: NAD Submitter: Randy Maddox Date: 2002-07-22
View all other issues in [res.on.exception.handling].
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Discussion:
Paragraph 3 under clause 17.4.4.9 [res.on.exception.handling], Restrictions on Exception Handling, states that "Any other functions defined in the C++ Standard Library that do not have an exception-specification may throw implementation-defined exceptions unless otherwise specified." This statement is followed by a reference to footnote 178 at the bottom of that page which states, apparently in reference to the C++ Standard Library, that "Library implementations are encouraged (but not required) to report errors by throwing exceptions from (or derived from) the standard exceptions."
These statements appear to be in direct contradiction to clause 18.6.1 [type.info], which states "The class exception defines the base class for the types of objects thrown as exceptions by the C++ Standard library components ...".
Is this inconsistent?
Proposed resolution:
Rationale:
Clause 17 is setting the overall library requirements, and it's clear and consistent. This sentence from Clause 18 is descriptive, not setting a requirement on any other class.
Section: 22.2.6.3.1 [locale.moneypunct.members], 22.2.6.3.2 [locale.moneypunct.virtuals] Status: NAD Submitter: Ray Lischner Date: 2002-08-08
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Discussion:
In section 22.2.6.3.1 [locale.moneypunct.members], frac_digits() returns type "int". This implies that frac_digits() might return a negative value, but a negative value is nonsensical. It should return "unsigned".
Similarly, in section 22.2.6.3.2 [locale.moneypunct.virtuals], do_frac_digits() should return "unsigned".
Proposed resolution:
Rationale:
Regardless of whether the return value is int or unsigned, it's always conceivable that frac_digits might return a nonsensical value. (Is 4294967295 really any better than -1?) The clients of moneypunct, the get and put facets, can and do perform range checks.
Section: 21.3.6.4 [string::insert] Status: NAD Submitter: Ray Lischner Date: 2002-08-16
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Discussion:
Section 21.3.6.4 [string::insert], paragraph 4, contains the following, "Then throws length_error if size() >= npos - rlen."
Related to DR 83, this sentence should probably be removed.
Proposed resolution:
Rationale:
This requirement is redundant but correct. No change is needed.
Section: 22.1.1 [locale] Status: Dup Submitter: Martin Sebor Date: 2002-09-06
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Duplicate of: 31
Discussion:
I think there is a problem with 22.1.1, p6 which says that
-6- An instance of locale is immutable; once a facet reference
is obtained from it, that reference remains usable as long
as the locale value itself exists.
and 22.1.1.2, p4:
const locale& operator=(const locale& other) throw();
-4- Effects: Creates a copy of other, replacing the current value.
How can a reference to a facet obtained from a locale object remain valid after an assignment that clearly must replace all the facets in the locale object? Imagine a program such as this
std::locale loc ("de_DE");
const std::ctype<char> &r0 = std::use_facet<std::ctype<char> >(loc);
loc = std::locale ("en_US");
const std::ctype<char> &r1 = std::use_facet<std::ctype<char> >(loc);
Is r0 really supposed to be preserved and destroyed only when loc goes out of scope?
Proposed resolution:
[Summer '04 mid-meeting mailing: Martin and Dietmar believe this is a duplicate of issue 31 and recommend that it be closed. ]
Section: 17 [library] Status: NAD Submitter: Matt Austern Date: 2002-10-23
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Discussion:
Many function templates have parameters that are passed by value; a typical example is find_if's pred parameter in 25.1.5 [alg.find]. Are the corresponding template parameters (Predicate in this case) implicitly required to be CopyConstructible, or does that need to be spelled out explicitly?
This isn't quite as silly a question as it might seem to be at first sight. If you call find_if in such a way that template argument deduction applies, then of course you'll get call by value and you need to provide a copy constructor. If you explicitly provide the template arguments, however, you can force call by reference by writing something like find_if<my_iterator, my_predicate&>. The question is whether implementation are required to accept this, or whether this is ill-formed because my_predicate& is not CopyConstructible.
The scope of this problem, if it is a problem, is unknown. Function object arguments to generic algorithms in clauses 25 [algorithms] and 26 [numerics] are obvious examples. A review of the whole library is necessary.
[ This is really two issues. First, predicates are typically passed by value but we don't say they must be Copy Constructible. They should be. Second: is specialization allowed to transform value arguments into references? References aren't copy constructible, so this should not be allowed. ]
[ 2007-01-12, Howard: First, despite the note above, references are copy constructible. They just aren't assignable. Second, this is very closely related to 92 and should be consistent with that. That issue already says that implementations are allowed to copy function objects. If one passes in a reference, it is copyable, but susceptible to slicing if one passes in a reference to a base. Third, with rvalue reference in the language one only needs to satisfy MoveConstructible to pass an rvalue "by value". Though the function might still copy the function object internally (requiring CopyConstructible). Finally (and fwiw), if we wanted to, it is easy to code all of the std::algorithms such that they do not copy function objects internally. One merely passes them by reference internally if desired (this has been fully implemented and shipped for several years). If this were mandated, it would reverse 92, allowing function objects to reliably maintain state. E.g. the example in 92 would reliably remove only the third element. ]
Proposed resolution:
Recommend NAD.
Rationale:
Generic algorithms will be marked with concepts and these will imply a requirement of MoveConstructible (not CopyConstructible). The signature of the function will then precisely describe and enforce the precise requirements.
Section: 26.3 [complex.numbers] Status: NAD Submitter: Gabriel Dos Reis Date: 2002-11-08
View all other issues in [complex.numbers].
View all issues with NAD status.
Discussion:
Practice with std::complex<> and the associative containers occasionally reveals artificial and distracting issues with constructs resembling: std::set<std::complex<double> > s;
The main reason for the above to fail is the absence of an approriate definition for std::less<std::complex<T> >. That in turn comes from the definition of the primary template std::less<> in terms of operator<.
The usual argument goes as follows: Since there is no ordering over the complex field compatible with field operations it makes little sense to define a function operator< operating on the datatype std::complex<T>. That is fine. However, that reasoning does not carry over to std::less<T> which is used, among other things, by associative containers as an ordering useful to meet complexity requirements.
Related issue: 348.
[ Pre Bellevue: Reopened at the request of Alisdair. ]
[ Bellevue: ]
This is a request for a design change, and not a defect in the standard. It is in scope to consider, but the group feels that it is not a change that we need to do. Is there a total ordering for floating point values, including NaN? There is not a clear enough solution or big enough problem for us to solve. Solving this problem would require solving the problem for floating point, which is equally unclear. The LWG noted that users who want to put objects into an associative container for which operator< isn't defined can simply provide their own comparison function object. NAD
Proposed resolution:
Informally: Add a specialization of std::less for std::complex.
Rationale:
Discussed in Santa Cruz. An overwhelming majority of the LWG believes this should not be treated a DR: it's a request for a design change, not a defect in the existing standard. Most people (10-3) believed that we probably don't want this change, period: as with issue 348, it's hard to know where to draw the line. The LWG noted that users who want to put objects into an associative container for which operator< isn't defined can simply provide their own comparison function object.
Section: 20.1.1 [utility.arg.requirements] Status: NAD Editorial Submitter: Doug Gregor Date: 2002-10-24
View other active issues in [utility.arg.requirements].
View all other issues in [utility.arg.requirements].
View all issues with NAD Editorial status.
Discussion:
The CopyConstructible requirements in Table 30 state that for an object t of type T (where T is CopyConstructible), the expression &t returns the address of t (with type T*). This requirement is overly strict, in that it disallows types that overload operator& to not return a value of type T*. This occurs, for instance, in the Boost.Lambda library, where operator& is overloaded for a Boost.Lambda function object to return another function object.
Example:
std::vector<int> u, v; int x; // ... std::transform(u.begin(), u.end(), std::back_inserter(v), _1 * x);
_1 * x returns an unnamed function object with operator& overloaded to not return T* , therefore rendering the std::transform call ill-formed. However, most standard library implementations will compile this code properly, and the viability of such binder libraries is severely hindered by the unnecessary restriction in the CopyConstructible requirements.
For reference, the address of an object can be retrieved without using the address-of operator with the following function template:
template <typename T> T* addressof(T& v)
{
return reinterpret_cast<T*>(
&const_cast<char&>(reinterpret_cast<const volatile char &>(v)));
}
Note: this relates directly to library issue 350, which will need to be reexamined if the CopyConstructible requirements change.
Proposed resolution:
Remove the last two rows of Table 30, eliminating the requirements that &t and &u return the address of t and u, respectively.
Rationale:
This was a deliberate design decision. Perhaps it should be reconsidered for C++0x.
Section: 24.1.1 [input.iterators] Status: NAD Submitter: Corwin Joy Date: 2002-12-11
View all other issues in [input.iterators].
View all issues with NAD status.
Discussion:
In section 24.1.1 [input.iterators] table 72 - 'Input Iterator Requirements' we have as a postcondition of *a: "If a==b and (a, b) is in the domain of == then *a is equivalent to *b".
In section 24.5.3.5 [istreambuf.iterator::equal] it states that "istreambuf_iterator::equal returns true if and only if both iterators are at end-of-stream, or neither is at end-of-stream, regardless of what streambuf object they use." (My emphasis).
The defect is that either 'equivalent' needs to be more precisely defined or the conditions for equality in 24.5.3.5 [istreambuf.iterator::equal] are incorrect. (Or both).
Consider the following example:
#include <iostream>
#include <fstream>
#include <iterator>
using namespace std;
int main() {
ifstream file1("file1.txt"), file2("file2.txt");
istreambuf_iterator<char> f1(file1), f2(file2);
cout << "f1 == f2 : " << boolalpha << (f1 == f2) << endl;
cout << "f1 = " << *f1 << endl;
cout << "f2 = " << *f2 << endl;
return 0;
}
Now assuming that neither f1 or f2 are at the end-of-stream then f1 == f2 by 24.5.3.5 [istreambuf.iterator::equal].
However, it is unlikely that *f1 will give the same value as *f2 except by accident.
So what does *f1 'equivalent' to *f2 mean? I think the standard should be clearer on this point, or at least be explicit that this does not mean that *f1 and *f2 are required to have the same value in the case of input iterators.
Proposed resolution:
Rationale:
The two iterators aer not in the domain of ==
Section: 22.2.1.4.2 [locale.codecvt.virtuals] Status: NAD Editorial Submitter: Alberto Barbati Date: 2002-12-24
View all other issues in [locale.codecvt.virtuals].
View all issues with NAD Editorial status.
Discussion:
this DR follows the discussion on the previous thread "codecvt::do_in not consuming external characters". It's just a clarification issue and not a request for a change.
Can do_in()/do_out() produce output characters without consuming input characters as a result of operation on state?
Proposed resolution:
Add a note at the end of 22.2.1.4.2 [locale.codecvt.virtuals], paragraph 3:
[Note: As a result of operations on state, it can return ok or partial and set from_next == from and to_next != to. --end note]
Rationale:
The submitter believes that standard already provides an affirmative answer to the question. However, the current wording has induced a few library implementors to make the incorrect assumption that do_in()/do_out() always consume at least one internal character when they succeed.
The submitter also believes that the proposed resolution is not in conflict with the related issue 76. Moreover, by explicitly allowing operations on state to produce characters, a codecvt implementation may effectively implement N-to-M translations without violating the "one character at a time" principle described in such issue. On a side note, the footnote in the proposed resolution of issue 76 that informally rules out N-to-M translations for basic_filebuf should be removed if this issue is accepted as valid.
[ Kona (2007): The proposed resolution is to add a note. Since this is non-normative, the issue is editorial, but we believe that the note is correct. Proposed Disposition: NAD, Editorial ]
Section: 27.6.1.3 [istream.unformatted] Status: NAD Submitter: Martin Sebor Date: 2003-01-05
View all other issues in [istream.unformatted].
View all issues with NAD status.
Discussion:
The Effects clauses for the two functions below violate the general requirements on unformatted input functions outlined in 27.6.1.3: they do not begin by constructing a sentry object. Instead, they begin by calling widen ('\n'), which may throw an exception. The exception is then allowed to propagate from the unformatted input function irrespective of the setting of exceptions().
Note that in light of 27.6.1.1, p3 and p4, the fact that the functions allow exceptions thrown from widen() to propagate may not strictly speaking be a defect (but the fact that the functions do not start by constructing a sentry object still is). However, since an exception thrown from ctype<charT> ::widen() during any other input operation (say, from within a call to num_get<charT>::get()) will be caught and cause badbit to be set, these two functions should not be treated differently for the sake of consistency.
Proposed resolution:
Rationale:
Not a defect. The standard is consistent, and the behavior required by the standard is unambiguous. Yes, it's theoretically possible for widen to throw. (Not that this will happen for the default ctype facet or for most real-world replacement ctype facets.) Users who define ctype facets that can throw, and who care about this behavior, can use alternative signatures that don't call widen.
Section: 17.3.1.1 [structure.summary] Status: Pending NAD Editorial Submitter: Martin Sebor Date: 2003-09-18
View all issues with Pending NAD Editorial status.
Discussion:
The text in 17.3.1.1, p1 says:
"Paragraphs labelled "Note(s):" or "Example(s):" are informative, other
paragraphs are normative."
The library section makes heavy use of paragraphs labeled "Notes(s),"
some of which are clearly intended to be normative (see list 1), while
some others are not (see list 2). There are also those where the intent
is not so clear (see list 3).
List 1 -- Examples of (presumably) normative Notes:
20.7.5.1 [allocator.members], p3,
20.7.5.1 [allocator.members], p10,
21.3.2 [string.cons], p11,
22.1.1.2 [locale.cons], p11,
23.2.2.3 [deque.modifiers], p2,
25.3.7 [alg.min.max], p3,
26.3.6 [complex.ops], p15,
27.5.2.4.3 [streambuf.virt.get], p7.
List 2 -- Examples of (presumably) informative Notes:
18.5.1.3 [new.delete.placement], p3,
21.3.6.6 [string::replace], p14,
22.2.1.4.2 [locale.codecvt.virtuals], p3,
25.1.4 [alg.foreach], p4,
26.3.5 [complex.member.ops], p1,
27.4.2.5 [ios.base.storage], p6.
List 3 -- Examples of Notes that are not clearly either normative
or informative:
22.1.1.2 [locale.cons], p8,
22.1.1.5 [locale.statics], p6,
27.5.2.4.5 [streambuf.virt.put], p4.
None of these lists is meant to be exhaustive.
[Definitely a real problem. The big problem is there's material that doesn't quite fit any of the named paragraph categories (e.g. Effects). Either we need a new kind of named paragraph, or we need to put more material in unnamed paragraphs jsut after the signature. We need to talk to the Project Editor about how to do this. ]
[ Bellevue: Specifics of list 3: First 2 items correct in std (22.1.1.2, 22.1.1.5) Third item should be non-normative (27.5.2.4.5), which Pete will handle editorially. ]
Proposed resolution:
[Pete: I changed the paragraphs marked "Note" and "Notes" to use "Remark" and "Remarks". Fixed as editorial. This change has been in the WD since the post-Redmond mailing, in 2004. Recommend NAD.]
[ Batavia: We feel that the references in List 2 above should be changed from Remarks to Notes. We also feel that those items in List 3 need to be double checked for the same change. Alan and Pete to review. ]
Section: 27.4.4.3 [iostate.flags] Status: Dup Submitter: Martin Sebor Date: 2003-09-18
View all other issues in [iostate.flags].
View all issues with Dup status.
Duplicate of: 412
Discussion:
The Effects clause in 27.4.4.3, p5 describing the effects of a call to the ios_base member function clear(iostate state) says that the function only throws if the respective bits are already set prior to the function call. That's obviously not the intent. If it was, a call to clear(badbit) on an object for which (rdstate() == goodbit && exceptions() == badbit) holds would not result in an exception being thrown.
Proposed resolution:
The text ought to be changed from
"If (rdstate() & exceptions()) == 0, returns. ..."
to
"If (state & exceptions()) == 0, returns. ..."
Rationale:
Section: 18.7.2.4 [unexpected] Status: NAD Submitter: Vyatcheslav Sysoltsev Date: 2003-09-29
View all issues with NAD status.
Discussion:
Clause 15.5.2 [except.unexpected] paragraph 1 says that "void unexpected(); is called (18.7.2) immediately after completing the stack unwinding for the former function", but 18.7.2.4 (Effects) says that "void unexpected(); . . . Calls the unexpected_handler function in effect immediately after evaluating the throwexpression (18.7.2.2),". Isn't here a contradiction: 15.5.2 requires stack have been unwound when in void unexpected() and therefore in unexpected_handler but 18.7.2.4 claims that unexpected_handler is called "in effect immediately" after evaluation of throw expression is finished, so there is no space left for stack to be unwound therefore? I think the phrase "in effect immediately" should be removed from the standard because it brings ambiguity in understanding.
Proposed resolution:
Rationale:
There is no contradiction. The phrase "in effect immediately" is just to clarify which handler is to be called.
Section: 27.6.2.6.2 [ostream.inserters.arithmetic] Status: NAD Submitter: Ivan Godard Date: 2003-10-24
View all other issues in [ostream.inserters.arithmetic].
View all issues with NAD status.
Discussion:
Given:
void f(int) {}
void(*g)(int) = f;
cout << g;
(with the expected #include and usings), the value printed is a rather surprising "true". Rather useless too.
The standard defines:
ostream& operator<<(ostream&, void*);
which picks up all data pointers and prints their hex value, but does not pick up function pointers because there is no default conversion from function pointer to void*. Absent that, we fall back to legacy conversions from C and the function pointer is converted to bool.
There should be an analogous inserter that prints the address of a function pointer.
Proposed resolution:
Rationale:
This is indeed a wart, but there is no good way to solve it. C doesn't provide a portable way of outputting the address of a function point either.
Section: 22.2 [locale.categories] Status: NAD Submitter: Matt Austern Date: 2003-11-02
View other active issues in [locale.categories].
View all other issues in [locale.categories].
View all issues with NAD status.
Discussion:
The following facets classes have no copy constructors described in the standard, which, according to the standard, means that they are supposed to use the compiler-generated defaults. Default copy behavior is probably inappropriate. We should either make these classes uncopyable or else specify exactly what their constructors do.
Related issue: 421.
ctype_base
ctype
ctype_byname
ctype<char>
ctype_byname<char>
codecvt_base
codecvt
codecvt_byname
num_get
num_put
numpunct
numpunct_byname
collate
collate_byname
time_base
time_get
time_get_byname
time_put
time_put_byname
money_get
money_put
money_base
moneypunct
moneypunct_byname
messages_base
messages
messages_byname
Proposed resolution:
Rationale:
The copy constructor in the base class is private.
Section: 26.3.8 [complex.transcendentals] Status: NAD Submitter: Matt Austern Date: 2003-11-05
View all issues with NAD status.
Discussion:
Operations like pow and exp on complex<T> are typically implemented in terms of operations like sin and cos on T. Should implementations write this as std::sin, or as plain unqualified sin?
The issue, of course, is whether we want to use argument-dependent lookup in the case where T is a user-defined type. This is similar to the issue of valarray transcendentals, as discussed in issue 226.
This issue differs from valarray transcendentals in two important ways. First, "the effect of instantiating the template complex for types other than float, double or long double is unspecified." (26.3.1 [complex.synopsis]) Second, the standard does not dictate implementation, so there is no guarantee that a particular real math function is used in the implementation of a particular complex function.
Proposed resolution:
Rationale:
If you instantiate std::complex for user-defined types, all bets are off.
Section: 22.1.1.1.1 [locale.category] Status: Dup Submitter: Pete Becker Date: 2003-12-26
View all other issues in [locale.category].
View all issues with Dup status.
Duplicate of: 327
Discussion:
22.1.1.1.1/4, table 52, "Required Instantiations", lists, among others:
time_get<char,InputIterator>
time_get_byname<char,InputIterator>
time_get<wchar_t,OutputIterator>
time_get_byname<wchar_t,OutputIterator>
The second argument to the last two should be InputIterator, not OutputIterator.
Proposed resolution:
Change the second template argument to InputIterator.
Rationale:
Section: 23.3.3 [set] Status: Dup Submitter: Bill Plauger Date: 2004-01-30
View all other issues in [set].
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Duplicate of: 214
Discussion:
map/multimap have:
iterator find(const key_type& x) const; const_iterator find(const key_type& x) const;
which is consistent with the table of associative container requirements. But set/multiset have:
iterator find(const key_type&) const;
set/multiset should look like map/multimap, and honor the requirements table, in this regard.
Proposed resolution:
Rationale:
Section: 23.1.4 [associative.reqmts], 23.3 [associative] Status: Dup Submitter: Bill Plauger Date: 2004-01-30
View all other issues in [associative.reqmts].
View all issues with Dup status.
Duplicate of: 130
Discussion:
map/multimap/set/multiset have:
void erase(iterator); void erase(iterator, iterator);
But there's no good reason why these can't return an iterator, as for vector/deque/list:
iterator erase(iterator); iterator erase(iterator, iterator);
Proposed resolution:
Informally: The table of associative container requirements, and the relevant template classes, should return an iterator designating the first element beyond the erased subrange.
Rationale:
Section: 22.1.1.3 [locale.members] Status: NAD Submitter: Bill Plauger Date: 2004-01-30
View all other issues in [locale.members].
View all issues with NAD status.
Discussion:
template<class Facet> locale::combine(const locale&) const;
is obliged to create a locale that has no name. This is overspecification and overkill. The resulting locale should follow the usual rules -- it has a name if the locale argument has a name and Facet is one of the standard facets.
[ Sydney and post-Sydney (see c++std-lib-13439, c++std-lib-13440, c++std-lib-13443): agreed that it's overkill to say that the locale is obligated to be nameless. However, we also can't require it to have a name. At the moment, locale names are based on categories and not on individual facets. If a locale contains two different facets of different names from the same category, then this would not fit into existing naming schemes. We need to give implementations more freedom. Bill will provide wording. ]
Rationale:
After further discussion the LWG decided to close this as NAD. The fundamental problem is that names right now are per-category, not per-facet. The combine member function works at the wrong level of granularity.
