explanations.html: New file.
2001-07-09 Phil Edwards <pme@sources.redhat.com> * docs/html/explanations.html: New file. * docs/html/configopts.html: Link to it to provide more notes on cstdio. Minor markup and spacing fixes. * docs/html/27_io/howto.html: Talk about sync_with_stdio. From-SVN: r43868
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Phil Edwards
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2001-07-09 Phil Edwards <pme@sources.redhat.com>
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* docs/html/explanations.html: New file.
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* docs/html/configopts.html: Link to it to provide more notes
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on cstdio. Minor markup and spacing fixes.
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* docs/html/27_io/howto.html: Talk about sync_with_stdio.
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2001-07-09 Kriang Lerdsuwanakij <lerdsuwa@users.sourceforge.net>
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* include/bits/valarray_meta.h (_Expr::operator+): Use qualified id
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@ -8,7 +8,7 @@
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<META NAME="GENERATOR" CONTENT="vi and eight fingers">
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<TITLE>libstdc++-v3 HOWTO: Chapter 27</TITLE>
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<LINK REL=StyleSheet HREF="../lib3styles.css">
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<!-- $Id: howto.html,v 1.4 2001/04/03 00:26:56 pme Exp $ -->
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<!-- $Id: howto.html,v 1.5 2001/05/30 21:55:03 pme Exp $ -->
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</HEAD>
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<BODY>
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@ -29,6 +29,7 @@
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<LI><A HREF="#5">What is this <sstream>/stringstreams thing?</A>
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<LI><A HREF="#6">Deriving a stream buffer</A>
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<LI><A HREF="#7">More on binary I/O</A>
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<LI><A HREF="#8">Pathetic performance? Ditch C.</A>
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</UL>
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<HR>
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@ -400,14 +401,65 @@
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a portable binary format.
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</P>
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<HR>
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<H2><A NAME="8">Pathetic performance? Ditch C.</A></H2>
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<P>It sounds like a flame on C, but it isn't. Really. Calm down.
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I'm just saying it to get your attention.
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</P>
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<P>Because the C++ library includes the C library, both C-style and
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C++-style I/O have to work at the same time. For example:
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<PRE>
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#include <iostream>
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#include <cstdio>
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std::cout << "Hel";
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std::printf ("lo, worl");
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std::cout << "d!\n";
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</PRE>
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This must do what you think it does.
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</P>
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<P>Alert members of the audience will immediately notice that buffering
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is going to make a hash of the output unless special steps are taken.
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</P>
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<P>The special steps taken by libstdc++, at least for version 3.0,
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involve doing very little buffering for the standard streams, leaving
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most of the buffering to the underlying C library. (This kind of
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thing is <A HREF="../explanations.html#cstdio">tricky to get right</A>.)
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The upside is that correctness is insured. The downside is that
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writing through <TT>cout</TT> can quite easily lead to awful
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performance when the C++ I/O library is layered on top of the C I/O
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library (as it is for 3.0 by default). Some patches are in the
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works which should improve the situation for 3.1.
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</P>
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<P>However, the C and C++ standard streams only need to be kept in sync
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when both libraries' facilities are in use. If your program only uses
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C++ I/O, then there's no need to sync with the C streams. The right
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thing to do in this case is to call
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<PRE>
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#include <EM>any of the I/O headers such as ios, iostream, etc</EM>
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std::sync_with_stdio(false);
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</PRE>
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</P>
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<P>You must do this before performing any I/O via the C++ stream objects.
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Once you call this, the C++ streams will operate independantly of the
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(unused) C streams. For GCC 3.0, this means that <TT>cout</TT> and
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company will become fully buffered on their own.
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</P>
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<P>Note, by the way, that the synchronization requirement only applies to
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the standard streams (cin, cout, cerr, clog, and thier wide-character
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counterparts). File stream objects that you create yourself have no
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such requirement and are fully buffered.
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</P>
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<!-- ####################################################### -->
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<HR>
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<HR><BR><BR><BR><BR><BR><BR><BR><BR>
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<P CLASS="fineprint"><EM>
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Comments and suggestions are welcome, and may be sent to
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<A HREF="mailto:libstdc++@gcc.gnu.org">the mailing list</A>.
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<BR> $Id: howto.html,v 1.4 2001/04/03 00:26:56 pme Exp $
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<BR> $Id: howto.html,v 1.5 2001/05/30 21:55:03 pme Exp $
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</EM></P>
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@ -7,7 +7,7 @@
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<META NAME="GENERATOR" CONTENT="vi and eight fingers">
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<TITLE>libstdc++-v3 configure options</TITLE>
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<LINK REL=StyleSheet HREF="lib3styles.css">
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<!-- $Id: configopts.html,v 1.9 2001/04/06 01:47:11 bkoz Exp $ -->
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<!-- $Id: configopts.html,v 1.10 2001/04/20 08:59:25 bkoz Exp $ -->
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</HEAD>
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<BODY>
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@ -66,56 +66,55 @@ options</A></H1>
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I/O package (from
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<A HREF="http://sources.redhat.com/glibc/">glibc</A>, the
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GNU C library), or 'stdio' to use a generic "C"
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abstraction. The default is 'stdio'.
