129 lines
8.3 KiB
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129 lines
8.3 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 4. Support</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="std_contents.html" title="Part II. Standard Contents" /><link rel="prev" href="std_contents.html" title="Part II. Standard Contents" /><link rel="next" href="dynamic_memory.html" title="Dynamic Memory" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 4.
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Support
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</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="std_contents.html">Prev</a> </td><th width="60%" align="center">Part II.
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Standard Contents
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</th><td width="20%" align="right"> <a accesskey="n" href="dynamic_memory.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="std.support"></a>Chapter 4.
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Support
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<a id="id-1.3.4.2.1.1.1" class="indexterm"></a>
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</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="section"><a href="support.html#std.support.types">Types</a></span></dt><dd><dl><dt><span class="section"><a href="support.html#std.support.types.fundamental">Fundamental Types</a></span></dt><dt><span class="section"><a href="support.html#std.support.types.numeric_limits">Numeric Properties</a></span></dt><dt><span class="section"><a href="support.html#std.support.types.null">NULL</a></span></dt></dl></dd><dt><span class="section"><a href="dynamic_memory.html">Dynamic Memory</a></span></dt><dt><span class="section"><a href="termination.html">Termination</a></span></dt><dd><dl><dt><span class="section"><a href="termination.html#support.termination.handlers">Termination Handlers</a></span></dt><dt><span class="section"><a href="termination.html#support.termination.verbose">Verbose Terminate Handler</a></span></dt></dl></dd></dl></div><p>
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This part deals with the functions called and objects created
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automatically during the course of a program's existence.
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</p><p>
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While we can't reproduce the contents of the Standard here (you
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need to get your own copy from your nation's member body; see our
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homepage for help), we can mention a couple of changes in what
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kind of support a C++ program gets from the Standard Library.
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</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.support.types"></a>Types</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="std.support.types.fundamental"></a>Fundamental Types</h3></div></div></div><p>
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C++ has the following builtin types:
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</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
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char
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</p></li><li class="listitem"><p>
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signed char
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</p></li><li class="listitem"><p>
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unsigned char
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</p></li><li class="listitem"><p>
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signed short
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</p></li><li class="listitem"><p>
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signed int
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</p></li><li class="listitem"><p>
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signed long
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</p></li><li class="listitem"><p>
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unsigned short
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</p></li><li class="listitem"><p>
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unsigned int
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</p></li><li class="listitem"><p>
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unsigned long
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</p></li><li class="listitem"><p>
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bool
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</p></li><li class="listitem"><p>
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wchar_t
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</p></li><li class="listitem"><p>
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float
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</p></li><li class="listitem"><p>
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double
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</p></li><li class="listitem"><p>
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long double
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</p></li></ul></div><p>
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These fundamental types are always available, without having to
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include a header file. These types are exactly the same in
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either C++ or in C.
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</p><p>
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Specializing parts of the library on these types is prohibited:
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instead, use a POD.
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</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="std.support.types.numeric_limits"></a>Numeric Properties</h3></div></div></div><p>
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The header <code class="filename">limits</code> defines
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traits classes to give access to various implementation
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defined-aspects of the fundamental types. The traits classes --
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fourteen in total -- are all specializations of the template class
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<code class="classname">numeric_limits</code>, documented <a class="link" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00593.html" target="_top">here</a>
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and defined as follows:
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</p><pre class="programlisting">
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template<typename T>
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struct class
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{
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static const bool is_specialized;
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static T max() throw();
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static T min() throw();
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static const int digits;
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static const int digits10;
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static const bool is_signed;
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static const bool is_integer;
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static const bool is_exact;
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static const int radix;
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static T epsilon() throw();
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static T round_error() throw();
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static const int min_exponent;
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static const int min_exponent10;
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static const int max_exponent;
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static const int max_exponent10;
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static const bool has_infinity;
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static const bool has_quiet_NaN;
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static const bool has_signaling_NaN;
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static const float_denorm_style has_denorm;
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static const bool has_denorm_loss;
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static T infinity() throw();
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static T quiet_NaN() throw();
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static T denorm_min() throw();
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static const bool is_iec559;
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static const bool is_bounded;
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static const bool is_modulo;
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static const bool traps;
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static const bool tinyness_before;
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static const float_round_style round_style;
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};
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</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="std.support.types.null"></a>NULL</h3></div></div></div><p>
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The only change that might affect people is the type of
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<code class="constant">NULL</code>: while it is required to be a macro,
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the definition of that macro is <span class="emphasis"><em>not</em></span> allowed
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to be <code class="constant">(void*)0</code>, which is often used in C.
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</p><p>
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For <span class="command"><strong>g++</strong></span>, <code class="constant">NULL</code> is
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<code class="code">#define</code>'d to be
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<code class="constant">__null</code>, a magic keyword extension of
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<span class="command"><strong>g++</strong></span>.
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</p><p>
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The biggest problem of #defining <code class="constant">NULL</code> to be
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something like <span class="quote">“<span class="quote">0L</span>”</span> is that the compiler will view
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that as a long integer before it views it as a pointer, so
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overloading won't do what you expect. (This is why
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<span class="command"><strong>g++</strong></span> has a magic extension, so that
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<code class="constant">NULL</code> is always a pointer.)
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</p><p>In his book <a class="link" href="http://www.aristeia.com/books.html" target="_top"><span class="emphasis"><em>Effective
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C++</em></span></a>, Scott Meyers points out that the best way
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to solve this problem is to not overload on pointer-vs-integer
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types to begin with. He also offers a way to make your own magic
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<code class="constant">NULL</code> that will match pointers before it
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matches integers.
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</p><p>See the
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<a class="link" href="http://www.aristeia.com/books.html" target="_top"><span class="emphasis"><em>Effective
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C++ CD</em></span></a> example.
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</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="std_contents.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="std_contents.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="dynamic_memory.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part II.
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Standard Contents
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</td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Dynamic Memory</td></tr></table></div></body></html> |