Section: 3.6.3 [basic.start.term], 18.3 [cstdint] Status: NAD Submitter: Bill Plauger Date: 2004-03-23
View all issues with NAD status.
Discussion:
3.6.3 Termination spells out in detail the interleaving of static destructor calls and calls to functions registered with atexit. To match this behavior requires intimate cooperation between the code that calls destructors and the exit/atexit machinery. The former is tied tightly to the compiler; the latter is a primitive mechanism inherited from C that traditionally has nothing to do with static construction and destruction. The benefits of intermixing destructor calls with atexit handler calls is questionable at best, and very difficult to get right, particularly when mixing third-party C++ libraries with different third-party C++ compilers and C libraries supplied by still other parties.
I believe the right thing to do is defer all static destruction until after all atexit handlers are called. This is a change in behavior, but one that is likely visible only to perverse test suites. At the very least, we should permit deferred destruction even if we don't require it.
[If this is to be changed, it should probably be changed by CWG. At this point, however, the LWG is leaning toward NAD. Implementing what the standard says is hard work, but it's not impossible and most vendors went through that pain years ago. Changing this behavior would be a user-visible change, and would break at least one real application.]
[ Batavia: Send to core with our recommendation that we should permit deferred destruction but not require it. ]
[ Howard: The course of action recommended in Batavia would undo LWG issue 3 and break current code implementing the "phoenix singleton". Search the net for "phoenix singleton atexit" to get a feel for the size of the adverse impact this change would have. Below is sample code which implements the phoenix singleton and would break if atexit is changed in this way: ]
#include <cstdlib>
#include <iostream>
#include <type_traits>
#include <new>
class A
{
bool alive_;
A(const A&);
A& operator=(const A&);
public:
A() : alive_(true) {std::cout << "A()\n";}
~A() {alive_ = false; std::cout << "~A()\n";}
void use()
{
if (alive_)
std::cout << "A is alive\n";
else
std::cout << "A is dead\n";
}
};
void deallocate_resource();
// This is the phoenix singleton pattern
A& get_resource(bool create = true)
{
static std::aligned_storage<sizeof(A), std::alignment_of<A>::value>::type buf;
static A* a;
if (create)
{
if (a != (A*)&buf)
{
a = ::new (&buf) A;
std::atexit(deallocate_resource);
}
}
else
{
a->~A();
a = (A*)&buf + 1;
}
return *a;
}
void deallocate_resource()
{
get_resource(false);
}
void use_A(const char* message)
{
A& a = get_resource();
std::cout << "Using A " << message << "\n";
a.use();
}
struct B
{
~B() {use_A("from ~B()");}
};
B b;
int main()
{
use_A("from main()");
}
The correct output is:
A() Using A from main() A is alive ~A() A() Using A from ~B() A is alive ~A()
[ Bellevue: Confirmed no interaction with quick_exit. Strong feeling against mandating the change. Leaning towards NAD rather than permitting the change, as this would make common implementations of pheonix-singleton pattern implementation defined, as noted by Howard. Bill agrees issue is no longer serious, and accepts NAD. ]
Proposed resolution:
Section: 21.3.1 [string.require] Status: NAD Submitter: Daniel Frey Date: 2004-06-10
View all other issues in [string.require].
View all issues with NAD status.
Discussion:
Today, my colleagues and me wasted a lot of time. After some time, I found the problem. It could be reduced to the following short example:
#include <string>
int main() { std::string( 0 ); }
The problem is that the tested compilers (GCC 2.95.2, GCC 3.3.1 and Comeau online) compile the above without errors or warnings! The programs (at least for the GCC) resulted in a SEGV.
I know that the standard explicitly states that the ctor of string requires a char* which is not zero. STLs could easily detect the above case with a private ctor for basic_string which takes a single 'int' argument. This would catch the above code at compile time and would not ambiguate any other legal ctors.
[Redmond: No great enthusiasm for doing this. If we do, however, we want to do it for all places that take charT* pointers, not just the single-argument constructor. The other question is whether we want to catch this at compile time (in which case we catch the error of a literal 0, but not an expression whose value is a null pointer), at run time, or both.]
Proposed resolution:
Rationale:
Recommend NAD. Relegate this functionality to debugging implementations.
Section: 23 [containers] Status: NAD Submitter: Martin Sebor Date: 2004-06-28
View other active issues in [containers].
View all other issues in [containers].
View all issues with NAD status.
Discussion:
The standard doesn't prohibit the destructors (or any other special functions) of containers' elements invoked from a member function of the container from "recursively" calling the same (or any other) member function on the same container object, potentially while the container is in an intermediate state, or even changing the state of the container object while it is being modified. This may result in some surprising (i.e., undefined) behavior.
Read email thread starting with c++std-lib-13637 for more.
Proposed resolution:
Add to Container Requirements the following new paragraph:
Unless otherwise specified, the behavior of a program that
invokes a container member function f from a member function
g of the container's value_type on a container object c that
called g from its mutating member function h, is undefined.
I.e., if v is an element of c, directly or indirectly calling
c.h() from v.g() called from c.f(), is undefined.
[Redmond: This is a real issue, but it's probably a clause 17 issue, not clause 23. We get the same issue, for example, if we try to destroy a stream from one of the stream's callback functions.]
Rationale:
Recommend NAD. We agree this is an issue, but not a defect. We believe that there is no wording we can put in the standard that will cover all cases without introducing unfortunate corner cases.
Section: 25.3.3.3 [equal.range] Status: Dup Submitter: Prateek R Karandikar Date: 2004-06-30
View all other issues in [equal.range].
View all issues with Dup status.
Duplicate of: 270
Discussion:
There is no "Returns:" clause for std::equal_range, which returns non-void.
Proposed resolution:
Rationale:
Fixed as part of issue 270.
Section: 24.1.3 [forward.iterators] Status: NAD Submitter: Dave Abrahams Date: 2004-07-09
View all other issues in [forward.iterators].
View all issues with NAD status.
Discussion:
24.1/3 says:
Forward iterators satisfy all the requirements of the input and output iterators and can be used whenever either kind is specified
The problem is that satisfying the requirements of output iterator means that you can always assign *something* into the result of dereferencing it. That makes almost all non-mutable forward iterators non-conforming. I think we need to sever the refinement relationship between forward iterator and output iterator.
Related issue: 200. But this is not a dup.
Proposed resolution:
Rationale:
Yes, 24.1/3 does say that. But it's introductory material. The precise specification is in 24.1.3, and the requrements table there is right. We don't need to fine-tune introductory wording. (Especially since this wording is likely to be changed as part of the iterator overhaul.)
Section: 24.1.3 [forward.iterators] Status: Dup Submitter: Dave Abrahams Date: 2004-07-11
View all other issues in [forward.iterators].
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Duplicate of: 478
Discussion:
The Forward Iterator requirements table contains the following:
expression return type operational precondition
semantics
========== ================== =========== ==========================
a->m U& if X is mutable, (*a).m pre: (*a).m is well-defined.
otherwise const U&
r->m U& (*r).m pre: (*r).m is well-defined.
The first line is exactly right. The second line is wrong. Basically it implies that the const-ness of the iterator affects the const-ness of referenced members. But Paragraph 11 of [lib.iterator.requirements] says:
In the following sections, a and b denote values of type const X, n denotes a value of the difference type Distance, u, tmp, and m denote identifiers, r denotes a value of X&, t denotes a value of value type T, o denotes a value of some type that is writable to the output iterator.
AFAICT if we need the second line at all, it should read the same as the first line.
Related issue: 478
Proposed resolution:
Rationale:
The LWG agrees that this is a real problem. Marked as a DUP because the LWG chose to adopt the solution proposed in 478.
Section: 23.1 [container.requirements] Status: Dup Submitter: Herb Sutter Date: 2004-08-01
View other active issues in [container.requirements].
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Duplicate of: 580
Discussion:
Nothing in the standard appears to make this program ill-formed:
struct C {
void* operator new( size_t s ) { return ::operator new( s ); }
// NOTE: this hides in-place and nothrow new
};
int main() {
vector<C> v;
v.push_back( C() );
}
Is that intentional? We should clarify whether or not we intended to require containers to support types that define their own special versions of operator new.
[ Lillehammer: A container will definitely never use this overridden operator new, but whether it will fail to compile is unclear from the standard. Are containers supposed to use qualified or unqualified placement new? 20.4.1.1 is somewhat relevant, but the standard doesn't make it completely clear whether containers have to use Allocator::construct(). If containers don't use it, the details of how containers use placement new are unspecified. That is the real bug, but it needs to be fixed as part of the allocator overhaul. Weak support that the eventual solution should make this code well formed. ]
Proposed resolution:
Section: 20.6.3 [base] Status: NAD Submitter: Joe Gottman Date: 2004-08-19
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Discussion:
The classes std::unary_function and std::binary_function are both designed to be inherited from but contain no virtual functions. This makes it too easy for a novice programmer to write code like binary_function<int, int, int> *p = new plus<int>; delete p;
There are two common ways to prevent this source of undefined behavior: give the base class a public virtual destructor, or give it a protected nonvirtual destructor. Since unary_function and binary_function have no other virtual functions, (note in particular the absence of an operator()() ), it would cost too much to give them public virtual destructors. Therefore, they should be given protected nonvirtual destructors.
Proposed resolution:
Change Paragraph 20.3.1 of the Standard from
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
};
template <class Arg1, class Arg2, class Result>
struct binary_function {
typedef Arg1 first_argument_type;
typedef Arg2 second_argument_type;
typedef Result result_type;
};
to
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
protected:
~unary_function() {}
};
template <class Arg1, class Arg2, class Result>
struct binary_function {
typedef Arg1 first_argument_type;
typedef Arg2 second_argument_type;
typedef Result result_type;
protected:
~binary_function() {}
};
Rationale:
The LWG doesn't believe the existing definition causes anybody any concrete harm.
Section: 25.2.9 [alg.unique] Status: NAD Submitter: Andrew Koenig Date: 2004-08-30
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Discussion:
The standard says that unique(first, last) "eliminates all but the first element from every consecutive group of equal elements" in [first, last) and returns "the end of the resulting range". So a postcondition is that [first, result) is the same as the old [first, last) except that duplicates have been eliminated.
What postconditions are there on the range [result, last)? One might argue that the standard says nothing about those values, so they can be anything. One might also argue that the standard doesn't permit those values to be changed, so they must not be. Should the standard say something explicit one way or the other?
Proposed resolution:
Rationale:
We don't want to make many guarantees about what's in [result, end). Maybe we aren't being quite explicit enough about not being explicit, but it's hard to think that's a major problem.
Section: 20.2.3 [pairs], 20.4 [tuple] Status: NAD Editorial Submitter: Andrew Koenig Date: 2004-09-14
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Discussion:
(Based on recent comp.std.c++ discussion)
Pair (and tuple) should specialize std::swap to work in terms of std::swap on their components. For example, there's no obvious reason why swapping two objects of type pair<vector<int>, list<double> > should not take O(1).
[Lillehammer: We agree it should be swappable. Howard will provide wording.]
[ Post Oxford: We got swap for pair but accidently missed tuple. tuple::swap is being tracked by 522. ]
Proposed resolution:
Wording provided in N1856.
Rationale:
Recommend NAD, fixed by N1856.
Section: 25.1 [alg.nonmodifying], 25.2 [alg.modifying.operations] Status: Dup Submitter: Peter Dimov Date: 2004-09-20
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Duplicate of: 283
Discussion:
c++std-lib-14262
[lib.alg.find] requires T to be EqualityComparable:
template <class InputIterator, class T>
InputIterator find(InputIterator first, InputIterator last,
const T& value);
However the condition being tested, as specified in the Effects clause, is actually *i == value, where i is an InputIterator.
The two clauses are in agreement only if the type of *i is T, but this isn't necessarily the case. *i may have a heterogeneous comparison operator that takes a T, or a T may be convertible to the type of *i.
Further discussion (c++std-lib-14264): this problem affects a number of algorithsm in clause 25, not just find. We should try to resolve this problem everywhere it appears.
Proposed resolution:
[lib.alg.find]:
Remove [lib.alg.find]/1.
[lib.alg.count]:
Remove [lib.alg.count]/1.
[lib.alg.search]:
Remove "Type T is EqualityComparable (20.1.1), " from [lib.alg.search]/4.
[lib.alg.replace]:
Remove [lib.alg.replace]/1. Replace [lb.alg.replace]/2 with:
For every iterator i in the range [first, last) for which *i == value or pred(*i) holds perform *i = new_value.
Remove the first sentence of /4. Replace the beginning of /5 with:
For every iterator i in the range [result, result + (last - first)), assign to *i either...
(Note the defect here, current text says assign to i, not *i).
[lib.alg.fill]:
Remove "Type T is Assignable (23.1), " from /1. Replace /2 with:
For every iterator i in the range [first, last) or [first, first + n), perform *i = value.
[lib.alg.remove]:
Remove /1. Remove the first sentence of /6.
Rationale:
Duplicate of (a subset of) issue 283.
Section: 25.3.7 [alg.min.max] Status: Dup Submitter: Dave Abrahams Date: 2004-10-13
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Duplicate of: 281
Discussion:
A straightforward implementation of these algorithms does not need to copy T.
Proposed resolution:
drop the the words "and CopyConstructible" from paragraphs 1 and 4
Rationale:
Section: 20.1.2 [allocator.requirements] Status: NAD Submitter: Dhruv Matani Date: 2004-10-17
View other active issues in [allocator.requirements].
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Discussion:
The standard's version of allocator::construct(pointer, const_reference) severely limits what you can construct using this function. Say you can construct a socket from a file descriptor. Now, using this syntax, I first have to manually construct a socket from the fd, and then pass the constructed socket to the construct() function so it will just to an uninitialized copy of the socket I manually constructed. Now it may not always be possible to copy construct a socket eh! So, I feel that the changes should go in the allocator::construct(), making it:
template<typename T>
struct allocator{
template<typename T1>
void construct(pointer T1 const& rt1);
};
Now, the ctor of the class T which matches the one that takes a T1 can be called! Doesn't that sound great?
Proposed resolution:
Rationale:
NAD. STL uses copying all the time, and making it possible for allocators to construct noncopyable objects is useless in the absence of corresponding container changes. We might consider this as part of a larger redesign of STL.
Section: 25.2.8 [alg.remove] Status: NAD Submitter: Thomas Mang Date: 2004-12-12
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Discussion:
In Section 25.2.7 [lib.alg.remove], paragraphs 1 to 5 describe the behavior of the mutating sequence operations std::remove and std::remove_if. However, the wording does not reflect the intended behavior [Note: See definition of intended behavior below] of these algorithms, as it is known to the C++ community [1].
1) Analysis of current wording:
25.2.7 [lib.alg.remove], paragraph 2:
Current wording says: "Effects: Eliminates all the elements referred to by iterator i in the range [first, last) for which the following corresponding conditions hold: *i == value, pred(*i) != false."
This sentences expresses specifically that all elements denoted by the (original) range [first, last) for which the corresponding condition hold will be eliminated. Since there is no formal definition of the term "eliminate" provided, the meaning of "eliminate" in everyday language implies that as postcondition, no element in the range denoted by [first, last) will hold the corresponding condition on reiteration over the range [first, last).
However, this is neither the intent [Note: See definition of intended behavior below] nor a general possible approach. It can be easily proven that if all elements of the original range[first, last) will hold the condition, it is not possible to substitute them by an element for which the condition will not hold.
25.2.7 [lib.alg.remove], paragraph 3:
Current wording says: "Returns: The end of the resulting range."
The resulting range is not specified. In combination with 25.2.7 [lib.alg.remove], paragraph 2, the only reasonable interpretation of this so-called resulting range is the range [first,last) - thus returning always the ForwardIterator 'last' parameter.
25.2.7 [lib.alg.remove], paragraph 4:
Current wording says: "Notes: Stable: the relative order of the elements that are not removed is the same as their relative order in the original range"
This sentences makes use of the term "removed", which is neither specified, nor used in a previous paragraph (which uses the term "eliminate"), nor unamgiuously separated from the name of the algorithm.
2) Description of intended behavior:
For the rest of this Defect Report, it is assumed that the intended behavior was that all elements of the range [first, last) which do not hold the condition *i == value (std::remove) or pred(*i) != false (std::remove_if)], call them s-elements [Note: s...stay], will be placed into a contiguous subrange of [first, last), denoted by the iterators [first, return value). The number of elements in the resulting range [first, return value) shall be equal to the number of s-elements in the original range [first, last). The relative order of the elements in the resulting subrange[first, return value) shall be the same as the relative order of the corresponding elements in the original range. It is undefined whether any elements in the resulting subrange [return value, last) will hold the corresponding condition, or not.
All implementations known to the author of this Defect Report comply with this intent. Since the intent of the behavior (contrary to the current wording) is also described in various utility references serving the C++ community [1], it is not expected that fixing the paragraphs will influence current code - unless the code relies on the behavior as it is described by current wording and the implementation indeed reflects the current wording, and not the intent.
3) Proposed fixes:
Change 25.2.7 [lib.alg.remove], paragraph 2 to:
"Effect: Places all the elements referred to by iterator i in the range [first, last) for which the following corresponding conditions hold : !(*i == value), pred(*i) == false into the subrange [first, k) of the original range, where k shall denote a value of type ForwardIterator. It is undefined whether any elements in the resulting subrange [k, last) will hold the corresponding condition, or not."
Comments to the new wording:
a) "Places" has no special meaning, and the everyday language meaning should fit. b) The corresponding conditions were negated compared to the current wording, becaue the new wording requires it. c) The wording "of the original range" might be redundant, since any subrange starting at 'first' and containing no more elements than the original range is implicitly a subrange of the original range [first, last). d) The iterator k was introduced instead of "return value" in order to avoid a cyclic dependency on 25.2.7/3. The wording ", where k shall denote a value of type ForwardIterator" might be redundant, because it follows implicitly by 25.2.7/3. e) "Places" does, in the author's opinion, explicitly forbid duplicating any element holding the corresponding condition in the original range [first, last) within the resulting range [first, k). If there is doubt this term might be not unambiguous regarding this, it is suggested that k is specified more closely by the following wording: "k shall denote a value of type ForwardIterator [Note: see d)] so that k - first is equal to the number of elements in the original range [first, last) for which the corresponding condition did hold". This could also be expressed as a separate paragraph "Postcondition:" f) The senctence "It is undefined whether any elements in the resulting subrange [k, last) will hold the corresponding condition, or not." was added consciously so the term "Places" does not imply if the original range [first, last) contains n elements holding the corresponding condition, the identical range[first, last) will also contain exactly n elements holding the corresponding condition after application of the algorithm.
Change 25.2.7 [lib.alg.remove], paragraph 3 to: "Returns: The iterator k."
Change 25.2.7 [lib.alg.remove], paragraph 4 to: "Notes: Stable: the relative order of the elements that are placed into the subrange [first, return value) shall be the same as their relative order was in the original range [first, last) prior to application of the algorithm."
Comments to the new wording:
a) the wording "was ... prior to application of the algorithm" is used to explicitly distinguish the original range not only by means of iterators, but also by a 'chronological' factor from the resulting range [first, return value). It might be redundant.
[1]: The wording of these references is not always unambiguous, and provided examples partially contradict verbal description of the algorithms, because the verbal description resembles the problematic wording of ISO/IEC 14882:2003.
Proposed resolution:
Rationale:
The LWG believes that the standard is sufficiently clear, and that there is no evidence of any real-world confusion about this point.
Section: 25.2.9 [alg.unique] Status: NAD Submitter: Thomas Mang Date: 2004-12-12
View all other issues in [alg.unique].
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Discussion:
In Section 25.2.8 [lib.alg.unique], paragraphs 1 to 3 describe the behavior of the mutating sequence operation std::unique. However, the wording does not reflect the intended behavior [Note: See definition of intended behavior below] of these algorithms, as it is known to the C++ community [1].
1) Analysis of current wording:
25.2.8 [lib.alg.unique], paragraph 1:
Current wording says: "Effects: Eliminates all but the first element from every consecutive group of equal elements referred to by the iterator i in the range [first, last) for which the following corresponding conditions hold: *i == *(i - 1) or pred(*i, *(i -1)) != false"
This sentences expresses specifically that all elements denoted by the (original) range [first, last) which are not but the first element from a consecutive group of equal elements (where equality is defined as *i == *(i - 1) or pred(*i, *(i - 1)) ! = false) [Note: See DR 202], call them r-elements [Note: r...remove], will be eliminated. Since there is no formal definition of the term "eliminate" provided, it is undefined how this "elimination" takes place. But the meaning of "eliminate" in everyday language seems to disallow explicitly that after application of the algorithm, any r-element will remain at any position of the range [first, last) [2].
Another defect in the current wording concerns the iterators used to compare two elements for equality: The current wording contains the expression "(i - 1)", which is not covered by 25/9 [Note: See DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions].
25.2.8 [lib.alg.unique], paragraph 2:
Current wording says: "Returns: The end of the resulting range."
The resulting range is not specified. In combination with 25.2.8 [lib.alg.unique], paragraph 1, one reasonable interpretation (in the author's opinion even the only possible interpretation) of this so-called resulting range is the range [first, last) - thus returning always the ForwardIterator 'last' parameter.