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abstraction. The default is 'stdio'. A longer explanation
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is <A HREF="explanations.html#cstdio">here</A>.
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</P>
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<DT><TT>--enable-sjlj-exceptions </TT>
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<DD><P> Forces old, short-jump/long-jump exception handling model. If
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at all possible, the new, frame unwinding exception handling routines
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should be used instead, as they significantly reduce both runtime
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memory usage and executable size.
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<DT><TT>--enable-sjlj-exceptions </TT>
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<DD><P>Forces old, short-jump/long-jump exception handling model. If
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at all possible, the new, frame unwinding exception handling routines
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should be used instead, as they significantly reduce both runtime
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memory usage and executable size.
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</P>
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<DT><TT>--enable-clocale </TT>
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<DD><P>This is an abbreviated form of <TT>'--enable-clocale=generic'</TT>
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(described next).
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</P>
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<DT><TT>--enable-clocale=MODEL </TT> <DD><P>Select a target-specific
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underlying locale package. The choices are 'gnu' to specify an X/Open
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(IEEE Std. 1003.1-200x) model based on langinfo/iconv (from <A
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HREF="http://sources.redhat.com/glibc/">glibc</A>, the GNU C
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library), or 'generic' to use a generic "C" abstraction
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which consists of "C" locale info. The default is
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'generic'.
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<DT><TT>--enable-clocale=MODEL </TT>
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<DD><P>Select a target-specific underlying locale package. The choices
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are 'gnu' to specify an X/Open (IEEE Std. 1003.1-200x) model based
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on langinfo/iconv (from
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<A HREF="http://sources.redhat.com/glibc/">glibc</A>, the GNU C
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library), or 'generic' to use a generic "C" abstraction
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which consists of "C" locale info. The default is 'generic'.
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</P>
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<DT><TT>--enable-c99 </TT>
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<DD><P>The "long long" type was introduced in C99, along
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with bunches of other functions for wide characters, and math
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classification macros, etc. If enabled, all C99 functions not
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specified by the C++ standard will be put into namespace c99,
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and then all names in the c99 namespace will be injected into
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namespace std, so that C99 functions can be used "as if" they
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were in the C++ standard (as they will eventually be in some
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future revision of the standard, without a doubt.) By default,
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C99 support is on, assuming the configure probes find all the
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necessary functions and bits necessary.
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with bunches of other functions for wide characters, and math
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classification macros, etc. If enabled, all C99 functions not
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specified by the C++ standard will be put into <TT>namespace
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c99</TT>, and then all names in the c99 namespace will be injected
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into namespace std, so that C99 functions can be used "as
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if" they were in the C++ standard (as they will eventually
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be in some future revision of the standard, without a doubt).
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By default, C99 support is on, assuming the configure probes find
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all the necessary functions and bits necessary.
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</P>
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<DT><TT>--enable-long-long </TT>
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<DD><P>The "long long" type was introduced in C99. It is
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provided as a GNU extension to C++98 in g++. This flag builds
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support for "long long" into the library
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(specialized templates and the like for iostreams). This
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option is on by default: if enabled, users will have to either
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use the new-style "C" headers by default (ie cmath
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not math.h) or add appropriate compile-time flags to all
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compile lines to allow "C" visibility of this
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feature (on GNU/Linux, the flag is -D_ISOC99_SOURCE, which is
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added automatically via CPLUSPLUS_CPP_SPEC's addition of
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_GNU_SOURCE).
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support for "long long" into the library (specialized
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templates and the like for iostreams). This option is on by default:
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if enabled, users will have to either use the new-style "C"
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headers by default (i.e., <cmath> not <math.h>)
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or add appropriate compile-time flags to all compile lines to
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allow "C" visibility of this feature (on GNU/Linux,
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the flag is -D_ISOC99_SOURCE, which is added automatically via
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CPLUSPLUS_CPP_SPEC's addition of _GNU_SOURCE).