2) Description of intended behavior:
For the rest of this Defect Report, it is assumed that the intended behavior was that all elements denoted by the original range [first, last) which are the first element from a consecutive group of elements for which the corresponding conditions: *(i-1) == *i (for the version of unique without a predicate argument) or pred(*(i-1), *i) ! = false (for the version of unique with a predicate argument) [Note: If such a group of elements consists of only a single element, this is also considered the first element] [Note: See resolutions of DR 202], call them s-elements [Note: s...stay], will be placed into a contiguous subrange of [first, last), denoted by the iterators [first, return value). The number of elements in the resulting range [first, return value) shall be equal to the number of s-elements in the original range [first, last). Invalid iterator arithmetic expressions are expected to be resolved as proposed in DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions. It is also assumed by the author that the relative order of the elements in the resulting subrange [first, return value) shall be the same as the relative order of the corresponding elements (the s-elements) in the original range [Note: If this was not intended behavior, the additional proposed paragraph about stable order will certainly become obsolete]. Furthermore, the resolutions of DR 202 are partially considered.
All implementations known to the author of this Defect Report comply with this intent [Note: Except possible effects of DR 202]. Since this intent of the behavior (contrary to the current wording) is also described in various utility references serving the C++ community [1], it is not expected that fixing the paragraphs will influence current code [Note: Except possible effects of DR 202] - unless the code relies on the behavior as it is described by current wording and the implementation indeed reflects the current wording, and not the intent.
3) Proposed fixes:
Change 25.2.8 [lib.alg.unique], paragraph 1 to:
"Effect: Places the first element from every consecutive group of elements, referred to by the iterator i in the range [first, last), for which the following conditions hold: *(i-1) == *i (for the version of unique without a predicate argument) or pred(*(i -1), *i) != false (for the version of unique with a predicate argument), into the subrange [first, k) of the original range, where k shall denote a value of type ForwardIterator."
Comments to the new wording:
a) The new wording was influenced by the resolutions of DR 202. If DR 202 is resolved in another way, the proposed wording need also additional review. b) "Places" has no special meaning, and the everyday language meaning should fit. c) The expression "(i - 1)" was left, but is expected that DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions will take this into account. d) The wording "(for the version of unique without a predicate argument)" and "(for the version of unique with a predicate argument)" was added consciously for clarity and is in resemblence with current 23.2.2.4 [lib.list.ops], paragraph 19. It might be considered redundant. e) The wording "of the original range" might be redundant, since any subrange starting at first and containing no more elements than the original range is implicitly a subrange of the original range [first, last). f) The iterator k was introduced instead of "return value" in order to avoid a cyclic dependency on 25.2.8 [lib.alg.unique], paragraph 2. The wording ", where k shall denote a value of type ForwardIterator" might be redundant, because it follows implicitly by 25.2.8 [lib.alg.unique], paragraph 2. g) "Places" does, in the author's opinion, explicitly forbid duplicating any s-element in the original range [first, last) within the resulting range [first, k). If there is doubt this term might be not unambiguous regarding this, it is suggested that k is specified more closely by the following wording: "k shall denote a value of type ForwardIterator [Note: See f)] so that k - first is equal to the number of elements in the original range [first, last) being the first element from every consecutive group of elements for which the corresponding condition did hold". This could also be expressed as a separate paragraph "Postcondition:". h) If it is considered that the wording is unclear whether it declares the element of a group which consists of only a single element implicitly to be the first element of this group [Note: Such an interpretation could eventually arise especially in case last - first == 1] , the following additional sentence is proposed: "If such a group of elements consists of only a single element, this element is also considered the first element."
Change 25.2.8 [lib.alg.unique], paragraph 2 to: "Returns: The iterator k."
Add a separate paragraph "Notes:" as 25.2.8 [lib.alg.unique], paragraph 2a or 3a, or a separate paragraph "Postcondition:" before 25.2.8 [lib.alg.unique], paragraph 2 (wording inside {} shall be eliminated if the preceding expressions are used, or the preceding expressions shall be eliminated if wording inside {} is used):
"Notes:{Postcondition:} Stable: the relative order of the elements that are placed into the subrange [first, return value {k}) shall be the same as their relative order was in the original range [first, last) prior to application of the algorithm."
Comments to the new wording:
a) It is assumed by the author that the algorithm was intended to be stable. In case this was not the intent, this paragraph becomes certainly obsolete. b) The wording "was ... prior to application of the algorithm" is used to explicitly distinguish the original range not only by means of iterators, but also by a 'chronological' factor from the resulting range [first, return value). It might be redundant.
25.2.8 [lib.alg.unique], paragraph 3:
See DR 239.
4) References to other DRs:
See DR 202, but which does not address any of the problems described in this Defect Report [Note: This DR is supposed to complement DR 202]. See DR 239. See DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions.
[1]: The wording of these references is not always unambiguous, and provided examples partially contradict verbal description of the algorithms, because the verbal description resembles the problematic wording of ISO/IEC 14882:2003.
[2]: Illustration of conforming implementations according to current wording:
One way the author of this DR considers how this "elimination" could be achieved by a conforming implementation according to current wording is by substituting each r-element by _any_ s-element [Note: s...stay; any non-r-element], since all r-elements are "eliminated".
In case of a sequence consisting of elements being all 'equal' [Note: See DR 202], substituting each r-element by the single s-element is the only possible solution according to current wording.
Proposed resolution:
Rationale:
The LWG believes the standard is sufficiently clear. No implementers get it wrong, and changing it wouldn't cause any code to change, so there is no real-world harm here.
Section: 23.2.4.4 [list.ops] Status: NAD Submitter: Thomas Mang Date: 2004-12-12
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Discussion:
In Section 23.2.4.4 [list.ops], paragraphs 19 to 21 describe the behavior of the std::list<T, Allocator>::unique operation. However, the current wording is defective for various reasons.
1) Analysis of current wording:
23.2.4.4 [list.ops], paragraph 19:
Current wording says: "Effects: Eliminates all but the first element from every consecutive group of equal elements referred to by the iterator i in the range [first + 1, last) for which *i == *(i - 1) (for the version of unique with no argument) or pred(*i, *(i -1)) (for the version of unique with a predicate argument) holds."
This sentences makes use of the undefined term "Eliminates". Although it is, to a certain degree, reasonable to consider the term "eliminate" synonymous with "erase", using "Erase" in the first place, as the wording of 23.2.4.4 [list.ops], paragraph 15 does, would be clearer.
The range of the elements referred to by iterator i is "[first + 1, last)". However, neither "first" nor "last" is defined.
The sentence makes three times use of iterator arithmetic expressions ( "first + 1", "*i == *(i - 1)", "pred(*i, *(i -1))" ) which is not defined for bidirectional iterator [see DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions].
The same problems as pointed out in DR 202 (equivalence relation / order of arguments for pred()) apply to this paragraph.
23.2.4.4 [list.ops], paragraph 20:
Current wording says: "Throws: Nothing unless an exception in thrown by *i == *(i-1) or pred(*i, *(i - 1))"
The sentence makes two times use of invalid iterator arithmetic expressions ( "*i == *(i - 1)", "pred(*i, *(i -1))" ).
[Note: Minor typos: "in" / missing dot at end of sentence.]
23.2.4.4 [list.ops], paragraph 21:
Current wording says: "Complexity: If the range (last - first) is not empty, exactly (last - first) - 1 applications of the corresponding predicate, otherwise no application of the predicate.
See DR 315 regarding "(last - first)" not yielding a range.
Invalid iterator arithmetic expression "(last - first) - 1" left .
2) Description of intended behavior:
For the rest of this Defect Report, it is assumed that "eliminate" is supposed to be synonymous to "erase", that "first" is equivalent to an iterator obtained by a call to begin(), "last" is equivalent to an iterator obtained by a call to end(), and that all invalid iterator arithmetic expressions are resolved as described in DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions.
Furthermore, the resolutions of DR 202 are considered regarding equivalence relation and order of arguments for a call to pred.
All implementations known to the author of this Defect Report comply with these assumptions, apart from the impact of the alternative resolution of DR 202. Except for the changes implied by the resolutions of DR 202, no impact on current code is expected.
3) Proposed fixes:
Change 23.2.4.4 [list.ops], paragraph 19 to:
"Effect: Erases all but the first element from every consecutive group of elements, referred to by the iterator i in the range [begin(), end()), for which the following conditions hold: *(i-1) == *i (for the version of unique with no argument) or pred(*(i-1), *i) != false (for the version of unique with a predicate argument)."
Comments to the new wording:
a) The new wording was influenced by DR 202 and the resolutions presented there. If DR 202 is resolved in another way, the proposed wording need also additional review. b) "Erases" refers in the author's opinion unambiguously to the member function "erase". In case there is doubt this might not be unamgibuous, a direct reference to the member function "erase" is suggested [Note: This would also imply a change of 23.2.4.4 [list.ops], paragraph 15.]. c) The expression "(i - 1)" was left, but is expected that DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions will take this into account. d) The wording "(for the version of unique with no argument)" and "(for the version of unique with a predicate argument)" was kept consciously for clarity. e) "begin()" substitutes "first", and "end()" substitutes "last". The range need adjustment from "[first + 1, last)" to "[begin(), end())" to ensure a valid range in case of an empty list. f) If it is considered that the wording is unclear whether it declares the element of a group which consists of only a single element implicitly to be the first element of this group [Note: Such an interpretation could eventually arise especially in case size() == 1] , the following additional sentence is proposed: "If such a group of elements consists of only a single element, this element is also considered the first element."
Change 23.2.4.4 [list.ops], paragraph 20 to:
"Throws: Nothing unless an exception is thrown by *(i-1) == *i or pred(*(i-1), *i)."
Comments to the new wording:
a) The wording regarding the conditions is identical to proposed 23.2.4.4 [list.ops], paragraph 19. If 23.2.4.4 [list.ops], paragraph 19 is resolved in another way, the proposed wording need also additional review. b) The expression "(i - 1)" was left, but is expected that DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions will take this into account. c) Typos fixed.
Change 23.2.4.4 [list.ops], paragraph 21 to:
"Complexity: If empty() == false, exactly size() - 1 applications of the corresponding predicate, otherwise no applications of the corresponding predicate."
Comments to the new wording:
a) The new wording is supposed to also replace the proposed resolution of DR 315, which suffers from the problem of undefined "first" / "last".
5) References to other DRs:
See DR 202. See DR 239. See DR 315. See DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions.
Proposed resolution:
Rationale:
"All implementations known to the author of this Defect Report comply with these assumption", and "no impact on current code is expected", i.e. there is no evidence of real-world confusion or harm.
Section: 24.1.1 [input.iterators] Status: NAD Submitter: Chris Jefferson Date: 2004-12-13
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Discussion:
1) In 24.1.1/3, the following text is currently present.
"Note: For input iterators, a==b does not imply ++a=++b (Equality does not guarantee the substitution property or referential transparency)."
However, when in Table 72, part of the definition of ++r is given as:
"pre: r is dereferenceable. post: any copies of the previous value of r are no longer required either to be dereferenceable ..."
While a==b does not imply that b is a copy of a, this statement should perhaps still be made more clear.
2) There are no changes to intended behaviour
3) This Note should be altered to say "Note: For input iterators a==b, when its behaviour is defined ++a==++b may still be false (Equality does not guarantee the substitution property or referential transparency).
Proposed resolution:
Rationale:
This is descriptive text, not normative, and the meaning is clear.
Section: 23.1.4 [associative.reqmts] Status: NAD Submitter: Hans B os Date: 2004-12-19
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Discussion:
According to [lib.associative.reqmts] table 69, the runtime comlexity of insert(p, t) and erase(q) can be done in amortized constant time.
It was my understanding that an associative container could be implemented as a balanced binary tree.
For inser(p, t), you 'll have to iterate to p's next node to see if t can be placed next to p. Furthermore, the insertion usually takes place at leaf nodes. An insert next to the root node will be done at the left of the root next node
So when p is the root node you 'll have to iterate from the root to its next node, which takes O(log(size)) time in a balanced tree.
If you insert all values with insert(root, t) (where root is the root of the tree before insertion) then each insert takes O(log(size)) time. The amortized complexity per insertion will be O(log(size)) also.
For erase(q), the normal algorithm for deleting a node that has no empty left or right subtree, is to iterate to the next (or previous), which is a leaf node. Then exchange the node with the next and delete the leaf node. Furthermore according to DR 130, erase should return the next node of the node erased. Thus erasing the root node, requires iterating to the next node.
Now if you empty a map by deleting the root node until the map is empty, each operation will take O(log(size)), and the amortized complexity is still O(log(size)).
The operations can be done in amortized constant time if iterating to the next node can be done in (non amortized) constant time. This can be done by putting all nodes in a double linked list. This requires two extra links per node. To me this is a bit overkill since you can already efficiently insert or erase ranges with erase(first, last) and insert(first, last).
Proposed resolution:
Rationale:
Only "amortized constant" in special circumstances, and we believe that's implementable. That is: doing this N times will be O(N), not O(log N).
Section: 25.3.1.2 [stable.sort] Status: NAD Editorial Submitter: Prateek Karandikar Date: 2005-04-12
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Discussion:
17.3.1.1 Summary
1 The Summary provides a synopsis of the category, and introduces the first-level subclauses. Each subclause also provides a summary, listing the headers specified in the subclause and the library entities provided in each header.
2 Paragraphs labelled "Note(s):" or "Example(s):" are informative, other paragraphs are normative.
So this means that a "Notes" paragraph wouldn't be normative.
25.3.1.2 stable_sort
template<class RandomAccessIterator> void stable_sort(RandomAccessIterat or first, RandomAccessIterator last); template<class RandomAccessIterator, class Compare> void stable_sort(RandomAccessIterat or first, RandomAccessIterator last, Compare comp);1 Effects: Sorts the elements in the range [first, last).
2 Complexity: It does at most N(log N)^2 (where N == last - first) comparisons; if enough extra memory is available, it is N log N.
3 Notes: Stable: the relative order of the equivalent elements is preserved.
The Notes para is informative, and nowhere else is stability mentioned above.
Also, I just searched for the word "stable" in my copy of the Standard. and the phrase "Notes: Stable: the relative order of the elements..." is repeated several times in the Standard library clauses for describing various functions. How is it that stability is talked about in the informative paragraph? Or am I missing something obvious?
Proposed resolution:
Rationale:
This change has already been made.
Section: 22.2.1.5 [locale.codecvt.byname] Status: NAD Submitter: Krzysztof Żelechowski Date: 2005-05-24
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Discussion:
Contradiction.
Proposed resolution:
Section: 20.6.3 [base] Status: NAD Submitter: Me <anti_spam_email2003@yahoo.com> Date: 2005-06-07
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Discussion:
"For templates greater, less, greater_equal, and less_equal, the specializations for any pointer type yield a total order, even if the built-in operators <, >, <=, >= do not."
The standard should do much better than guarantee that these provide a total order, it should guarantee that it can be used to test if memory overlaps, i.e. write a portable memmove. You can imagine a platform where the built-in operators use a uint32_t comparison (this tests for overlap on this platform) but the less<T*> functor is allowed to be defined to use a int32_t comparison. On this platform, if you use std::less with the intent of making a portable memmove, comparison on an array that straddles the 0x7FFFFFFF/0x8000000 boundary can give incorrect results.
Proposed resolution:
Add a footnote to 20.5.3/8 saying:
Given a p1 and p2 such that p1 points to N objects of type T and p2 points to M objects of type T. If [p1,p1+N) does not overlap [p2,p2+M), less returns the same value when comparing all pointers in [p1,p1+N) to all pointers in [p2,p2+M). Otherwise, there is a value Q and a value R such that less returns the same value when comparing all pointers in [p1,p1+Q) to all pointers in [p2,p2+R) and an opposite value when comparing all pointers in [p1+Q,p1+N) to all pointers in [p2+R,p2+M). For the sake of completeness, the null pointer value (4.10) for T is considered to be an array of 1 object that doesn't overlap with any non-null pointer to T. less_equal, greater, greater_equal, equal_to, and not_equal_to give the expected results based on the total ordering semantics of less. For T of void, treat it as having similar semantics as T of char i.e. less<cv T*>(a, b) gives the same results as less<cv void*>(a, b) which gives the same results as less<cv char*>((cv char*)(cv void*)a, (cv char*)(cv void*)b).
I'm also thinking there should be a footnote to 20.5.3/1 saying that if A and B are similar types (4.4/4), comp<A>(a,b) returns the same value as comp<B>(a,b) (where comp is less, less_equal, etc.). But this might be problematic if there is some really funky operator overloading going on that does different things based on cv (that should be undefined behavior if somebody does that though). This at least should be guaranteed for all POD types (especially pointers) that use the built-in comparison operators.
Rationale:
less is already required to provide a strict weak ordering which is good enough to detect overlapping memory situations.
Section: 26.4.1 [rand.req], TR1 5.1.1 [tr.rand.req] Status: NAD Editorial Submitter: Walter Brown Date: 2005-07-03
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Discussion:
In [tr.rand.req], Paragraph 2 states that "... s is a value of integral type, g is an ... object returning values of unsigned integral type ..."
Proposed resolution:
In 5.1.1 [tr.rand.req], Paragraph 2 replace
... s is a value of integral type, g is an lvalue of a type other than X that defines a zero-argument function object returning values of
unsigned integraltype unsigned long int, ...
In 5.1.1 [tr.rand.seq], Table 16, replace in the line for X(s)
creates an engine with the initial internal state determined by static_cast<unsigned long>(s)
[ Mont Tremblant: Both s and g should be unsigned long. This should refer to the constructor signatures. Jens provided wording post Mont Tremblant. ]
[ Berlin: N1932 adopts the proposed resolution: see 26.3.1.3/1e and Table 3 row 2. Moved to Ready. ]
Rationale:
Jens: Just requiring X(unsigned long) still makes it possible for an evil library writer to also supply a X(int) that does something unexpected. The wording above requires that X(s) always performs as if X(unsigned long) would have been called. I believe that is sufficient and implements our intentions from Mont Tremblant. I see no additional use in actually requiring a X(unsigned long) signature. u.seed(s) is covered by its reference to X(s), same arguments.
[ Portland: Subsumed by N2111. ]
Section: 26.4 [rand], TR1 5.1.3 [tr.rand.var] Status: NAD Submitter: Walter Brown Date: 2005-07-03
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Discussion:
Paragraph 3 requires that template argument U (which corresponds to template parameter Engine) satisfy all uniform random number generator requirements. However, there is no analogous requirement regarding the template argument that corresponds to template parameter Distribution. We believe there should be, and that it should require that this template argument satisfy all random distribution requirements.
Proposed resolution:
Consequence 1: Remove the precondition clauses [tr.rand.var]/16 and /18.
Consequence 2: Add max() and min() functions to those distributions that do not already have them.
[ Mont Tremblant: Jens reccommends NAD, min/max not needed everywhere. Marc supports having min and max to satisfy generic programming interface. ]
Rationale:
Berlin: N1932 makes this moot: variate_generator has been eliminated.
Section: 26.4.8.1 [rand.dist.uni], TR1 5.1.7.1 [tr.rand.dist.iunif] Status: NAD Submitter: Walter Brown Date: 2005-07-03
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Discussion:
In [tr.rand.dist.iunif] the uniform_int distribution currently has a single template parameter, IntType, used as the input_type and as the result_type of the distribution. We believe there is no reason to conflate these types in this way.
Proposed resolution:
We recommend that there be a second template parameter to reflect the distribution's input_type, and that the existing first template parameter continue to reflect (solely) the result_type:
template< class IntType = int, UIntType = unsigned int >
class uniform_int
{
public:
// types
typedef UIntType input_type;
typedef IntType result_type;
[ Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been eliminated. ]
Section: 26.4.8.2 [rand.dist.bern], TR1 5.1.7.2 [tr.rand.dist.bern] Status: NAD Submitter: Walter Brown Date: 2005-07-03
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Discussion:
In [tr.rand.dist.bern] the distribution currently requires;
typedef int input_type;
Proposed resolution:
We believe this is an unfortunate choice, and recommend instead:
typedef unsigned int input_type;
[ Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been eliminated. ]
Section: 26.4.8 [rand.dist], TR1 5.1.7.5 [tr.rand.dist.bin] Status: NAD Submitter: Walter Brown Date: 2005-07-03
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Discussion:
Unlike all other distributions in TR1, this binomial_distribution has an implementation-defined input_type. We believe this is an unfortunate choice, because it hinders users from writing portable code. It also hinders the writing of compliance tests. We recommend instead:
typedef RealType input_type;
While this choice is somewhat arbitrary (as it was for some of the other distributions), we make this particular choice because (unlike all other distributions) otherwise this template would not publish its RealType argument and so users could not write generic code that accessed this second template parameter. In this respect, the choice is consistent with the other distributions in TR1.
We have two reasons for recommending that a real type be specified instead. One reason is based specifically on characteristics of binomial distribution implementations, while the other is based on mathematical characteristics of probability distribution functions in general.
Implementations of binomial distributions commonly use Stirling approximations for values in certain ranges. It is far more natural to use real values to represent these approximations than it would be to use integral values to do so. In other ranges, implementations reply on the Bernoulli distribution to obtain values. While TR1's bernoulli_distribution::input_type is specified as int, we believe this would be better specified as double.
This brings us to our main point: The notion of a random distribution rests on the notion of a cumulative distribution function, which in turn mathematically depends on a continuous dependent variable. Indeed, such a distribution function would be meaningless if it depended on discrete values such as integers - and this remains true even if the distribution function were to take discrete steps.
Although this note is specifically about binomial_distribution::input_type, we intend to recommend that all of the random distributions input_types be specified as a real type (either a RealType template parameter, or double, as appropriate).
Of the nine distributions in TR1, four already have this characteristic (uniform_real, exponential_distribution, normal_distribution, and gamma_distribution). We have already argued the case for the binomial the remaining four distributions.
In the case of uniform_int, we believe that the calculations to produce an integer result in a specified range from an integer in a different specified range is best done using real arithmetic. This is because it involves a product, one of whose terms is the ratio of the extents of the two ranges. Without real arithmetic, the results become less uniform: some numbers become more (or less) probable that they should be. This is, of course, undesireable behavior in a uniform distribution.