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</P>
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<DT><TT>--enable-cheaders=OPTION </TT>
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@ -148,14 +147,14 @@ options</A></H1>
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<DT><TT>--enable-version-specific-runtime-libs </TT>
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<DD><P>Specify that run-time libraries should be installed in the
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compiler-specific subdirectory (i.e.,
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<TT>$(libdir)/gcc-lib/$(target_alias)/$(gcc_version)</TT>)
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instead of <TT>$(libdir)</TT>. This option is useful if you
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intend to use several versions of gcc in parallel. In addition,
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libstdc++'s include files will be installed in
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<TT>$(libdir)/gcc-lib/$(target_alias)/$(gcc_version)/include/g++</TT>,
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unless you also specify
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<TT>--with-gxx-include-dir=_dirname_</TT> during configuration.
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compiler-specific subdirectory (i.e.,
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<TT>${libdir}/gcc-lib/${target_alias}/${gcc_version}</TT>)
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instead of <TT>${libdir}</TT>. This option is useful if you
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intend to use several versions of gcc in parallel. In addition,
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libstdc++'s include files will be installed in
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<TT>${libdir}/gcc-lib/${target_alias}/${gcc_version}/include/g++</TT>,
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unless you also specify
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<TT>--with-gxx-include-dir=<EM>dirname</EM></TT> during configuration.
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</P>
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<DT><TT>--with-gxx-include-dir=<include-files dir></TT>
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@ -212,7 +211,7 @@ options</A></H1>
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<HR>
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<P CLASS="fineprint"><EM>
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$Id: configopts.html,v 1.9 2001/04/06 01:47:11 bkoz Exp $
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$Id: configopts.html,v 1.10 2001/04/20 08:59:25 bkoz Exp $
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</EM></P>
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@ -0,0 +1,74 @@
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
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<HTML>
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<HEAD>
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<META NAME="AUTHOR" CONTENT="pme@sources.redhat.com (Phil Edwards)">
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<META NAME="KEYWORDS" CONTENT="libstdc++, libstdc++-v3, GCC, g++">
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<META NAME="DESCRIPTION" CONTENT="Explanatory notes about libstdc++-v3.">
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<META NAME="GENERATOR" CONTENT="vi and eight fingers">
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<TITLE>Explanatory notes about libstdc++-v3 design</TITLE>
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<LINK REL=StyleSheet HREF="lib3styles.css">
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<!-- $Id: configopts.html,v 1.10 2001/04/20 08:59:25 bkoz Exp $ -->
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</HEAD>
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<BODY>
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<H1 CLASS="centered"><A NAME="top">Explanatory notes about libstdc++-v3
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design</A></H1>
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<P>The latest version of this document is always available at
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<A HREF="http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html">
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http://gcc.gnu.org/onlinedocs/libstdc++/explanations.html</A>.
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</P>
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<P>To the <A HREF="http://gcc.gnu.org/libstdc++/">libstdc++-v3 homepage</A>.
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<!-- ####################################################### -->
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<HR>
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<A NAME="cstdio"><H3>"I/O packages", <TT>--enable-cstdio</TT></H3></A>
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<P>In addition to all the nifty things which C++ can do for I/O, its library
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also includes all of the I/O capabilites of C. Making them work together
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can be a challenge, not only
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<A HREF="27_io/howto.html#8">for the programmer</A> but for the
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implementors as well.
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</P>
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<P>There are two ways to do a C++ library: the cool way, and the easy way.
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More specifically, the cool-but-easy-to-get-wrong way, and the
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easy-to-guarantee-correct-behavior way. For 3.0, the easy way is used.
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</P>
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<P>Choosing 'stdio' is the easy way. It builds a C++ library which forwards
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all operations to the C library. Many of the C++ I/O functions are
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specified in the standard 'as if' they called a certain C function; the
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easiest way to get it correct is to actually call that function. The
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disadvantage is that the C++ code will run slower (fortunately, the layer
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is thin).
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</P>
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<P>Choosing 'libio' is the cool way; it allows C++ and C to share some
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buffers. It's disabled because of tricky synchronization issues. Other
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cool ways (various methods of sharing resources between C and C++
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facilities, instead of layering) are possible. This approach can speed
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up I/O significantly.
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</P>
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<P>Other packages are possible. For a new package, a header must be
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written to provide types like streamsize (usually just a typedef), as
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well as some internal types like<TT> __c_file_type </TT> and
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<TT> __c_lock </TT> (for the stdio case, these are FILE (as in
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"FILE*") and a simple POSIX mutex, respectively). An
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interface class called <TT> __basic_file </TT> must also be filled in;
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as an example, for the stdio case, these member functions are all
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inline calles to fread, fwrite, etc.
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</P>
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<P>Return <A HREF="#top">to the top of the page</A> or
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<A HREF="http://gcc.gnu.org/libstdc++/">to the homepage</A>.
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</P>
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<!-- ####################################################### -->
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<HR>
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<P CLASS="fineprint"><EM>
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$Id$
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</EM></P>
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</BODY>
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</HTML>
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Reference in New Issue