Finally, we believe that in the case of the bernoulli_distribution (briefly mentioned earlier), as well as the cases of the geometric_distribution and the poisson_distribution, it would be far more natural to have a real input_type. This is because the most natural computation involves the random number delivered and the distribution's parameter p (in the case of bernoulli_distribution, for example, the computation is a comparison against p), and p is already specified in each case as having some real type.
Proposed resolution:
typedef RealType input_type;
[ Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been eliminated. ]
Section: 26.4.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] Status: NAD Editorial Submitter: Walter Brown Date: 2005-07-03
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Discussion:
Paragraph 8 specifies the algorithm by which a subtract_with_carry_01 engine is to be seeded given a single unsigned long. This algorithm is seriously flawed in the case where the engine parameter w (also known as word_size) exceeds 31 [bits]. The key part of the paragraph reads:
sets x(-r) ... x(-1) to (lcg(1)*2**(-w)) mod 1
and so forth.
Since the specified linear congruential engine, lcg, delivers numbers with a maximum of 2147483563 (just a shade under 31 bits), then when w is, for example, 48, each of the x(i) will be less than 2**-17. The consequence is that roughly the first 400 numbers delivered will be conspicuously close to either zero or one.
Unfortunately, this is not an innocuous flaw: One of the predefined engines in [tr.rand.predef], namely ranlux64_base_01, has w = 48 and would exhibit this poor behavior, while the original N1378 proposal states that these pre-defined engines are intended to be of "known good properties."
Proposed resolution:
In 5.1.4.4 [tr.rand.eng.sub1], replace the "effects" clause for void seed(unsigned long value = 19780503) by
Effects: If value == 0, sets value to 19780503. In any case,
with a linear congruential generator lcg(i) having parameters mlcg = 2147483563, alcg = 40014, clcg = 0, and lcg(0) = value,sets carry(-1) and x(-r) … x(-1) as if executinglinear_congruential<unsigned long, 40014, 0, 2147483563> lcg(value); seed(lcg);
to (lcg(1) · 2-w) mod 1 … (lcg(r) · 2-w) mod 1, respectively. If x(-1) == 0, sets carry(-1) = 2-w, else sets carry(-1) = 0.
[ Jens provided revised wording post Mont Tremblant. ]
[ Berlin: N1932 adopts the originally-proposed resolution of the issue. Jens's supplied wording is a clearer description of what is intended. Moved to Ready. ]
Rationale:
Jens: I'm using an explicit type here, because fixing the prose would probably not qualify for the (with issue 504 even stricter) requirements we have for seed(Gen&).
[ Portland: Subsumed by N2111. ]
Section: 26.4.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] Status: NAD Editorial Submitter: Walter Brown Date: 2005-07-03
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Discussion:
Paragraph 3 begins:
The size of the state is r.
However, this is not quite consistent with the remainder of the paragraph which specifies a total of nr+1 items in the textual representation of the state. We recommend the sentence be corrected to match:
The size of the state is nr+1.
To give meaning to the coefficient n, it may be also desirable to move n's definition from later in the paragraph. Either of the following seem reasonable formulations:
With n=..., the size of the state is nr+1.
The size of the state is nr+1, where n=... .
Proposed resolution:
[ Jens: I plead for "NAD" on the grounds that "size of state" is only used as an argument for big-O complexity notation, thus constant factors and additions don't count. ]
[ Berlin: N1932 adopts the proposed NAD. ]
Section: 26.4.3.3 [rand.eng.sub], TR1 5.1.4.3 [tr.rand.eng.sub] Status: NAD Editorial Submitter: Walter Brown Date: 2005-07-03
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Discussion:
Paragraph 2 begins:
The size of the state is r.
However, the next sentence specifies a total of r+1 items in the textual representation of the state, r specific x's as well as a specific carry. This makes a total of r+1 items that constitute the size of the state, rather than r.
Proposed resolution:
We recommend the sentence be corrected to match:
The size of the state is r+1.
[ Jens: I plead for "NAD" on the grounds that "size of state" is only used as an argument for big-O complexity notation, thus constant factors and additions don't count. ]
[ Berlin: N1932 adopts the proposed NAD. ]
Section: 26.4.2 [rand.synopsis], TR1 5.1.2 [tr.rand.synopsis] Status: NAD Submitter: Walter Brown Date: 2005-07-03
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Discussion:
To accompany the concept of a pseudo-random number engine as defined in Table 17, we propose and recommend an adjunct template, engine_traits, to be declared in [tr.rand.synopsis] as:
template< class PSRE > class engine_traits;
This template's primary purpose would be as an aid to generic programming involving pseudo-random number engines. Given only the facilities described in tr1, it would be very difficult to produce any algorithms involving the notion of a generic engine. The intent of this proposal is to provide, via engine_traits<>, sufficient descriptive information to allow an algorithm to employ a pseudo-random number engine without regard to its exact type, i.e., as a template parameter.
For example, today it is not possible to write an efficient generic function that requires any specific number of random bits. More specifically, consider a cryptographic application that internally needs 256 bits of randomness per call:
template< class Eng, class InIter, class OutIter > void crypto( Eng& e, InIter in, OutIter out );
Without knowning the number of bits of randomness produced per call to a provided engine, the algorithm has no means of determining how many times to call the engine.
In a new section [tr.rand.eng.traits], we proposed to define the engine_traits template as:
template< class PSRE >
class engine_traits
{
static std::size_t bits_of_randomness = 0u;
static std::string name() { return "unknown_engine"; }
// TODO: other traits here
};
Further, each engine described in [tr.rand.engine] would be accompanied by a complete specialization of this new engine_traits template.
Proposed resolution:
[ Berlin: Walter: While useful for implementation per TR1, N1932 has no need for this feature. Recommend close as NAD. ]
Rationale:
Recommend NAD, N1932, N2111 covers this. Already in WP.
Section: 26.4.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] Status: NAD Editorial Submitter: Walter Brown Date: 2005-07-03
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Discussion:
Paragraph 6 says:
... obtained by successive invocations of g, ...
We recommend instead:
... obtained by taking successive invocations of g mod 2**32, ...
as the context seems to require only 32-bit quantities be used here.
Proposed resolution:
Berlin: N1932 adopts the proposed resultion: see 26.3.3.4/7. Moved to Ready.
[ Portland: Subsumed by N2111. ]
Section: 26.4.1 [rand.req], TR1 5.1.1 [tr.rand.req] Status: NAD Submitter: Walter Brown Date: 2005-07-03
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Discussion:
The last two rows of Table 16 deal with the i/o requirements of an engine, specifying that the textual representation of an engine's state, appropriately formatted, constitute the engine's external representation.
This seems adequate when an engine's type is known. However, it seems inadequate in the context of generic code, where it becomes useful and perhaps even necessary to determine an engine's type via input.
Proposed resolution:
We therefore recommend that, in each of these two rows of Table 16, the text "textual representation" be expanded so as to read "engine name followed by the textual representation."
[ Berlin: N1932 considers this NAD. This is a QOI issue. ]
Section: 20.5.4 [meta.unary], TR1 4.5 [tr.meta.unary] Status: NAD Editorial Submitter: Robert Klarer Date: 2005-07-11
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Discussion:
It is not completely clear how the primary type traits deal with cv-qualified types. And several of the secondary type traits seem to be lacking a definition.
[ Berlin: Howard to provide wording. ]
Proposed resolution:
Wording provided in N2028. A revision (N2157) provides more detail for motivation.
Rationale:
Solved by revision (N2157) in the WP.Section: 23.1.3 [sequence.reqmts] Status: NAD Submitter: Chris Jefferson Date: 2005-09-14
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Discussion:
Problem: There are a number of places in the C++ standard library where it is possible to write what appear to be sensible ways of calling functions, but which can cause problems in some (or all) implementations, as they cause the values given to the function to be changed in a way not specified in standard (and therefore not coded to correctly work). These fall into two similar categories.
1) Parameters taken by const reference can be changed during execution of the function
Examples:
Given std::vector<int> v:
v.insert(v.begin(), v[2]);
v[2] can be changed by moving elements of vector
Given std::list<int> l:
l.remove(*l.begin());
Will delete the first element, and then continue trying to access it. This is particularily vicious, as it will appear to work in almost all cases.
2) A range is given which changes during the execution of the function: Similarly,
v.insert(v.begin(), v.begin()+4, v.begin()+6);
This kind of problem has been partly covered in some cases. For example std::copy(first, last, result) states that result cannot be in the range [first, last). However, does this cover the case where result is a reverse_iterator built from some iterator in the range [first, last)? Also, std::copy would still break if result was reverse_iterator(last + 1), yet this is not forbidden by the standard
Solution:
One option would be to try to more carefully limit the requirements of each function. There are many functions which would have to be checked. However as has been shown in the std::copy case, this may be difficult. A simpler, more global option would be to somewhere insert text similar to:
If the execution of any function would change either any values passed by reference or any value in any range passed to a function in a way not defined in the definition of that function, the result is undefined.
Such code would have to at least cover chapters 23 and 25 (the sections I read through carefully). I can see no harm on applying it to much of the rest of the standard.
Some existing parts of the standard could be improved to fit with this, for example the requires for 25.2.1 (Copy) could be adjusted to:
Requires: For each non-negative integer n < (last - first), assigning to *(result + n) must not alter any value in the range [first + n, last).
However, this may add excessive complication.
One other benefit of clearly introducing this text is that it would allow a number of small optimisations, such as caching values passed by const reference.
Matt Austern adds that this issue also exists for the insert and erase members of the ordered and unordered associative containers.
[ Berlin: Lots of controversey over how this should be solved. Lots of confusion as to whether we're talking about self referencing iterators or references. Needs a good survey as to the cases where this matters, for which implementations, and how expensive it is to fix each case. ]
Proposed resolution:
Rationale:
Recommend NAD.
Section: 23.4 [unord], TR1 6.3.4 [tr.unord.unord] Status: NAD Submitter: Paolo Carlini Date: 2005-10-12
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Discussion:
while implementing the resolution of issue 6.19 I'm noticing the following: according to 6.3.4.3/2 (and 6.3.4.5/2), for unordered_set and unordered_multiset:
"The iterator and const_iterator types are both const types. It is unspecified whether they are the same type"
Now, according to the resolution of 6.19, we have overloads of insert with hint and erase (single and range) both for iterator and const_iterator, which, AFAICS, can be meaningful at the same time *only* if iterator and const_iterator *are* in fact different types.
Then, iterator and const_iterator are *required* to be different types? Or that is an unintended consequence? Maybe the overloads for plain iterators should be added only to unordered_map and unordered_multimap? Or, of course, I'm missing something?
Proposed resolution:
Add to 6.3.4.3p2 (and 6.3.4.5p2):
2 ... The iterator and const_iterator types are both const
constant iterator types.
It is unspecified whether they are the same type.
Add a new subsection to 17.4.4 [lib.conforming]:
An implementation shall not supply an overloaded function signature specified in any library clause if such a signature would be inherently ambiguous during overload resolution due to two library types referring to the same type.
[Note: For example, this occurs when a container's iterator and const_iterator types are the same. -- end note]
[ Post-Berlin: Beman supplied wording. ]
Rationale:
Toronto: The first issue has been fixed by N2350 (the insert and erase members are collapsed into one signature). Alisdair to open a separate issue on the chapter 17 wording.Section: 17.4.3.10 [res.on.required] Status: NAD Editorial Submitter: David Abrahams Date: 2005-10-25
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Discussion:
17.4.3.8/1 says:
Violation of the preconditions specified in a function's Required behavior: paragraph results in undefined behavior unless the function's Throws: paragraph specifies throwing an exception when the precondition is violated.
This implies that a precondition violation can lead to defined behavior. That conflicts with the only reasonable definition of precondition: that a violation leads to undefined behavior. Any other definition muddies the waters when it comes to analyzing program correctness, because precondition violations may be routinely done in correct code (e.g. you can use std::vector::at with the full expectation that you'll get an exception when your index is out of range, catch the exception, and continue). Not only is it a bad example to set, but it encourages needless complication and redundancy in the standard. For example:
21 Strings library 21.3.3 basic_string capacity void resize(size_type n, charT c); 5 Requires: n <= max_size() 6 Throws: length_error if n > max_size(). 7 Effects: Alters the length of the string designated by *this as follows:
The Requires clause is entirely redundant and can be dropped. We could make that simplifying change (and many others like it) even without changing 17.4.3.8/1; the wording there just seems to encourage the redundant and error-prone Requires: clause.
[ Batavia: Alan and Pete to work. ]
[ Bellevue: NAD Editorial, this group likes N2121, Pete agrees, accepting it is Pete's business. General agreement that precondition violations are synonymous with UB. ]
Proposed resolution:
1. Change 17.4.3.8/1 to read:
Violation of the preconditions specified in a function's Required behavior: paragraph results in undefined behavior
unless the function's Throws: paragraph specifies throwing an exception when the precondition is violated.
2. Go through and remove redundant Requires: clauses. Specifics to be provided by Dave A.
[ Berlin: The LWG requests a detailed survey of part 2 of the proposed resolution. ]
[ Alan provided the survey N2121. ]
Section: 20.4.1.6 [tuple.rel], TR1 6.1.3.5 [tr.tuple.rel] Status: Pending NAD Editorial Submitter: David Abrahams Date: 2005-11-29
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Duplicate of: 348
Discussion:
Where possible, tuple comparison operators <,<=,=>, and > ought to be defined in terms of std::less rather than operator<, in order to support comparison of tuples of pointers.
Proposed resolution:
change 6.1.3.5/5 from:
Returns: The result of a lexicographical comparison between t and u. The result is defined as: (bool)(get<0>(t) < get<0>(u)) || (!(bool)(get<0>(u) < get<0>(t)) && ttail < utail), where rtail for some tuple r is a tuple containing all but the first element of r. For any two zero-length tuples e and f, e < f returns false.
to:
Returns: The result of a lexicographical comparison between t and u. For any two zero-length tuples e and f, e < f returns false. Otherwise, the result is defined as: cmp( get<0>(t), get<0>(u)) || (!cmp(get<0>(u), get<0>(t)) && ttail < utail), where rtail for some tuple r is a tuple containing all but the first element of r, and cmp(x,y) is an unspecified function template defined as follows.
Where T is the type of x and U is the type of y:
if T and U are pointer types and T is convertible to U, returns less<U>()(x,y)
otherwise, if T and U are pointer types, returns less<T>()(x,y)
otherwise, returns (bool)(x < y)
[ Berlin: This issue is much bigger than just tuple (pair, containers, algorithms). Dietmar will survey and work up proposed wording. ]
Rationale:
Recommend NAD. This will be fixed with the next revision of concepts.
Section: 23.1 [container.requirements] Status: Dup Submitter: Joaquín M López Muñoz Date: 2005-12-17
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Duplicate of: 589
Discussion:
The iterator constructor X(i,j) for containers as defined in 23.1.1 and 23.2.2 does only require that i and j be input iterators but nothing is said about their associated value_type. There are three sensible options:
The issue has practical implications, and stdlib vendors have taken divergent approaches to it: Dinkumware follows 2, libstdc++ follows 3.
The same problem applies to the definition of insert(p,i,j) for sequences and insert(i,j) for associative contianers, as well as assign.
[ The following added by Howard and the example code was originally written by Dietmar. ]
Valid code below?
#include <vector>
#include <iterator>
#include <iostream>
struct foo
{
explicit foo(int) {}
};
int main()
{
std::vector<int> v_int;
std::vector<foo> v_foo1(v_int.begin(), v_int.end());
std::vector<foo> v_foo2((std::istream_iterator<int>(std::cin)),
std::istream_iterator<int>());
}
[ Berlin: Some support, not universal, for respecting the explicit qualifier. ]
Proposed resolution:
Section: C.2 [diff.library] Status: NAD Editorial Submitter: Martin Sebor Date: 2005-11-25
View all issues with NAD Editorial status.
Discussion:
According to C.2.2.3, p1, "the macro NULL, defined in any of <clocale>, <cstddef>, <cstdio>, <cstdlib>, <cstring>, <ctime>, or <cwchar>." This is consistent with the C standard.
However, Table 95 in C.2 fails to mention <clocale> and <cstdlib>.
In addition, C.2, p2 claims that "The C++ Standard library provides 54 standard macros from the C library, as shown in Table 95." While table 95 does have 54 entries, since a couple of them (including the NULL macro) are listed more than once, the actual number of macros defined by the C++ Standard Library may not be 54.
Proposed resolution:
I propose we add <clocale> and <cstdlib> to Table 96 and remove the number of macros from C.2, p2 and reword the sentence as follows:
The C++ Standard library
provides 54 standard macros fromdefines a number macros corresponding to those defined by the C Standard library, as shown in Table 96.
[ Portland: Resolution is considered editorial. It will be incorporated into the WD. ]
Section: 26.4 [rand], TR1 5.1 [tr.rand] Status: NAD Submitter: Matt Austern Date: 2006-01-10
View all other issues in [rand].
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Discussion:
Paragraph 10 describes how a variate generator uses numbers produced by an engine to pass to a generator. The sentence that concerns me is: "Otherwise, if the value for engine_value_type::result_type is true and the value for Distribution::input_type is false [i.e. if the engine produces integers and the engine wants floating-point values], then the numbers in s_eng are divided by engine().max() - engine().min() + 1 to obtain the numbers in s_e." Since the engine is producing integers, both the numerator and the denominator are integers and we'll be doing integer division, which I don't think is what we want. Shouldn't we be performing a conversion to a floating-point type first?
Proposed resolution:
Rationale:
Recommend NAD as the affected section is now gone and so the issue is moot. N2111.
Section: 26.4.6 [rand.device], TR1 5.1.6 [tr.rand.device] Status: NAD Submitter: Matt Austern Date: 2006-01-10
View all issues with NAD status.
Discussion:
Class random_device "produces non-deterministic random numbers", using some external source of entropy. In most real-world systems, the amount of available entropy is limited. Suppose that entropy has been exhausted. What is an implementation permitted to do? In particular, is it permitted to block indefinitely until more random bits are available, or is the implementation required to detect failure immediately? This is not an academic question. On Linux a straightforward implementation would read from /dev/random, and "When the entropy pool is empty, reads to /dev/random will block until additional environmental noise is gathered." Programmers need to know whether random_device is permitted to (or possibly even required to?) behave the same way.
[ Berlin: Walter: N1932 considers this NAD. Does the standard specify whether std::cin may block? ]
See N2391 and N2423 for some further discussion.
Proposed resolution:
Adopt the proposed resolution in N2423 (NAD).
Section: 26.4.8 [rand.dist], TR1 5.1.7.5 [tr.rand.dist.bin] Status: NAD Editorial Submitter: Matt Austern Date: 2006-01-10
View all other issues in [rand.dist].
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Discussion:
Paragraph 1 says that "A binomial distributon random distribution produces integer values i>0 with p(i) = (n choose i) * p*i * (1-p)^(t-i), where t and p are the parameters of the distribution. OK, that tells us what t, p, and i are. What's n?
Proposed resolution:
Berlin: Typo: "n" replaced by "t" in N1932: see 26.3.7.2.2/1.
[ Portland: Subsumed by N2111. ]
Section: 18.3.1 [cstdint.syn], TR1 8.22.1 [tr.c99.cstdint.syn] Status: NAD Editorial Submitter: Paolo Carlini Date: 2006-01-30
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Discussion:
In the synopsis, some types are identified as optional: int8_t, int16_t, and so on, consistently with C99, indeed.
On the other hand, intptr_t and uintptr_t, are not marked as such and probably should, consistently with C99, 7.18.1.4.
Proposed resolution:
Change 18.3.1 [cstdint.syn]:
... typedef signed integer type intptr_t; // optional ... typedef unsigned integer type uintptr_t; // optional ...
Rationale:
Recommend NAD and fix as editorial with the proposed resolution.Section: 18.2.1.5 [numeric.special] Status: NAD Submitter: Howard Hinnant Date: 2006-01-29
View all other issues in [numeric.special].
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Discussion:
I believe we have a bug in the resolution of: lwg 184 (WP status).
The resolution spells out each member of numeric_limits<bool>. The part I'm having a little trouble with is:
static const bool traps = false;
Should this not be implementation defined? Given:
int main()
{
bool b1 = true;
bool b2 = false;
bool b3 = b1/b2;
}
If this causes a trap, shouldn't numeric_limits<bool>::traps be true?
Proposed resolution:
Change 18.2.1.5p3:
-3- The specialization for bool shall be provided as follows:
namespace std { template <> class numeric_limits<bool> { ... static const bool traps =falseimplementation-defined; ... }; }
[ Redmond: NAD because traps refers to values, not operations. There is no bool value that will trap. ]
Section: TR1 8.21 [tr.c99.boolh] Status: NAD Editorial Submitter: Paolo Carlini Date: 2006-02-02
View all issues with NAD Editorial status.
Discussion:
This one, if nobody noticed it yet, seems really editorial: s/cstbool/cstdbool/
Proposed resolution:
Change 8.21p1:
-1- The header behaves as if it defines the additional macro defined in <cstdbool> by including the header <cstdbool>.
[ Redmond: Editorial. ]
Section: 18.3 [cstdint], TR1 8.22 [tr.c99.cstdint] Status: NAD Editorial Submitter: Paolo Carlini Date: 2006-02-06
View all other issues in [cstdint].
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Discussion:
I'm seeing a problem with such overloads: when, _Longlong == intmax_t == long long we end up, essentially, with the same arguments and different return types (lldiv_t and imaxdiv_t, respectively). Similar issue with abs(_Longlong) and abs(intmax_t), of course.
Comparing sections 8.25 and 8.11, I see an important difference, however: 8.25.3 and 8.25.4 carefully describe div and abs for _Longlong types (rightfully, because not moved over directly from C99), whereas there is no equivalent in 8.11: the abs and div overloads for intmax_t types appear only in the synopsis and are not described anywhere, in particular no mention in 8.11.2 (at variance with 8.25.2).
I'm wondering whether we really, really, want div and abs for intmax_t...
Proposed resolution:
[ Portland: no consensus. ]
Rationale:
[ Batavia, Bill: The <cstdint> synopsis in TR1 8.11.1 [tr.c99.cinttypes.syn] contains: ]
intmax_t imaxabs(intmax_t i); intmax_t abs(intmax_t i); imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom); imaxdiv_t div(intmax_t numer, intmax_t denom);
[ and in TR1 8.11.2 [tr.c99.cinttypes.def]: ]
The header defines all functions, types, and macros the same as C99 subclause 7.8.
[ This is as much definition as we give for most other C99 functions, so nothing need change. We might, however, choose to add the footnote: ]
[Note: These overloads for abs and div may well be equivalent to those that take long long arguments. If so, the implementation is responsible for avoiding conflicting declarations. -- end note]
[ Bellevue: NAD Editorial. Pete must add a footnote, as described below. ]
[ Looks like a real problem. Dietmar suggests div() return a template type. Matt: looks like imaxdiv_t is loosly defined. Can it be a typedef for lldiv_t when _Longlong == intmax_t? PJP seems to agree. We would need a non-normative note declaring that the types lldiv_t and imaxdiv_t may not be unique if intmax_t==_longlong. ]
Section: 24.1.1 [input.iterators] Status: NAD Editorial Submitter: David Abrahams Date: 2006-02-09
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Discussion:
24.1.1 Input iterators [lib.input.iterators]
1 A class or a built-in type X satisfies the requirements of an input iterator for the value type T if the following expressions are valid, where U is the type of any specified member of type T, as shown in Table 73.
There is no capital U used in table 73. There is a lowercase u, but that is clearly not meant to denote a member of type T. Also, there's no description in 24.1.1 of what lowercase a means. IMO the above should have been...Hah, a and b are already covered in 24.1/11, so maybe it should have just been:
Proposed resolution:
Change 24.1.1p1:
-1- A class or a built-in type X satisfies the requirements of an input iterator for the value type T if the following expressions are valid
, where U is the type of any specified member of type T,as shown in Table 73.
[ Portland: Editorial. ]
Section: 20.1.2 [allocator.requirements] Status: NAD Submitter: Sergey P. Derevyago Date: 2006-02-17
View other active issues in [allocator.requirements].
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Discussion:
User-defined allocators without default constructor are not explicitly supported by the standard but they can be supported just like std::vector supports elements without default constructor.
As a result, there exist implementations that work well with such allocators and implementations that don't.
1) The standard doesn't explicitly state this intent but it should. In particular, 20.1.5p5 explicitly state the intent w.r.t. the allocator instances that compare non-equal. So it can similarly state the intent w.r.t. the user-defined allocators without default constructor.
2) Some container operations are obviously underspecified. In particular, 21.3.7.1p2 tells:
template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+( const charT* lhs, const basic_string<charT,traits,Allocator>& rhs );Returns: basic_string<charT,traits,Allocator>(lhs) + rhs.
That leads to the basic_string<charT,traits,Allocator>(lhs, Allocator()) call. Obviously, the right requirement is:
Returns: basic_string<charT,traits,Allocator>(lhs, rhs.get_allocator()) + rhs.
It seems like a lot of DRs can be submitted on this "Absent call to get_allocator()" topic.
1) Explicitly state the intent to allow for user-defined allocators without default constructor in 20.1.5 Allocator requirements.
2) Correct all the places, where a correct allocator object is available through the get_allocator() call but default Allocator() gets passed instead.
Let's suppose that the following memory pool is available:
class mem_pool {
// ...
void* allocate(size_t size);
void deallocate(void* ptr, size_t size);
};
So the following allocator can be implemented via this pool:
class stl_allocator {
mem_pool& pool;
public:
explicit stl_allocator(mem_pool& mp) : pool(mp) {}
stl_allocator(const stl_allocator& sa) : pool(sa.pool) {}
template <class U>
stl_allocator(const stl_allocator<U>& sa) : pool(sa.get_pool()) {}
~stl_allocator() {}
pointer allocate(size_type n, std::allocator<void>::const_pointer = 0)
{
return (n!=0) ? static_cast<pointer>(pool.allocate(n*sizeof(T))) : 0;
}
void deallocate(pointer p, size_type n)
{
if (n!=0) pool.deallocate(p, n*sizeof(T));
}
// ...
};
Then the following code works well on some implementations and doesn't work on another:
typedef basic_string<char, char_traits<char>, stl_allocator<char> >
tl_string;
mem_pool mp;
tl_string s1("abc", stl_allocator<int>(mp));
printf("(%s)\n", ("def"+s1).c_str());
In particular, on some implementations the code can't be compiled without default stl_allocator() constructor.
The obvious way to solve the compile-time problems is to intentionally define a NULL pointer dereferencing default constructor
stl_allocator() : pool(*static_cast<mem_pool*>(0)) {}
in a hope that it will not be called. The problem is that it really gets called by operator+(const char*, const string&) under the current 21.3.7.1p2 wording.
Proposed resolution:
Rationale:
Recommend NAD. operator+() with string already requires the desired semantics of copying the allocator from one of the strings (lhs when there is a choice).
Section: 27.4.4.3 [iostate.flags] Status: Dup Submitter: Seungbeom Kim Date: 2006-03-10
View all other issues in [iostate.flags].
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Duplicate of: 272
Discussion:
Section: 27.4.4.3 [lib.iostate.flags]
Paragraph 4 says:
void clear(iostate state = goodbit);Postcondition: If rdbuf()!=0 then state == rdstate(); otherwise rdstate()==state|ios_base::badbit.
The postcondition "rdstate()==state|ios_base::badbit" is parsed as "(rdstate()==state)|ios_base::badbit", which is probably what the committee meant.
Rationale:
Section: 21.1 [char.traits] Status: NAD Submitter: Jack Reeves Date: 2006-04-06
View all other issues in [char.traits].
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Discussion:
Currently, the Standard Library specifies only a declaration for template class char_traits<> and requires the implementation provide two explicit specializations: char_traits<char> and char_traits<wchar_t>. I feel the Standard should require explicit specializations for all built-in character types, i.e. char, wchar_t, unsigned char, and signed char.
I have put together a paper (N1985) that describes this in more detail and includes all the necessary wording.
[ Portland: Jack will rewrite N1985 to propose a primary template that will work with other integral types. ]
[ Toronto: issue has grown with addition of char16_t and char32_t. ]
[ post Bellevue: ]
We suggest that Jack be asked about the status of his paper, and if it is not forthcoming, the work-item be assigned to someone else. If no one steps forward to do the paper before the next meeting, we propose to make this NAD without further discussion. We leave this Open for now, but our recommendation is NAD.
Note: the issue statement should be updated, as the Toronto comment has already been resolved. E.g., char_traits specializations for char16_t and char32_t are now in the working paper.
[ Sophia Antipolis: ]
Nobody has submitted the requested paper, so we move to NAD, as suggested by the decision at the last meeting.
Proposed resolution:
Section: 1.2 [intro.refs] Status: NAD Editorial Submitter: Beman Dawes Date: 2006-04-08
View all other issues in [intro.refs].
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Discussion:
1.2 Normative references [intro.refs] of the WP currently refers to ISO/IEC 9899:1990, Programming languages - C. Should that be changed to ISO/IEC 9899:1999?
What impact does this have on the library?
Proposed resolution:
In 1.2/1 [intro.refs] of the WP, change:
- ISO/IEC 9899:
19901999 + TC1 + TC2, Programming languages - C
Rationale:
Recommend NAD, fixed editorially.Section: 26.4 [rand], TR1 5.1 [tr.rand] Status: NAD Submitter: Howard Hinnant Date: 2006-04-11
View all other issues in [rand].
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Discussion:
In Berlin, as a working group, we voted in favor of N1932 which makes issue 507 moot: variate_generator has been eliminated. Then in full committee we voted to give this issue WP status (mistakenly).
Proposed resolution:
Strike the proposed resolution of issue 507.
[ post-Portland: Walter and Howard recommend NAD. The proposed resolution of 507 no longer exists in the current WD. ]
Rationale:
NAD. Will be moot once N2135 is adopted.
Section: 23.1.5 [unord.req] Status: NAD Submitter: Joaquín M López Muñoz Date: 2006-06-13
View other active issues in [unord.req].
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Discussion:
See N2023 for full discussion.
Proposed resolution:
Option 1:
The problem can be eliminated by omitting the requirement that a.erase(q) return an iterator. This is, however, in contrast with the equivalent requirements for other standard containers.
Option 2:
a.erase(q) can be made to compute the next iterator only when explicitly requested: the technique consists in returning a proxy object implicitly convertible to iterator, so that
iterator q1=a.erase(q);
works as expected, while
a.erase(q);
does not ever invoke the conversion-to-iterator operator, thus avoiding the associated computation. To allow this technique, some sections of TR1 along the line "return value is an iterator..." should be changed to "return value is an unspecified object implicitly convertible to an iterator..." Although this trick is expected to work transparently, it can have some collateral effects when the expression a.erase(q) is used inside generic code.
Rationale:
N2023 was discussed in Portland and the consensus was that there appears to be no need for either change proposed in the paper. The consensus opinion was that since the iterator could serve as its own proxy, there appears to be no need for the change. In general, "converts to" is undesirable because it interferes with template matching.
Post Toronto: There does not at this time appear to be consensus with the Portland consensus.
[ Bellevue: ]
The Bellevue review of this issue reached consensus with the Portland consensus, in contravention of the Toronto non-consensus. Common implementations have the iterator readily available, and most common uses depend on the iterator being returned.
Section: 26.7 [c.math] Status: NAD Submitter: Beman Dawes Date: 2006-06-15
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Discussion:
There is no div() function for unsigned integer types.
There are several possible resolutions. The simplest one is noted below. Other possibilities include a templated solution.
Proposed resolution:
Add to 26.7 [lib.c.math] paragraph 8:
struct udiv_t div(unsigned, unsigned); struct uldiv_t div(unsigned long, unsigned long); struct ulldiv_t div(unsigned long long, unsigned long long);
Rationale:
Toronto: C99 does not have these unsigned versions because the signed version exist just to define the implementation-defined behavior of signed integer division. Unsigned integer division has no implementation-defined behavior and thus does not need this treatment.Section: 26.7 [c.math] Status: NAD Submitter: Beman Dawes Date: 2006-06-15
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Discussion:
There is no pow() function for any integral type.
Proposed resolution:
Add something like:
template< typename T> T power( T x, int n ); // requires: n >=0
Rationale:
Toronto: We already have double pow(integral, integral) from 26.7 [c.math] p11.Section: D.7.2.1 [depr.istrstream.cons] Status: NAD Editorial Submitter: Martin Sebor Date: 2006-06-22
View all issues with NAD Editorial status.
Discussion:
The iststream(char*, streamsize) ctor is in the class
synopsis in D.7.2 but its signature is missing in the description
below (in D.7.2.1).
Proposed resolution:
This seems like a simple editorial issue and the missing signature can
be added to the one for const char* in paragraph 2.
[ post Oxford: Noted that it is already fixed in N2284 ]
Section: 20.5 [meta], TR1 4.9 [tr.meta.req] Status: NAD Editorial Submitter: Beman Dawes Date: 2006-08-10
View all other issues in [meta].
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Discussion:
20.4.9 [lib.meta.req], Implementation requirements, provides latitude for type traits implementers that is not needed in C++0x. It includes the wording:
[Note: the latitude granted to implementers in this clause is temporary, and is expected to be removed in future revisions of this document. -- end note]
Note: N2157: Minor Modifications to the type traits Wording also has the intent of removing this wording from the WP.
Proposed resolution:
Remove 20.4.9 [lib.meta.req] in its entirety from the WP.
[ post-Oxford: Recommend NAD Editorial. This resolution is now in the current working draft. ]
Section: 18.2.1.2 [numeric.limits.members] Status: NAD Editorial Submitter: whyglinux Date: 2006-08-08
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Discussion:
18.2.1.2 numeric_limits members [lib.numeric.limits.members] Paragraph 7:
"For built-in integer types, the number of non-sign bits in the representation."
26.1 Numeric type requirements [lib.numeric.requirements] Footnote:
"In other words, value types. These include built-in arithmetic types, pointers, the library class complex, and instantiations of valarray for value types."
Integer types (which are bool, char, wchar_t, and the signed and unsigned integer types) and arithmetic types (which are integer and floating types) are all built-in types and thus there are no non-built-in (that is, user-defined) integer or arithmetic types. Since the redundant "built-in" in the above 2 sentences can mislead that there may be built-in or user-defined integer and arithmetic types (which is not correct), the "built-in" should be removed.
Proposed resolution:
18.2.1.2 numeric_limits members [lib.numeric.limits.members] Paragraph 7:
"For
built-ininteger types, the number of non-sign bits in the representation."
26.1 Numeric type requirements [lib.numeric.requirements] Footnote:
"In other words, value types. These include
built-inarithmetic types, pointers, the library class complex, and instantiations of valarray for value types."
Rationale:
Recommend NAD / Editorial. The proposed resolution is accepted as editorial.
Section: 27.8.1.9 [ifstream.members] Status: NAD Editorial Submitter: Christopher Kohlhoff Date: 2006-08-17
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Discussion:
I just spotted a minor problem in 27.8.1.7 [lib.ifstream.members] para 4 and also 27.8.1.13 [lib.fstream.members] para 4. In both places it says:
void close();Effects: Calls rdbuf()->close() and, if that function returns false, ...
However, basic_filebuf::close() (27.8.1.2) returns a pointer to the filebuf on success, null on failure, so I think it is meant to say "if that function returns a null pointer". Oddly, it is correct for basic_ofstream.
Proposed resolution:
Change 27.8.1.9 [ifstream.members], p5:
Effects: Calls rdbuf()->close() and, if that function fails (returns
falsea null pointer), calls setstate(failbit) (which may throw ios_base::failure (27.4.4.3)).
Change 27.8.1.17 [fstream.members], p5:
Effects: Calls rdbuf()->close() and, if that function fails (returns
falsea null pointer), calls setstate(failbit) (which may throw ios_base::failure (27.4.4.3)).
[ Kona (2007): Proposed Disposition: NAD, Editorial ]
Section: 20.1.1 [utility.arg.requirements] Status: Pending NAD Editorial Submitter: Niels Dekker Date: 2006-11-02
View other active issues in [utility.arg.requirements].
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Discussion:
It seems undesirable to define the Swappable requirement in terms of CopyConstructible and Assignable requirements. And likewise, once the MoveConstructible and MoveAssignable requirements (N1860) have made it into the Working Draft, it seems undesirable to define the Swappable requirement in terms of those requirements. Instead, it appears preferable to have the Swappable requirement defined exclusively in terms of the existence of an appropriate swap function.
Section 20.1.4 [lib.swappable] of the current Working Draft (N2009) says:
I can think of three disadvantages of this definition:The Swappable requirement is met by satisfying one or more of the following conditions:
- T is Swappable if T satisfies the CopyConstructible requirements (20.1.3) and the Assignable requirements (23.1);
- T is Swappable if a namespace scope function named swap exists in the same namespace as the definition of T, such that the expression swap(t,u) is valid and has the semantics described in Table 33.
A client might want to stop T from satisfying the Swappable requirement, because swapping by means of copy construction and assignment might throw an exception, and she might find a throwing swap unacceptable for her type. On the other hand, she might not feel the need to fully implement her own swap function for this type. In this case she would want to be able to simply prevent algorithms that would swap objects of type T from being used, e.g., by declaring a swap function for T, and leaving this function purposely undefined. This would trigger a link error, if an attempt would be made to use such an algorithm for this type. For most standard library implementations, this practice would indeed have the effect of stopping T from satisfying the Swappable requirement.
While I'm aware about the fact that people have mixed feelings about providing a specialization of std::swap, it is well-defined to do so. It sounds rather counter-intuitive to say that T is not Swappable, if it has a valid and semantically correct specialization of std::swap. Also in practice, providing such a specialization will have the same effect as satisfying the Swappable requirement.
I'm aware that the intention of the Draft is to prefer calling the swap function of T over doing copy construction and assignments. Still in my opinion, it would be better to make this clear in the wording of the definition of Swappable.
I would like to have the Swappable requirement defined in such a way that the following code fragment will correctly swap two objects of a type T, if and only if T is Swappable:
using std::swap; swap(t, u); // t and u are of type T.
This is also the way Scott Meyers recommends calling a swap function, in Effective C++, Third Edition, item 25.
Most aspects of this issue have been dealt with in a discussion on comp.std.c++ about the Swappable requirement, from 13 September to 4 October 2006, including valuable input by David Abrahams, Pete Becker, Greg Herlihy, Howard Hinnant and others.
Proposed resolution:
Change section 20.1.4 [lib.swappable] as follows:
The Swappable requirement is met by satisfying
one or more of the following conditions:the following condition:
T is Swappable if T satisfies the CopyConstructible requirements (20.1.3) and the Assignable requirements (23.1);T is Swappable if a namespace scope function named swap exists in the same namespace as the definition of T, such that the expression swap(t,u) is valid and has the semantics described in Table 33.T is Swappable if an unqualified function call swap(t,u) is valid within the namespace std, and has the semantics described in Table 33.
Rationale:
Recommend NAD. Concepts, specifically N2082 and N2084, will essentially rewrite this section and provide the desired semantics.
Section: 21.5 [c.strings] Status: NAD Editorial Submitter: Bo Persson Date: 2006-12-11
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Discussion:
In the current draft N2134, 21.4/1 says
"Tables 59,228) 60, 61, 62,and 63 229) 230) describe headers <cctype>, <cwctype>, <cstring>, <cwchar>, and <cstdlib> (character conversions), respectively."
Here footnote 229 applies to table 62, not table 63.
Also, footnote 230 lists the new functions in table 63, "atoll, strtoll, strtoull, strtof, and strtold added by TR1". However, strtof is not present in table 63.
Proposed resolution:
Rationale:
Recommend NAD, editorial. Send to Pete.
Section: 17 [library] Status: Pending NAD Editorial Submitter: Martin Sebor Date: 2007-01-20
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Discussion:
Many member functions of basic_string are overloaded,
with some of the overloads taking a string argument,
others value_type*, others size_type, and
others still iterators. Often, the requirements on one of
the overloads are expressed in the form of Effects,
Throws, and in the Working Paper
(N2134)
also Remark clauses, while those on the rest of the overloads
via a reference to this overload and using a Returns clause.
The difference between the two forms of specification is that per 17.3.1.3 [structure.specifications], p3, an Effects clause specifies "actions performed by the functions," i.e., its observable effects, while a Returns clause is "a description of the return value(s) of a function" that does not impose any requirements on the function's observable effects.
Since only Notes are explicitly defined to be informative and all other paragraphs are explicitly defined to be normative, like Effects and Returns, the new Remark clauses also impose normative requirements.
So by this strict reading of the standard there are some member functions of
basic_string that are required to throw an
exception under some conditions or use specific traits members while
many other otherwise equivalent overloads, while obliged to return the
same values, aren't required to follow the exact same requirements
with regards to the observable effects.
Here's an example of this problem that was precipitated by the change from informative Notes to normative Remarks (presumably made to address 424):
In the Working Paper,
find(string, size_type) contains a
Remark clause (which is just a Note in the current
standard) requiring it to use traits::eq().
find(const charT *s, size_type pos) is specified to
return find(string(s), pos) by a Returns clause
and so it is not required to use traits::eq(). However,
the Working Paper has replaced the original informative Note
about the function using traits::length() with a
normative requirement in the form of a Remark. Calling
traits::length() may be suboptimal, for example when the
argument is a very long array whose initial substring doesn't appear
anywhere in *this.
Here's another similar example, one that existed even prior to the introduction of Remarks:
insert(size_type pos, string, size_type, size_type) is
required to throw out_of_range if pos >
size().
insert(size_type pos, string str) is specified to return
insert(pos, str, 0, npos) by a Returns clause and
so its effects when pos > size() are strictly speaking
unspecified.
I believe a careful review of the current Effects and Returns clauses is needed in order to identify all such problematic cases. In addition, a review of the Working Paper should be done to make sure that the newly introduced normative Remark clauses do not impose any undesirable normative requirements in place of the original informative Notes.
[ Batavia: Alan and Pete to work. ]
[ Bellevue: Marked as NAD Editorial. ]
[ Post-Sophia Antipolis: Martin indicates there is still work to be done on this issue. Reopened. ]
Proposed resolution:
Section: 17.3.1.3 [structure.specifications] Status: NAD Editorial Submitter: Martin Sebor Date: 2007-01-20
View all other issues in [structure.specifications].
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Discussion:
The Remark clauses newly introduced into the Working Paper (N2134) are not mentioned in 17.3.1.3 [structure.specifications] where we list the meaning of Effects, Requires, and other clauses (with the exception of Notes which are documented as informative in 17.3.1.1 [structure.summary], p2, and which they replace in many cases).
Propose add a bullet for Remarks along with a brief description.
[ Batavia: Alan and Pete to work. ]
[ Bellevue: Already resolved in current working paper. ]
Proposed resolution:
Section: 18.5.1.1 [new.delete.single] Status: NAD Submitter: P.J. Plauger Date: 2007-01-23
View all other issues in [new.delete.single].
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Discussion:
I recognize the need for nothrow guarantees in the exception reporting mechanism, but I strongly believe that implementors also need an escape hatch when memory gets really low. (Like, there's not enough heap to construct and copy exception objects, or not enough stack to process the throw.) I'd like to think we can put this escape hatch in 18.5.1.1 [new.delete.single], operator new, but I'm not sure how to do it. We need more than a footnote, but the wording has to be a bit vague. The idea is that if new can't allocate something sufficiently small, it has the right to abort/call terminate/call unexpected.
[ Bellevue: NAD. 1.4p2 specifies a program must behave correctly "within its resource limits", so no further escape hatch is necessary. ]
Proposed resolution:
Section: 20.6.15.2.5 [func.wrap.func.targ] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-02-03
View all issues with NAD Editorial status.
Discussion:
20.6.15.2.5 [func.wrap.func.targ], p4 says:
Returns: If type() == typeid(T), a pointer to the stored function target; otherwise a null pointer.
Proposed resolution:
Change 20.6.15.2.5 [func.wrap.func.targ], p4:
Returns: If
type()target_type() == typeid(T) && typeid(T) != typeid(void), a pointer to the stored function target; otherwise a null pointer.
[ Pete: Agreed. It's editorial, so I'll fix it. ]
Section: 26.5.2.3 [valarray.access] Status: NAD Editorial Submitter: Bo Persson Date: 2007-02-11
View all other issues in [valarray.access].
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Discussion:
The signature of the const operator[] has been changed to return a const reference.
The description in paragraph 1 still says that the operator returns by value.
[ Pete recommends editorial fix. ]
Proposed resolution:
Section: 26.7 [c.math] Status: NAD Editorial Submitter: Bo Persson Date: 2007-02-13
View all other issues in [c.math].
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Discussion:
26.7 [c.math], paragraph 10 has long lists of added signatures for float and long double functions. All the signatures have float/long double return values, which is inconsistent with some of the double functions they are supposed to overload.
Proposed resolution:
Change 26.7 [c.math], paragraph 10,
floatint ilogb(float);floatlong lrint(float);floatlong lround(float);floatlong long llrint(float);floatlong long llround(float);long doubleint ilogb(long double);long doublelong lrint(long double);long doublelong lround(long double);long doublelong long llrint(long double);long doublelong long llround(long double);
Section: 27.6.1.2.3 [istream::extractors], 27.6.2.6.3 [ostream.inserters] Status: NAD Submitter: Daniel Krügler Date: 2007-02-17
View all other issues in [istream::extractors].
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Discussion:
There already exist two active DR's for the wording of 27.6.1.2.3 [istream::extractors]/13 from 14882:2003(E), namely 64 and 413.
Even with these proposed corrections, already maintained in N2134, I have the feeling, that the current wording does still not properly handle the "exceptional" situation. The combination of para 14
"[..] Characters are extracted and inserted until any of the following occurs:
[..]
- an exception occurs (in which case the exception is caught)."
and 15
"If the function inserts no characters, it calls setstate(failbit), which may throw ios_base::failure (27.4.4.3). If it inserted no characters because it caught an exception thrown while extracting characters from *this and failbit is on in exceptions() (27.4.4.3), then the caught exception is rethrown."
both in N2134 seems to imply that any exception, which occurs *after* at least one character has been inserted is caught and lost for ever. It seems that even if failbit is on in exceptions() rethrow is not allowed due to the wording "If it inserted no characters because it caught an exception thrown while extracting".
Is this behaviour by design?
I would like to add that its output counterpart in 27.6.2.6.3 [ostream.inserters]/7-9 (also N2134) does not demonstrate such an exception-loss-behaviour. On the other side, I wonder concerning several subtle differences compared to input::
1) Paragraph 8 says at its end:
"- an exception occurs while getting a character from sb."
Note that there is nothing mentioned which would imply that such an exception will be caught compared to 27.6.1.2.3 [istream::extractors]/14.
2) Paragraph 9 says:
"If the function inserts no characters, it calls setstate(failbit) (which may throw ios_base::failure (27.4.4.3)). If an exception was thrown while extracting a character, the function sets failbit in error state, and if failbit is on in exceptions() the caught exception is rethrown."
The sentence starting with "If an exception was thrown" seems to imply that such an exception *should* be caught before.
Proposed resolution:
(a) In 27.6.1.2.3 [istream::extractors]/15 (N2134) change the sentence
If the function inserts no characters, it calls setstate(failbit), which may throw ios_base::failure (27.4.4.3). If
it inserted no characters because it caught an exception thrown while extracting characters from *thisan exception was thrown while extracting a character from *this, the function sets failbit in error state, and failbit is on in exceptions() (27.4.4.3), then the caught exception is rethrown.
(b) In 27.6.2.6.3 [ostream.inserters]/8 (N2134) change the sentence:
Gets characters from sb and inserts them in *this. Characters are read from sb and inserted until any of the following occurs:
- end-of-file occurs on the input sequence;
- inserting in the output sequence fails (in which case the character to be inserted is not extracted);
- an exception occurs while getting a character from sb (in which case the exception is caught).
Rationale:
This extractor is described as a formatted input function so the exception behavior is already specified. There is additional behavior described in this section that applies to the case in which failbit is set. This doesn't contradict the usual exception behavior for formatted input functions because that applies to the case in which badbit is set.Section: 27.6.4 [ext.manip] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-02-18
View other active issues in [ext.manip].
View all other issues in [ext.manip].
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Discussion:
The function f in para 4 (27.6.4 [ext.manip]) references an unknown strm in the following line:
mg.get(Iter(str.rdbuf()), Iter(), intl, strm, err, mon);
Proposed resolution:
Change 27.6.4 [ext.manip], p4:
mg.get(Iter(str.rdbuf()), Iter(), intl, strm, err, mon);
[ Oxford: Editorial. ]
Section: 27.8.1.9 [ifstream.members], 27.8.1.13 [ofstream.members] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-02-20
View all other issues in [ifstream.members].
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Discussion:
The standard wording of N2134 has extended the 14882:2003(E) wording for the ifstream/ofstream/fstream open function to fix a long standing problem, see 409.
Now it's properly written as
"If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit)[..]"
instead of the previous
"If that function returns a null pointer, calls setstate(failbit)[..]
While the old footnotes saying
"A successful open does not change the error state."
where correct and important, they are invalid now for ifstream and ofstream (because clear *does* indeed modify the error state) and should be removed (Interestingly fstream itself never had these, although they where needed for that time).
Proposed resolution:
In 27.8.1.9 [ifstream.members], remove footnote:
334) A successful open does not change the error state.
In 27.8.1.13 [ofstream.members], remove footnote:
335) A successful open does not change the error state.
Section: 28.10 [re.results] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-02-26
View all other issues in [re.results].
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Discussion:
According to the description given in 28.10 [re.results]/2 the class template match_results "shall satisfy the requirements of a Sequence, [..], except that only operations defined for const-qualified Sequences are supported". Comparing the provided operations from 28.10 [re.results]/3 with the sequence/container tables 80 and 81 one recognizes the following missing operations:
1) The members
const_iterator rbegin() const; const_iterator rend() const;
should exists because 23.1/10 demands these for containers (all sequences are containers) which support bidirectional iterators. Aren't these supported by match_result? This is not explicitely expressed, but it's somewhat implied by two arguments:
(a) Several typedefs delegate to iterator_traits<BidirectionalIterator>.
(b) The existence of const_reference operator[](size_type n) const implies even random-access iteration. I also suggest, that match_result should explicitly mention, which minimum iterator category is supported and if this does not include random-access the existence of operator[] is somewhat questionable.
2) The new "convenience" members
const_iterator cbegin() const; const_iterator cend() const; const_iterator crbegin() const; const_iterator crend() const;
should be added according to tables 80/81.
Proposed resolution:
Add the following members to the match_results synopsis after end() in 28.10 [re.results] para 3:
const_iterator cbegin() const; const_iterator cend() const;
In section 28.10.3 [re.results.acc] change:
const_iterator begin() const; const_iterator cbegin() const;-7- Returns: A starting iterator that enumerates over all the sub-expressions stored in *this.
const_iterator end() const; const_iterator cend() const;-8- Returns: A terminating iterator that enumerates over all the sub-expressions stored in *this.
[ Kona (2007): Voted to adopt proposed wording in N2409 except removing the entry in the table container requirements. Moved to Review. ]
[ Bellevue: Proposed wording now in the WP. ]
Section: 28.11.3 [re.alg.search] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-02-26
View all issues with NAD Editorial status.
Discussion:
28.11.3 [re.alg.search]/5 declares
template <class iterator, class charT, class traits>
bool regex_search(iterator first, iterator last,
const basic_regex<charT, traits>& e,
regex_constants::match_flag_type flags =
regex_constants::match_default);
where it's not explained, which iterator category the parameter iterator belongs to. This is inconsistent to the preceding declaration in the synopsis section 28.4 [re.syn], which says:
template <class BidirectionalIterator, class charT, class traits>
bool regex_search(BidirectionalIterator first, BidirectionalIterator last,
const basic_regex<charT, traits>& e,
regex_constants::match_flag_type flags =
regex_constants::match_default);
Proposed resolution:
In 28.11.3 [re.alg.search]/5 replace all three occurences of param "iterator" with "BidirectionalIterator"
template <classiteratorBidirectionalIterator, class charT, class traits> bool regex_search(iteratorBidirectionalIterator first,iteratorBidirectionalIterator last, const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);-6- Effects: Behaves "as if" by constructing an object what of type match_results<
iteratorBidirectionalIterator> and then returning the result of regex_search(first, last, what, e, flags).
Rationale:
Applied to working paper while issue was still in New status.Section: 28.12.1.1 [re.regiter.cnstr] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-03-03
View all issues with NAD Editorial status.
Discussion:
In 28.12.1.1 [re.regiter.cnstr]/2 the effects paragraph starts with:
Effects: Initializes begin and end to point to the beginning and the end of the target sequence, sets pregex to &re, sets flags to f,[..]
There are two issues with this description:
Proposed resolution:
In 28.12.1.1 [re.regiter.cnstr]/2 change the above quoted part by
Effects: Initializes begin and end to point to the beginning and the end of the target sequence designated by the iterator range [a, b), sets pregex to &re, sets flags to
fm, then calls regex_search(begin, end, match, *pregex, flags). If this call returns false the constructor sets *this to the end-of-sequence iterator.
Section: 28.12.2.1 [re.tokiter.cnstr] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-03-03
View all other issues in [re.tokiter.cnstr].
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Discussion:
In 28.12.2.1 [re.tokiter.cnstr]/1+2 both the constructor declaration and the following text shows some obvious typos:
1) The third constructor form is written as
template <std::size_t N>
regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
const regex_type& re,
const int (&submatches)[R],
regex_constants::match_flag_type m =
regex_constants::match_default);
where the dimensions of submatches are specified by an unknown value R, which should be N.
2) Paragraph 2 of the same section says in its last sentence:
The third constructor initializes the member subs to hold a copy of the sequence of integer values pointed to by the iterator range [&submatches, &submatches + R).
where again R must be replaced by N.
3) Paragraph 3 of the same section says in its first sentence:
Each constructor then sets N to 0, and position to position_iterator(a, b, re, f).
where a non-existing parameter "f" is mentioned, which must be replaced by the parameter "m".
Proposed resolution:
Change 28.12.2.1 [re.tokiter.cnstr]/1:
template <std::size_t N>
regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
const regex_type& re,
const int (&submatches)[R N],
regex_constants::match_flag_type m =
regex_constants::match_default);
Change 28.12.2.1 [re.tokiter.cnstr]/2:
Effects: The first constructor initializes the member subs to hold the single value submatch. The second constructor initializes the member subs to hold a copy of the argument submatches. The third constructor initializes the member subs to hold a copy of the sequence of integer values pointed to by the iterator range [&submatches, &submatches +
RN).
Change 28.12.2.1 [re.tokiter.cnstr]/3:
Each constructor then sets N to 0, and position to position_iterator(a, b, re,
fm). If position is not an end-of-sequence iterator the constructor sets result to the address of the current match. Otherwise if any of the values stored in subs is equal to -1 the constructor sets *this to a suffix iterator that points to the range [a, b), otherwise the constructor sets *this to an end-of-sequence iterator.
Section: 1.2 [intro.refs] Status: NAD Submitter: Alisdair Meredith Date: 2007-03-08
View all other issues in [intro.refs].
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Discussion:
1.2 [intro.refs] Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this Interna- tional Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
- Ecma International, ECMAScript Language Specification, Standard Ecma-262, third edition, 1999.
- ISO/IEC 2382 (all parts), Information technology - Vocabulary
- ISO/IEC 9899:1990, Programming languages - C
- ISO/IEC 9899/Amd.1:1995, Programming languages - C, AMENDMENT 1: C Integrity
- ISO/IEC 9899:1999, Programming languages - C
- ISO/IEC 9899:1999/Cor.1:2001 Programming languages - C
- ISO/IEC 9899:1999/Cor.2:2004 Programming languages - C
- ISO/IEC 9945:2003, Information Technology-Portable Operating System Interface (POSIX)
- ISO/IEC 10646-1:1993 Information technology - Universal Multiple-Octet Coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual Plane
I'm not sure how many of those reserve naming patterns that might affect us, but I am equally sure I don't own a copy of any of these to check!
The point is to list the reserved naming patterns, rather than the individual names themselves - although we may want to list C keywords that are valid identifiers in C++ but likely to cause trouble in shared headers (e.g. restrict)
[ Kona (2007): Recommend NAD. No one has identified a specific defect, just the possibility of one. ]
[
Post-Kona: Alisdair request Open. A good example of the problem was a
discussion of the system error proposal, where it was pointed out an all-caps
identifier starting with a capital E conflicted with reserved macro names for
both Posix and C. I had absolutely no idea of this rule, and suspect I was
not the only one in the room.
Resolution will require someone with access to all the listed documents to
research their respective name reservation rules, or people with access to
specific documents add their rules to this issue until the list is complete.
]
[ Bellevue: Wording is aleady present in various standards, and no-one has come forward with wording. Suggest a formal paper rather than a defect report is the correct way to proceed. ]
Proposed resolution:
Section: 26.4.2 [rand.synopsis] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-03-08
View all other issues in [rand.synopsis].
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Discussion:
26.4.2 [rand.synopsis] the header <random> synopsis contains an unreasonable closing curly brace inside the subtract_with_carry_engine declaration.
Proposed resolution:
Change the current declaration in 26.4.2 [rand.synopsis]
template <class UIntType, size_t w}, size_t s, size_t r> class subtract_with_carry_engine;
[ Pete: Recommends editorial. ]
Section: 17.4.2.1 [using.headers] Status: NAD Submitter: Gennaro Prota Date: 2007-03-14
View all issues with NAD status.
Discussion:
17.4.2.1 [using.headers] states:
A translation unit shall include a header only outside of any external declaration or definition, [...]
I see three problems with this requirement:
The C++ standard doesn't define what an "external declaration" or an "external definition" are (incidentally the C99 standard does, and has a sentence very similar to the above regarding header inclusion).
I think the intent is that the #include directive shall lexically appear outside *any* declaration; instead, when the issue was pointed out on comp.std.c++ at least one poster interpreted "external declaration" as "declaration of an identifier with external linkage". If this were the correct interpretation, then the two inclusions below would be legal:
// at global scope
static void f()
{
# include <cstddef>
}
static void g()
{
# include <stddef.h>
}
(note that while the first example is unlikely to compile correctly, the second one may well do)
as the sentence stands, violations will require a diagnostic; is this the intent? It was pointed out on comp.std.c++ (by several posters) that at least one way to ensure a diagnostic exists:
[If there is an actual file for each header,] one simple way to implement this would be to insert a reserved identifier such as __begin_header at the start of each standard header. This reserved identifier would be ignored for all other purposes, except that, at the appropriate point in phase 7, if it is found inside an external definition, a diagnostic is generated. There's many other similar ways to achieve the same effect.
--James Kuyper, on comp.std.c++
is the term "header" meant to be limited to standard headers? Clause 17 is all about the library, but still the general question is interesting and affects one of the points in the explicit namespaces proposal (n1691):
Those seeking to conveniently enable argument-dependent lookups for all operators within an explicit namespace could easily create a header file that does so:
namespace mymath:: { #include "using_ops.hpp" }
Proposed resolution:
Rationale:
We believe that the existing language does not cause any real confusion and any new formulation of the rules that we could come up with are unlikely to be better than what's already in the standard.Section: 20.6 [function.objects] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-03-19
View all other issues in [function.objects].
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Discussion:
The header <functional> synopsis in 20.6 [function.objects] contains the following two free comparison operator templates for the function class template
template<class Function1, class Function2> void operator==(const function<Function1>&, const function<Function2>&); template<class Function1, class Function2> void operator!=(const function<Function1>&, const function<Function2>&);
which are nowhere described. I assume that they are relicts before the corresponding two private and undefined member templates in the function template (see 20.6.15.2 [func.wrap.func] and X [func.wrap.func.undef]) have been introduced. The original free function templates should be removed, because using an undefined entity would lead to an ODR violation of the user.
Proposed resolution:
Remove the above mentioned two function templates from the header <functional> synopsis (20.6 [function.objects])
template<class Function1, class Function2> void operator==(const function<Function1>&, const function<Function2>&); template<class Function1, class Function2> void operator!=(const function<Function1>&, const function<Function2>&);
Rationale:
Fixed by N2292 Standard Library Applications for Deleted Functions.Section: 22.2.2.1.2 [facet.num.get.virtuals] Status: NAD Submitter: Cosmin Truta Date: 2007-04-05
View other active issues in [facet.num.get.virtuals].
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Discussion:
From Section 22.2.2.1.2 [facet.num.get.virtuals], paragraphs 11 and 12, it is implied
that the value read from a stream must be stored
even if the placement of thousands separators does not conform to the
grouping() specification from the numpunct facet.
Since incorrectly-placed thousands separators are flagged as an extraction
failure (by the means of failbit), we believe it is better not
to store the value. A consistent strategy, in which any kind of extraction
failure leaves the input item intact, is conceptually cleaner, is able to avoid
corner-case traps, and is also more understandable from the programmer's point
of view.
Here is a quote from "The C++ Programming Language (Special Edition)" by B. Stroustrup (Section D.4.2.3, pg. 897):
"If a value of the desired type could not be read, failbit is set in r. [...] An input operator will use r to determine how to set the state of its stream. If no error was encountered, the value read is assigned through v; otherwise, v is left unchanged."
This statement implies that rdstate() alone is sufficient to
determine whether an extracted value is to be assigned to the input item
val passed to do_get. However, this is in disagreement
with the current C++ Standard. The above-mentioned assumption is true in all
cases, except when there are mismatches in digit grouping. In the latter case,
the parsed value is assigned to val, and, at the same time, err
is assigned to ios_base::failbit (essentially "lying" about the
success of the operation). Is this intentional? The current behavior raises
both consistency and usability concerns.
Although digit grouping is outside the scope of scanf (on which
the virtual methods of num_get are based), handling of grouping
should be consistent with the overall behavior of scanf. The specification of
scanf makes a distinction between input failures and matching
failures, and yet both kinds of failures have no effect on the input items
passed to scanf. A mismatch in digit grouping logically falls in
the category of matching failures, and it would be more consistent, and less
surprising to the user, to leave the input item intact whenever a failure is
being signaled.
The extraction of bool is another example outside the scope of
scanf, and yet consistent, even in the event of a successful
extraction of a long but a failed conversion from
long to bool.
Inconsistency is further aggravated by the fact that, when failbit is set,
subsequent extraction operations are no-ops until failbit is
explicitly cleared. Assuming that there is no explicit handling of
rdstate() (as in cin>>i>>j) it is
counter-intuitive to be able to extract an integer with mismatched digit
grouping, but to be unable to extract another, properly-formatted integer
that immediately follows.
Moreover, setting failbit, and selectively assigning a value to
the input item, raises usability problems. Either the strategy of
scanf (when there is no extracted value in case of failure), or
the strategy of the strtol family (when there is always an
extracted value, and there are well-defined defaults in case of a failure) are
easy to understand and easy to use. On the other hand, if failbit
alone cannot consistently make a difference between a failed extraction, and a
successful but not-quite-correct extraction whose output happens to be the same
as the previous value, the programmer must resort to implementation tricks.
Consider the following example:
int i = old_i;
cin >> i;
if (cin.fail())
// can the value of i be trusted?
// what does it mean if i == old_i?
// ...
Last but not least, the current behvaior is not only confusing to the casual
reader, but it has also been confusing to some book authors. Besides
Stroustrup's book, other books (e.g. "Standard C++ IOStreams and Locales" by
Langer and Kreft) are describing the same mistaken assumption. Although books
are not to be used instead of the standard reference, the readers of these
books, as well as the people who are generally familiar to scanf,
are even more likely to misinterpret the standard, and expect the input items
to remain intact when a failure occurs.
Proposed resolution:
Change 22.2.2.1.2 [facet.num.get.virtuals]:
Stage 3: The result of stage 2 processing can be one of
- A sequence of
charshas been accumulated in stage 2 that is converted (according to the rules ofscanf) to a value of the type ofval.This value is stored invalandios_base::goodbitis stored inerr.- The sequence of
charsaccumulated in stage 2 would have causedscanfto report an input failure.ios_base::failbitis assigned toerr.In the first case,
Ddigit grouping is checked. That is, the positions of discarded separators is examined for consistency withuse_facet<numpunct<charT> >(loc).grouping(). If they are not consistent thenios_base::failbitis assigned toerr. Otherwise, the value that was converted in stage 2 is stored invalandios_base::goodbitis stored inerr.
Rationale:
post-Toronto: Changed from New to NAD at the request of the author. The preferred solution of N2327 makes this resolution obsolete.Section: 17.3.1.3 [structure.specifications] Status: NAD Submitter: Thomas Plum Date: 2007-04-16
View all other issues in [structure.specifications].
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Discussion:
17.3.1.3 [structure.specifications] para 5 says
-5- Complexity requirements specified in the library clauses are upper bounds, and implementations that provide better complexity guarantees satisfy the requirements.
The following objection has been raised:
The library clauses suggest general guidelines regarding complexity, but we have been unable to discover any absolute hard-and-fast formulae for these requirements. Unless or until the Library group standardizes specific hard-and-fast formulae, we regard all the complexity requirements as subject to a "fudge factor" without any intrinsic upper bound.
[Plum ref _23213Y31 etc]
Proposed resolution:
Rationale:
Kona (2007): No specific instances of underspecification have been identified, and big-O notation always involves constant factors.Section: 28.12.2 [re.tokiter] Status: Pending NAD Editorial Submitter: Eric Niebler Date: 2007-06-02
View all other issues in [re.tokiter].
View all issues with Pending NAD Editorial status.
Discussion:
28.12.2 [re.tokiter], p3 says:
After it is constructed, the iterator finds and stores a value match_results<BidirectionalIterator> position and sets the internal count N to zero.
Should read:
After it is constructed, the iterator finds and stores a value
match_resultsregex_iterator<BidirectionalIterator, charT, traits> position and sets the internal count N to zero.
[ John adds: ]
Yep, looks like a typo/administrative fix to me.
Proposed resolution:
Section: 28.10 [re.results] Status: NAD Editorial Submitter: Nozomu Katoo Date: 2007-05-27
View all other issues in [re.results].
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Discussion:
In 28.4 [re.syn] of N2284, two template functions are declared here:
// 28.10, class template match_results:
<snip>
// match_results comparisons
template <class BidirectionalIterator, class Allocator>
bool operator== (const match_results<BidirectionalIterator, Allocator>& m1,
const match_results<BidirectionalIterator, Allocator>& m2);
template <class BidirectionalIterator, class Allocator>
bool operator!= (const match_results<BidirectionalIterator, Allocator>& m1,
const match_results<BidirectionalIterator, Allocator>& m2);
// 28.10.6, match_results swap:
But the details of these two bool operator functions (i.e., which members of match_results should be used in comparison) are not described in any following sections.
[ John adds: ]
That looks like a bug: operator== should return true only if the two objects refer to the same match - ie if one object was constructed as a copy of the other.
[ Kona (2007): Bill and Pete to add minor wording to that proposed in N2409. ]
Proposed resolution:
Add a new section after 28.10.6 [re.results.swap], which reads:
28.10.7 match_results non-member functions.
template<class BidirectionalIterator, class Allocator> bool operator==(const match_results<BidirectionalIterator, Allocator>& m1, const match_results<BidirectionalIterator, Allocator>& m2);Returns: true only if the two objects refer to the same match.
template<class BidirectionalIterator, class Allocator> bool operator!=(const match_results<BidirectionalIterator, Allocator>& m1, const match_results<BidirectionalIterator, Allocator>& m2);Returns: !(m1 == m2).
template<class BidirectionalIterator, class Allocator> void swap(match_results<BidirectionalIterator, Allocator>& m1, match_results<BidirectionalIterator, Allocator>& m2);Returns: m1.swap(m2).
[ Bellevue: Proposed wording now in WP. ]
Section: 20.7.11.2.4 [unique.ptr.single.observers], 20.7.12.2.5 [util.smartptr.shared.obs] Status: NAD Submitter: Beman Dawes Date: 2007-06-14
View all issues with NAD status.
Discussion:
The standard library uses the operator unspecified-bool-type() const idiom in five places. In three of those places (20.6.15.2.3 [func.wrap.func.cap], function capacity for example) the returned value is constrained to disallow unintended conversions to int. The standardese is
The return type shall not be convertible to int.
This constraint is omitted for unique_ptr and shared_ptr. It should be added for those.
[ Bellevue: ]
Close as NAD. Accepting paper N2435 makes it irrelevant.
Proposed resolution:
To the Returns paragraph for operator unspecified-bool-type() const of 20.7.11.2.4 [unique.ptr.single.observers] paragraph 11 and 20.7.12.2.5 [util.smartptr.shared.obs] paragraph 16, add the sentence:
The return type shall not be convertible to int.
[ Kona (2007): Uncertain if nullptr will address this issue. ]
Section: 26.7 [c.math] Status: NAD Editorial Submitter: Niels Dekker Date: 2007-06-10
View all other issues in [c.math].
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Discussion:
Quoting the latest draft (n2135), 26.7 [c.math]:
The added signatures are:
long abs(long); // labs() long abs(long long); // llabs()
Shouldn't abs(long long) have long long as return type?
Proposed resolution:
Change 26.7 [c.math]:
long long abs(long long); // llabs()
Rationale:
Had already been fixed in the WP by the time the LWG reviewed this.Section: 19.4 [syserr] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-06-24
View other active issues in [syserr].
View all other issues in [syserr].
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Discussion:
The most recent state of N2241 as well as the current draft N2284 (section 19.4 [syserr], p.2) proposes a new enumeration type posix_errno immediatly in the namespace std. One of the enumerators has the name invalid_argument, or fully qualified: std::invalid_argument. This name clashes with the exception type std::invalid_argument, see 19.1 [std.exceptions]/p.3. This clash makes e.g. the following snippet invalid:
#include <system_error>
#include <stdexcept>
void foo() { throw std::invalid_argument("Don't call us - we call you!"); }
I propose that this enumeration type (and probably the remaining parts of <system_error> as well) should be moved into one additional inner namespace, e.g. sys or system to reduce foreseeable future clashes due to the great number of members that std::posix_errno already contains (Btw.: Why has the already proposed std::sys sub-namespace from N2066 been rejected?). A further clash candidate seems to be std::protocol_error (a reasonable name for an exception related to a std network library, I guess).
Another possible resolution would rely on the proposed strongly typed enums, as described in N2213. But maybe the forbidden implicit conversion to integral types would make these enumerators less attractive in this special case?
Proposed resolution:
Fixed by issue 7 of N2422.
Section: 18.7.5 [propagation] Status: NAD Submitter: Jens Maurer Date: 2007-07-20
View other active issues in [propagation].
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Discussion:
From the Toronto Core wiki:
What do you mean by "null pointer constant"? How do you guarantee that exception_ptr() == 1 doesn't work? Do you even want to prevent that? What's the semantics? What about void *p = 0; exception_ptr() == p? Maybe disallow those in the interface, but how do you do that with portable C++? Could specify just "make it work".
Peter's response:
null pointer constant as defined in 4.10 [conv.ptr]. Intent is "just make it work", can be implemented as assignment operator taking a unique pointer to member, as in the unspecified bool type idiom.
[ Bellevue: ]
Original implementation was possible using the "unspecified-null-pointer" idiom, similar to unspecified-bool.
Even simpler now with nullptr_t.
NAD Rationale : null pointer constant is a perfectly defined term, and while API is clearly implementable there is no need to spell out implementation details.
Proposed resolution:
Section: 26.5.2.3 [valarray.access] Status: Pending NAD Editorial Submitter: Daniel Krügler Date: 2007-08-27
View all other issues in [valarray.access].
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Discussion:
Since the return type of valarray's operator[] const overload has been changed to const T& as described in 389 several paragraphs of the section 26.5.2.3 [valarray.access] are now incompletely specified, because many requirements and guarantees should now also apply to the const overload. Most notably, the address and reference guarantees should be extended to the const overload case.
Proposed resolution:
Change 26.5.2.3 [valarray.access]:
-1-
When applied to a constant array, the subscript operator returns a reference to the corresponding element of the array. When applied to a non-constant array, tThe subscript operator returns a reference to the corresponding element of the array.-3- The expression &a[i+j] == &a[i] + j evaluates as true for all size_t i and size_t j such that i+j is less than the length of the
non-constantarray a.-4- Likewise, the expression &a[i] != &b[j] evaluates as true for any two
non-constantarrays a and b and for any size_t i and size_t j such that i is less than the length of a and j is less than the length of b. This property indicates an absence of aliasing and may be used to advantage by optimizing compilers.281)-5- The reference returned by the subscript operator for an
non-constantarray is guaranteed to be valid until the member function resize(size_t, T) (26.5.2.7) is called for that array or until the lifetime of that array ends, whichever happens first.
Section: 23.1.3 [sequence.reqmts] Status: Pending NAD Editorial Submitter: David Abrahams Date: 2007-09-16
View all other issues in [sequence.reqmts].
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Discussion:
Table 90: (Optional sequence container operations) states the "assertion note pre/post-condition" of operator[] to be
*(a.begin() + n)
Surely that's meant to be "operational semantics?"
Proposed resolution:
Table 90: Optional sequence container operations expression return type assertion/note
pre/post-condition
operational semanticscontainer
Section: 26.4.1.3 [rand.req.eng] Status: NAD Submitter: Stephan Tolksdorf Date: 2007-09-21
View all other issues in [rand.req.eng].
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Discussion:
The 3rd table row in 26.4.1.3 [rand.req.eng]/3 requires random number engines to accept any arithmetic type as a seed, which is then casted to the engine's result_type and subsequently used for seeding the state of the engine. The requirement stated as "Creates an engine with initial state determined by static_cast<X::result_type>(s)" forces random number engines to either use a seeding method that completely depends on the result_type (see the discussion of seeding for the mersenne_twister_engine in point T2 above) or at least to throw away "bits of randomness" in the seed value if the result_type is smaller than the seed type. This seems to be inappropriate for many modern random number generators, in particular F2-linear or cryptographic ones, which operate on an internal bit array that in principle is independent of the type of numbers returned.
Posible resolution: I propose to change the wording to a version similar to "Creates an engine with initial state determined by static_cast<UintType>(s), where UintType is an implementation specific unsigned integer type."
Additionally, the definition of s in 26.4.1.3 [rand.req.eng]/1 c) could be restricted to unsigned integer types.
Similarly, the type of the seed in 26.4.1.4 [rand.req.adapt]/3 e) could be left unspecified.
See N2424 for further discussion.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In reply to the discussion in N2424 regarding this issue:
The descriptions of all engines and engine adaptors given in sections 26.4.3 [rand.eng] and 26.4.4 [rand.adapt] already specify the concrete types of the integer arguments for seeding. Hence, relaxing the general requirement in 26.4.1.3 [rand.req.eng] would not affect portability and reproducibility of the standard library. Furthermore, it is not clear to me what exactly the guarantee "with initial state determined by static_cast<X::result_type>(s)" is useful for. On the other hand, relaxing the requirement would allow developers to implement other random number engines that do not have to cast all arithmetic seed arguments to their result_types.
[ Bellevue: ]
Propose close NAD for the reasons given in N2424.
Proposed resolution:
See N2424 for further discussion.
[ Stephan Tolksdorf adds pre-Bellevue: ]
Change row 3 of table 105 "Random number engine requirements" in 26.4.1.3 [rand.req.eng]/3
Creates an engine with initial state determined bystatic_cast<X::result_type>(s)Similarly, change 26.4.1.4 [rand.req.adapt]/3 e)
When X::X is invoked withan X::result_typevalue s of arithmetic type (3.9.1), ...
Section: 26.4.1.4 [rand.req.adapt] Status: NAD Submitter: Stephan Tolksdorf Date: 2007-09-21
View all issues with NAD status.
Discussion:
If an engine adaptor is invoked with an argument of type seed_seq, then all base engines are specified to be seeded with this seed_seq. As seed_seq's randomization method is qualified as constant, this procedure will ef fectively initialize all base engines with the same seed (though the resulting state might still dif fer to a certain degree if the engines are of different types). It is not clear whether this mode of operation is in general appropriate, hence -- as far as the stated requirements are of general nature and not just specific to the engine adaptors provided by the library -- it might be better to leave the behaviour unspecified, since the current definition of seed_seq does not allow for a generally satisfying specification.
Posssible resolution: [As above]
See N2424 for further discussion.
[ Bellevue: ]
Close NAD for the reasons given in N2424.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 26.4.7.1 [rand.util.seedseq] Status: NAD Submitter: Stephan Tolksdorf Date: 2007-09-21
View other active issues in [rand.util.seedseq].
View all other issues in [rand.util.seedseq].
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Discussion:
The proper way to seed random number engines seems to be the most frequently discussed issue of the 26.4 [rand] proposal. While the new seed_seq approach is already rather general and probably sufficient for most situations, it is unlikely to be optimal in every case (one problem was pointed out in point T5 above). In some situations it might, for instance, be better to seed the state with a cryptographic generator.
In my opinion this is a pretty strong argument for extending the standard with a simple facility to customize the seeding procedure. This could, for example, be done with the following minimal changes:
Possible resolution:
Supplement the seed_seq with a traits class
template <typename T>
struct is_seed_seq { static const bool value = false; }
and the specialization
template <>
struct is_seed_seq<seed_seq> { static const bool value = true; }
which users can supplement with further specializations.
[ Bellevue: ]
See N2424. Close NAD but note that "conceptizing" the library may cause this problem to be solved by that route.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 26.4.1.5 [rand.req.dist] Status: NAD Submitter: Stephan Tolksdorf Date: 2007-09-21
View all issues with NAD status.
Discussion:
The requirement "P shall have a declaration of the form typedef X distribution_- type" effectively makes the use of inheritance for implementing distributions very inconvenient, because the child of a distribution class in general will not satisfy this requirement. In my opinion the benefits of having a typedef in the parameter class pointing back to the distribution class are not worth the hassle this requirement causes. [In my code base I never made use of the nested typedef but on several occasions could have profited from being able to use simple inheritance for the implementation of a distribution class.]
Proposed resolution: I propose to drop this requirement.
[ Bellevue: ]
Close NAD for the reasons given in N2424. In practice it is not inconvenient to meet these requirements.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 26.4.8.2.2 [rand.dist.bern.bin], 26.4.8.2.4 [rand.dist.bern.negbin] Status: NAD Submitter: Stephan Tolksdorf Date: 2007-09-21
View all issues with NAD status.
Discussion:
In my opinion the choice of name for the t parameter of the binomial_distribution is very unfortunate. In virtually every internet reference, book and software implementation this parameter is called n instead, see for example Wikipedia, Mathworld, Evans et al. (1993) Statistical Distributions, 2nd E., Wiley, p. 38, the R statistical computing language, p. 926, Mathematica and Matlab.
Similarly, the choice of k for the parameter of the negative binomial distributions is rather unusual. The most common choice for the negative binomial distribution seems to be r instead.
Choosing unusual names for the parameters causes confusion among users and makes the interface unnecessarily inconvenient to use.
Possible resolution: For these reasons, I propose to change the name of the respective parameters to n and r.
[ Bellevue: ]
In N2424. NAD It has been around for a while. It is hardly universal, there is prior art, and this would confuse people.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 26.4.8.5.1 [rand.dist.samp.discrete] Status: NAD Submitter: Stephan Tolksdorf Date: 2007-09-21
View other active issues in [rand.dist.samp.discrete].
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Discussion:
Possible resolution: I propose to change the specification such that the non-standardized probabilities need to be returned and that an additional requirement is included for the number of probabilities to be smaller than the maximum of IntType.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In reply to the discussion in N2424 of this issue:
Rescaled floating-point parameter vectors can not be expected to compare equal because of the limited precision of floating-point numbers. My proposal would at least guarantee that a parameter vector (of type double) passed into the distribution would compare equal with the one returned by the probabilities() method. Furthermore, I do not understand why "the changed requirement would lead to a significant increase in the amount of state in the distribution object". A typical implementation's state would increase by exactly one number: the sum of all probabilities. The textual representation for serialization would not need to grow at all. Finally, the proposed replacement "0 < n <= numeric_limits<IntType>::max() + 1" makes the implementation unnecessarily complicated, "0 < n <= numeric_limits<IntType>::max()" would be better.
[ Bellevue: ]
In N2424. We agree with the observation and the proposed resolution to part b). We recommend the wording n > 0 be replaced with 0 < n numeric_limits::max() + 1. However, we disagree with part a), as it would interfere with the definition of parameters' equality. Further, the changed requirement would lead to a significant increase in the amount of state of the distribution object.
As it stands now, it is convenient, and the changes proposed make it much less so.
NAD. Part a the current behavior is desirable. Part b, any constructor can fail, but the rules under which it can fail do not need to be listed here.
Proposed resolution:
See N2424 for the proposed resolution.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In 26.4.8.5.1 [rand.dist.samp.discrete]:
Proposed wording a):
Changae in para. 2
Constructs a discrete_distribution object with n=1 and p0 = w0 = 1and change in para. 5
Returns: A vector<double> whose size member returns n and whose operator[] member returnspkthe weight wk as a double value when invoked with argument k for k = 0, ..., n-1Proposed wording b):
Change in para. 3:
If firstW == lastW, let the sequence w have length n = 1 and consist of the single value w0 = 1. Otherwise, [firstW,lastW) shall form a sequence w of length n> 0such that 0 < n <= numeric_limits<IntType>::max(), and *firstW shall yield a value w0 convertible to double. [Note: The values wk are commonly known as the weights . -- end note]
Section: 26.4.8.5.2 [rand.dist.samp.pconst] Status: NAD Submitter: Stephan Tolksdorf Date: 2007-09-21
View other active issues in [rand.dist.samp.pconst].
View all other issues in [rand.dist.samp.pconst].
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Discussion:
The design of the constructor
template <class InputIteratorB, class InputIteratorW>
piecewise_constant_distribution( InputIteratorB firstB, InputIteratorB lastB,
InputIteratorW firstW);
is unnecessarily unsafe, as there is no separate end-iterator given for the weights. I can't see any performance or convenience reasons that would justify the risks inherent in such a function interface, in particular the risk that input error might go unnoticed.
Possible resolution: I propose to add an InputIteratorW lastW argument to the interface.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In reply to the discussion in N2424 I'd like to make the same comments as for 736.
[ Bellevue: ]
In N2424. There is already precedent elsewhere in the library. Follows existing convention. NAD.
Proposed resolution:
See N2424 for the proposed resolution.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In 26.4.8.5.2 [rand.dist.samp.pconst]:
Proposed wording a)
Change in para. 2
Constructs a piecewise_constant_distribution object with n = 1, p0 = w0 = 1, b0 = 0, and b1 = 1and change in para. 5
A vector<result_type> whose size member returns n and whose operator[] member returnspkthe weight wk as a double value when invoked with argument k for k = 0, ..., n-1Proposed wording b)
Change both occurrences of
"piecewise_constant_distribution(InputIteratorB firstB, InputIteratorB lastB, InputIteratorW firstW, InputIteratorW lastW)and change in para. 3
the length of the sequence w starting from firstW shall be at least n, *firstW shall return a value w0 that is convertible to double, and any wk for k >= n shall be ignored by the distribution[firstW, lastW) shall form a sequence w of length n whose leading element w0 shall be convertible to double
Section: 26.4.4.1 [rand.adapt.disc] Status: Pending NAD Editorial Submitter: Stephan Tolksdorf Date: 2007-09-21
View all issues with Pending NAD Editorial status.
Discussion:
Since the template parameter p and r are of type size_t, the member n in the class exposition should have type size_t, too.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 26.4.7.2 [rand.util.canonical] Status: NAD Submitter: Stephan Tolksdorf Date: 2007-09-21
View all other issues in [rand.util.canonical].
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Discussion:
The complexity of generate_canonical is specified to be "exactly k=max(1, ceil(b/log2 R)) invocations of g". This terms involves a logarithm that is not rounded and hence can not (in general) be computed at compile time. As this function template is performance critical, I propose to replace ceil(b/log2 R) with ceil(b/floor(log2 R)).
See N2424 for further discussion.
[ Bellevue: ]
In N2424. Close NAD as described there.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 20.7.12.2.11 [util.smartptr.getdeleter] Status: NAD Submitter: Daniel Krügler Date: 2007-09-27
View all other issues in [util.smartptr.getdeleter].
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Discussion:
The following issue was raised by Alf P. Steinbach in c.l.c++.mod:
According to the recent draft N2369, both the header memory synopsis of 20.7 [memory] and 20.7.12.2.11 [util.smartptr.getdeleter] declare:
template<class D, class T> D* get_deleter(shared_ptr<T> const& p);
This allows to retrieve the pointer to a mutable deleter of a const shared_ptr (if that owns one) and therefore contradicts the usual philosophy that associated functors are either read-only (e.g. key_comp or value_comp of std::map) or do at least reflect the mutability of the owner (as seen for the both overloads of unique_ptr::get_deleter). Even the next similar counter-part of get_deleter - the two overloads of function::target in the class template function synopsis 20.6.15.2 [func.wrap.func] or in 20.6.15.2.5 [func.wrap.func.targ] - do properly mirror the const-state of the owner.
Possible proposed resolutions:Replace the declarations of get_deleter in the header <memory> synopsis of 20.7 [memory] and in 20.7.12.2.11 [util.smartptr.getdeleter] by one of the following alternatives (A) or (B):
template<class D, class T> const D* get_deleter(shared_ptr<T> const& p);
Alberto Ganesh Barbati adds:
Replace it with two functions:
template <class D, class T> D get_deleter(shared_ptr<T> const&); template <class D, class T> bool has_deleter(shared_ptr<T> const&);
The first one would throw if D is the wrong type, while the latter would never throw. This approach would reflect the current praxis of use_facet/has_facet, with the twist of returning the deleter by value as container::get_allocator() do.
Peter Dimov adds:
My favorite option is "not a defect". A, B and C break useful code.
[ Bellevue: ]
Concern this is similar to confusing "pointer to const" with "a constant pointer".
Proposed resolution:
Section: 18.7.5 [propagation] Status: NAD Submitter: Alisdair Meredith Date: 2007-10-10
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Discussion:
It could be I did not understand the design rationale, but I thought copy_exception would produce an exception_ptr to the most-derived (dynamic) type of the passed exception. Instead it slices, which appears to be less useful, and a likely source of FAQ questions in the future.
(Peter Dimov suggests NAD)
[ Bellevue: ]
How could this be implemented in a way that the dynamic type is cloned?
The feature is designed to create an exception_ptr from an object whose static type is identical to the dynamic type and thus there is no slicing involved.
Proposed resolution:
Section: 20.5.4.3 [meta.unary.prop] Status: NAD Submitter: Alisdair Meredith Date: 2007-10-10
View all other issues in [meta.unary.prop].
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Discussion:
I am trying to decide is a pure virtual function is a necessary as well as sufficient requirement to be classified as abstract?
For instance, is the following (non-polymorphic) type considered abstract?
struct abstract {
protected:
abstract(){}
abstract( abstract const & ) {}
~abstract() {}
};
(Suggested that this may be NAD, with an editorial fix-up from Pete on the core wording to make clear that abstract requires a pure virtual function)
Proposed resolution:
Core has clarified that the definition abstract is adequate. Issue withdrawn by submitter. NAD.
Section: 20.7.10.1 [uninitialized.copy] Status: NAD Editorial Submitter: Daniel Krügler Date: 2007-10-15
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Discussion:
14882-2003, [lib.uninitialized.copy] is currently written as follows:
template <class InputIterator, class ForwardIterator> ForwardIterator uninitialized_copy(InputIterator first, InputIterator last, ForwardIterator result);-1- Effects:
for (; first != last; ++result, ++first) new (static_cast<void*>(&*result)) typename iterator_traits<ForwardIterator>::value_type(*first);-2- Returns: result
similarily for N2369, and its corresponding section 20.7.10.1 [uninitialized.copy].
It's not clear to me what the return clause is supposed to mean, I see two possible interpretations:
The problem is: I see nothing in the standard which grants that this interpretation is correct, specifically [lib.structure.specifications] or 17.3.1.3 [structure.specifications] resp. do not clarify which "look-up" rules apply for names found in the elements of the detailed specifications - Do they relate to the corresponding synopsis or to the effects clause (or possibly other elements)? Fortunately most detailed descriptions are unambigious in this regard, e.g. this problem does not apply for std::copy.
Proposed resolution:
Change the wording of the return clause to say (20.7.10.1 [uninitialized.copy]):
-2- Returns: The value of result after effects have taken place.
[ Bellevue: ]
Resolution: NAD editorial -- project editor to decide if change is worthwhile. Concern is that there are many other places this might occur.
Section: 23.2.5 [container.adaptors] Status: NAD Editorial Submitter: Paolo Carlini Date: 2007-10-31
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Discussion:
After n2369 we have a single push_back overload in the sequence containers, of the "emplace" type. At variance with that, still in n2461, we have two separate overloads, the C++03 one + one taking an rvalue reference in the container adaptors. Therefore, simply from a consistency point of view, I was wondering whether the container adaptors should be aligned with the specifications of the sequence container themselves: thus have a single push along the lines:
template<typename... _Args>
void
push(_Args&&... __args)
{ c.push_back(std::forward<_Args>(__args)...); }
[ Related to 767 ]
Proposed resolution:
Change 23.2.5.1.1 [queue.defn]:
void push(const value_type& x) { c.push_back(x); }void push(value_type&& x) { c.push_back(std::move(x)); }template<class... Args> void push(Args&&... args) { c.push_back(std::forward<Args>(args)...); }
Change 23.2.5.2 [priority.queue]:
void push(const value_type& x) { c.push_back(x); }void push(value_type&& x) { c.push_back(std::move(x)); }template<class... Args> void push(Args&&... args) { c.push_back(std::forward<Args>(args)...); }
Change 23.2.5.2.2 [priqueue.members]:
void push(const value_type& x);
Effects:c.push_back(x);push_heap(c.begin(), c.end(), comp);template<class... Args> void push(value_typeArgs&&...xargs);Effects:
c.push_back(std::moveforward<Args>(xargs)...); push_heap(c.begin(), c.end(), comp);
Change 23.2.5.3.1 [stack.defn]:
void push(const value_type& x) { c.push_back(x); }void push(value_type&& x) { c.push_back(std::move(x)); }template<class... Args> void push(Args&&... args) { c.push_back(std::forward<Args>(args)...); }
Rationale:
Addressed by N2680 Proposed Wording for Placement Insert (Revision 1).
Section: 23.2.6 [vector] Status: NAD Editorial Submitter: Paolo Carlini Date: 2007-11-04
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Discussion:
In the synopsis 23.2.6 [vector], there is the signature:
void insert(const_iterator position, size_type n, T&& x);
instead of:
iterator insert(const_iterator position, T&& x);
23.2.6.4 [vector.modifiers] is fine.
Proposed resolution:
Change the synopsis in 23.2.6 [vector]:
iterator insert(const_iterator position, const T& x); iterator insert(const_iterator position, T&& x); void insert(const_iterator position, size_type n, const T& x);void insert(const_iterator position, size_type n, T&& x);
Section: 23.1.4 [associative.reqmts] Status: NAD Submitter: Sylvain Pion Date: 2007-12-04
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Discussion:
The associative containers provide 2 overloads of emplace():
template <class... Args> pair<iterator, bool> emplace(Args&&... args); template <class... Args> iterator emplace(const_iterator position, Args&&... args);
This is a problem if you mean the first overload while passing a const_iterator as first argument.
[ Related to 767 ]
[ Bellevue: ]
This can be disambiguated by passing "begin" as the first argument in the case when the non-default choice is desired. We believe that desire will be rare.
Resolution: Change state to NAD.
Proposed resolution:
Rename one of the two overloads. For example to emplace_here, hint_emplace...
Section: 23.1.5 [unord.req] Status: NAD Submitter: Joe Gottman Date: 2007-11-29
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Discussion:
A major attribute of the unordered containers is that iterating though them inside a bucket is very fast while iterating between buckets can be much slower. If an unordered container has a low load factor, iterating between the last iterator in one bucket and the next iterator, which is in another bucket, is O(bucket_count()) which may be much larger than O(size()).
If b is an non-const unordered container of type B and k is an object of it's key_type, then b.equal_range(k) currently returns pair<B::iterator, B::iterator>. Consider the following code:
B::iterator lb, ub;
tie(lb, ub) = b.equal_range(k);
for (B::iterator it = lb; it != ub; ++it) {
// Do something with *it
}
If b.equal_range(k) returns a non-empty range (i.e. b contains at least on element whose key is equivalent to k), then every iterator in the half-open range [lb, ub) will be in the same bucket, but ub will likely either be in a different bucket or be equal to b.end(). In either case, iterating between ub - 1 and ub could take a much longer time than iterating through the rest of the range.
If instead of returning pair<iterator, iterator>, equal_range were to return pair<local_iterator, local_iterator>, then ub (which, like lb, would now be a local_iterator) could be guaranteed to always be in the same bucket as lb. In the cases where currently ub is equal to b.end() or is in a different bucket, ub would be equal to b.end(b.bucket(key)). This would make iterating between lb and ub much faster, as every iteration would be constant time.
[ Bellevue: ]
The proposed resolution breaks consistency with other container types for dubious benefit, and iterators are already constant time.
Proposed resolution:
Change the entry for equal_range in Table 93 (23.1.5 [unord.req]) as follows:
| expression | return type | assertion/note pre/post-condition | complexity |
|---|---|---|---|
| b.equal_range(k) | pair<local_iterator,local_iterator>; pair<const_local_iterator,const_local_iterator> for const b. | Returns a range containing all elements with keys equivalent to k. Returns make_pair(b.end(b.bucket(key)),b.end(b.bucket(key))) if no such elements exist. | Average case Θ(b.count(k)). Worst case Θ(b.size()). |
Section: 23 [containers] Status: NAD Editorial Submitter: Sylvain Pion Date: 2007-12-28
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Discussion:
Playing with g++'s C++0X mode, I noticed that the following code, which used to compile:
#include <vector>
int main()
{
std::vector<char *> v;
v.push_back(0);
}
now fails with the following error message:
.../include/c++/4.3.0/ext/new_allocator.h: In member function 'void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, _Args&& ...) [with _Args = int, _Tp = char*]': .../include/c++/4.3.0/bits/stl_vector.h:707: instantiated from 'void std::vector<_Tp, _Alloc>::push_back(_Args&& ...) [with _Args = int, _Tp = char*, _Alloc = std::allocator<char*>]' test.cpp:6: instantiated from here .../include/c++/4.3.0/ext/new_allocator.h:114: error: invalid conversion from 'int' to 'char*'
As far as I know, g++ follows the current draft here.
Does the committee really intend to break compatibility for such cases?
[ Sylvain adds: ]
I just noticed that std::pair has the same issue. The following now fails with GCC's -std=c++0x mode:
#include <utility> int main() { std::pair<char *, char *> p (0,0); }I have not made any general audit for such problems elsewhere.
[ Related to 756 ]
[ Bellevue: ]
Motivation is to handle the old-style int-zero-valued NULL pointers. Problem: this solution requires concepts in some cases, which some users will be slow to adopt. Some discussion of alternatives involving prohibiting variadic forms and additional library-implementation complexity.
Discussion of "perfect world" solutions, the only such solution put forward being to retroactively prohibit use of the integer zero for a NULL pointer. This approach was deemed unacceptable given the large bodies of pre-existing code that do use integer zero for a NULL pointer.
Another approach is to change the member names. Yet another approach is to forbid the extension in absence of concepts.
Resolution: These issues (756, 767, 760, 763) will be subsumed into a paper to be produced by Alan Talbot in time for review at the 2008 meeting in France. Once this paper is produced, these issues will be moved to NAD.
Proposed resolution:
Add the following rows to Table 90 "Optional sequence container operations", 23.1.3 [sequence.reqmts]:
expression return type assertion/note
pre-/post-conditioncontainer a.push_front(t) void a.insert(a.begin(), t)
Requires: T shall be CopyConstructible.list, deque a.push_front(rv) void a.insert(a.begin(), rv)
Requires: T shall be MoveConstructible.list, deque a.push_back(t) void a.insert(a.end(), t)
Requires: T shall be CopyConstructible.list, deque, vector, basic_string a.push_back(rv) void a.insert(a.end(), rv)
Requires: T shall be MoveConstructible.list, deque, vector, basic_string
Change the synopsis in 23.2.2 [deque]:
void push_front(const T& x); void push_front(T&& x); void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change 23.2.2.3 [deque.modifiers]:
void push_front(const T& x); void push_front(T&& x); void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change the synopsis in 23.2.4 [list]:
void push_front(const T& x); void push_front(T&& x); void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change 23.2.4.3 [list.modifiers]:
void push_front(const T& x); void push_front(T&& x); void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change the synopsis in 23.2.6 [vector]:
void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change 23.2.6.4 [vector.modifiers]:
void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Rationale:
Addressed by N2680 Proposed Wording for Placement Insert (Revision 1).
If there is still an issue with pair, Howard should submit another issue.
Section: 26.4.8.1 [rand.dist.uni] Status: NAD Submitter: P.J. Plauger Date: 2008-01-14
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Discussion:
[ Bellevue: ]
NAD. Withdrawn.
Proposed resolution:
Section: 30.3.3.2.3 [thread.lock.unique.mod] Status: NAD Submitter: Constantine Sapuntzakis Date: 2008-02-02
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Discussion:
unique_lock::release will probably lead to many mistakes where people call release instead of unlock. I just coded such a mistake using the boost pre-1.35 threads library last week.
In many threading libraries, a call with release in it unlocks the lock (e.g. ReleaseMutex in Win32, java.util.concurrent.Semaphore).
I don't call unique_lock::lock much at all, so I don't get to see the symmetry between ::lock and ::unlock. I usually use the constructor to lock the mutex. So I'm left to remember whether to call release or unlock during the few times I need to release the mutex before the scope ends. If I get it wrong, the compiler doesn't warn me.
An alternative name for release may be disown.
This might be a rare case where usability is hurt by consistency with the rest of the C++ standard (e.g. std::auto_ptr::release).
[ Bellevue: ]
Change a name from release to disown. However prior art uses the release name. Compatibility with prior art is more important that any possible benefit such a change might make. We do not see the benefit for changing. NAD
Proposed resolution:
Change the synopsis in 30.3.3.2 [thread.lock.unique]:
template <class Mutex>
class unique_lock
{
public:
...
mutex_type* release disown();
...
};
Change 30.3.3.2.3 [thread.lock.unique.mod]:
mutex_type *releasedisown();
Section: X [datetime.system] Status: NAD Editorial Submitter: Christopher Kohlhoff, Jeff Garland Date: 2008-02-03
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Discussion:
The draft C++0x thread library requires that the time points of type system_time and returned by get_system_time() represent Coordinated Universal Time (UTC) (section X [datetime.system]). This can lead to surprising behavior when a library user performs a duration-based wait, such as condition_variable::timed_wait(). A complete explanation of the problem may be found in the Rationale for the Monotonic Clock section in POSIX, but in summary:
POSIX solves the problem by introducing a new monotonic clock, which is unaffected by changes to the system time. When a condition variable is initialized, the user may specify whether the monotonic clock is to be used. (It is worth noting that on POSIX systems it is not possible to use condition_variable::native_handle() to access this facility, since the desired clock type must be specified during construction of the condition variable object.)
In the context of the C++0x thread library, there are added dimensions to the problem due to the need to support platforms other than POSIX:
One possible minimal solution:
Proposed resolution:
Rationale:
Addressed by N2661: A Foundation to Sleep On.Section: 26.4.4.4 [rand.adapt.xor] Status: NAD Submitter: P.J. Plauger Date: 2008-02-09
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Discussion:
xor_combine::seed(result_type) and seed(seed_seq&) don't say what happens to each of the sub-engine seeds. (Should probably do the same to both, unlike TR1.)
[ Bellevue: ]
Overcome by the previous proposal. NAD mooted by resolution of 789.
Proposed resolution:
Section: 26.4.8.5.2 [rand.dist.samp.pconst] Status: NAD Submitter: P.J. Plauger Date: 2008-02-09
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Discussion:
piecewise_constant_distribution::densities() should be probabilities(), just like discrete_distribution. (There's no real use for weights divided by areas.)
[ Bellevue: ]
Fermilab does not agree with this summary. As defined in the equation in 26.4.8.5.2/4, the quantities are indeed probability densities not probabilities. Because we view this distribution as a parameterization of a *probability density function*, we prefer to work in terms of probability densities.
We don't think this should be changed.
If there is a technical argument about why the implementation dealing with these values can't be as efficient as one dealing with probabilities, we might reconsider. We don't care about this one member function being somewhat more or less efficient; we care about the size of the distribution object and the speed of the calls to generate variates.
Proposed resolution:
Change synopsis in 26.4.8.5.2 [rand.dist.samp.pconst]:
template <class RealType = double>
class piecewise_constant_distribution
{
public:
...
vector<double> densities probabilities() const;
...
};
Change 26.4.8.5.2 [rand.dist.samp.pconst]/6:
vector<double>densitiesprobabilities() const;
Section: 26.4.8.5.3 [rand.dist.samp.genpdf] Status: Dup Submitter: P.J. Plauger Date: 2008-02-09
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Duplicate of: 732
Discussion:
general_pdf_distribution should be dropped. (It's a research topic in adaptive numerical integration.)
[ Stephan Tolksdorf notes: ]
This appears to be a duplicate of 732.
Proposed resolution:
Section: 26.4.5 [rand.predef] Status: NAD Submitter: P.J. Plauger Date: 2008-02-09
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Discussion:
The 10,000th value returned by ranlux48_base is supposed to be 61839128582725. We get 192113843633948. (Note that the underlying generator was changed in Kona.)
[ Bellevue: ]
Submitter withdraws defect.
Proposed resolution:
Change 26.4.5 [rand.predef]/p5:
typedef subtract_with_carry_engine<uint_fast64_t, 48, 5, 12> ranlux48_base;Required behavior: The 10000th consecutive invocation of a default-constructed object of type ranlux48_base shall produce the value61839128582725192113843633948.
Section: 26.4.5 [rand.predef] Status: NAD Submitter: P.J. Plauger Date: 2008-02-09
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Discussion:
The 10,000th value returned by ranlux48 is supposed to be 249142670248501. We get 88229545517833. (Note that this depends on ranlux48_base.)
[ Bellevue: ]
Submitter withdraws defect.
Proposed resolution:
Change 26.4.5 [rand.predef]/p6:
typedef discard_block_engine<ranlux48_base, 389, 11> ranlux48Required behavior: The 10000th consecutive invocation of a default-constructed object of type ranlux48 shall produce the value24914267024850188229545517833.
Section: 26.4.3.2 [rand.eng.mers], TR1 5.1.4.2 [tr.rand.eng.mers] Status: NAD Submitter: Stephan Tolksdorf Date: 2008-02-18
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Discussion:
TR1 5.1.4.2 [tr.rand.eng.mers](10) requires that operator== for the mersenne_twister returns true if and only if the states of two mersenne_twisters, consisting each of n integers between 0 and 2w - 1, are completely equal. This is a contradiction with TR1 5.1.1 [tr.rand.req](3) because the given definition of the state also includes the lower r bits of x(i-n), which will never be used to generate a random number. If two mersenne_twisters only differ in the lower bits of x(i-n) they will not compare equal, although they will produce an identical sequence of random numbers.
26.4.3.2 [rand.eng.mers] in the latest C++ draft does not specify the behaviour of operator== but uses a similar definition of the state and, just like TR1 5.1.4.2 [tr.rand.eng.mers], requires the textual representation of a mersenne_twister_engine to consist of Xi-n to Xi-1, including the lower bits of Xi-n. This leads to two problems: First, the unsuspecting implementer is likely to erroneously compare the lower r bits of Xi-n in operator==. Second, if only the lower r bits differ, two mersenne_twister_engines will compare equal (if correctly implemented) but have different textual representations, which conceptually is a bit ugly.
I propose that a paragraph or footnote is added to 26.4.3.2 [rand.eng.mers] which clarifies that the lower r bits of Xi-n are not to be compared in operator== and operator!=. It would only be consequent if furthermore the specification for the textual respresentation was changed to Xi-n bitand ((2w - 1) - (2r - 1)), Xi-(n-1), ..., Xi-1 or something similar.
These changes would likely have no practical effect, but would allow an implementation that does the right thing to be standard-conformant.
[ Bellevue: ]
Fermi Lab has no objection to the proposed change. However it feels that more time is needed to check the details, which would suggest a change to REVIEW.
Bill feels that this is NAD, not enough practical importance to abandon the simple definition of equality, and someone would have to do a lot more study to ensure that all cases are covered for a very small payback. The submitter admits that "These changes would likely have no practical effect,", and according to Plum's razor this means that it is not worth the effort!
Revisted: Agree that the fact that there is no practical difference means that no change can be justified.
Proposed resolution:
In 26.4.3.2 [rand.eng.mers]:
Insert at the end of para 2.:
[Note: The lower r bits of Xi-n do not influence the state transition and hence should not be compared when comparing two mersenne_twister_engine objects. -- end note]In para 5. change:
The textual representation of xi consists of the values of Xi-n bitand ((2w - 1) - (2r - 1)), Xi-(n-1), ..., Xi-1, in that order.
Section: 26.4.5 [rand.predef] Status: NAD Submitter: P.J. Plauger Date: 2008-02-20
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Discussion:
The 10,000th value returned by knuth_b is supposed to be 1112339016. We get 2126698284.
Proposed resolution:
Change 26.4.5 [rand.predef]/p8:
typedef shuffle_order_engine<minstd_rand0, 256> knuth_b;Required behavior: The 10000th consecutive invocation of a default-constructed object of type knuth_b shall produce the value11123390162126698284.
[ Bellevue: Submitter withdraws defect. "We got the wrong value for entirely the right reasons". NAD. ]
Section: 22.2.2.2 [locale.nm.put] Status: NAD Submitter: Peter Dimov Date: 2008-04-07
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Discussion:
In the spirit of printf vs iostream...
POSIX printf says that %'d should insert grouping characters (and the implication is that in the absence of ' no grouping characters are inserted). The num_put facet, on the other hand, seems to always insert grouping characters. Can this be considered a defect worth fixing for C++0x? Maybe ios_base needs an additional flag?
[ Pablo Halpern: ]
I'm not sure it constitutes a defect, but I would be in favor of adding another flag (and corresponding manipulator).
[ Martin Sebor: ]
I don't know if it qualifies as a defect but I agree that there should be an easy way to control whether the thousands separator should or shouldn't be inserted. A new flag would be in line with the current design of iostreams (like boolalpha, showpos, or showbase).
[ Sophia Antipolis: ]
This is not a part of C99. LWG suggests submitting a paper may be appropriate.
Proposed resolution:
Section: 21.1.3 [char.traits.specializations] Status: NAD Editorial Submitter: Dietmar Kühl Date: 2008-04-23
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Discussion:
In Table 56 (Traits requirements) the not_eof() member function
is using an argument of type e which denotes an object of
type X::int_type. However, the specializations in
21.1.3 [char.traits.specializations] all use char_type.
This would effectively mean that the argument type actually can't
represent EOF in the first place. I'm pretty sure that the type used
to be int_type which is quite obviously the only sensible
argument.
This issue is close to being editorial. I suspect that the proposal
changing this section to include the specializations for char16_t
and char32_t accidentally used the wrong type.
Proposed resolution:
In 21.1.3.1 [char.traits.specializations.char],
21.1.3.2 [char.traits.specializations.char16_t],
21.1.3.3 [char.traits.specializations.char32_t], and
[char.traits.specializations.wchar_t] correct the
argument type from char_type to int_type.
Rationale:
Already fixed in WP.Section: 20.2.3 [pairs] Status: NAD Submitter: Thorsten Ottosen Date: 2008-05-23
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Discussion:
I have one issue with std::pair. Well, it might just be a very annoying historical accident, but why is there no default template argument for the second template argument? This is so annoying when the type in question is looong and hard to write (type deduction with auto won't help those cases where we use it as a return or argument type).
Proposed resolution:
Change the synopsis in 20.2 [utility] to read:
template <class T1, class T2 = T1> struct pair;
Change 20.2.3 [pairs] to read:
namespace std {
template <class T1, class T2 = T1>
struct pair {
typedef T1 first_type;
typedef T2 second_type;
...
Rationale:
std::pair is a heterogeneous container.