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  11     "><link rel="home" href="../index.html" title="The GNU C++ Library"><link rel="up" href="bk01pt02.html" title="Part II.  Standard Contents"><link rel="prev" href="bk01pt02.html" title="Part II.  Standard Contents"><link rel="next" href="dynamic_memory.html" title="Dynamic Memory"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 4.
  12   Support
  13
  14 </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk01pt02.html">Prev</a> </td><th width="60%" align="center">Part II.
  15     Standard Contents
  16   </th><td width="20%" align="right"> <a accesskey="n" href="dynamic_memory.html">Next</a></td></tr></table><hr></div><div class="chapter" title="Chapter 4.  Support"><div class="titlepage"><div><div><h2 class="title"><a name="std.support"></a>Chapter 4.
  17   Support
  18   <a class="indexterm" name="id607999"></a>
  19 </h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><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>
  20     This part deals with the functions called and objects created
  21     automatically during the course of a program's existence.
  22   </p><p>
  23     While we can't reproduce the contents of the Standard here (you
  24     need to get your own copy from your nation's member body; see our
  25     homepage for help), we can mention a couple of changes in what
  26     kind of support a C++ program gets from the Standard Library.
  27   </p><div class="section" title="Types"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="std.support.types"></a>Types</h2></div></div></div><div class="section" title="Fundamental Types"><div class="titlepage"><div><div><h3 class="title"><a name="std.support.types.fundamental"></a>Fundamental Types</h3></div></div></div><p>
  28       C++ has the following builtin types:
  29     </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
  30         char
  31       </p></li><li class="listitem"><p>
  32         signed char
  33       </p></li><li class="listitem"><p>
  34         unsigned char
  35       </p></li><li class="listitem"><p>
  36         signed short
  37       </p></li><li class="listitem"><p>
  38         signed int
  39       </p></li><li class="listitem"><p>
  40         signed long
  41       </p></li><li class="listitem"><p>
  42         unsigned short
  43       </p></li><li class="listitem"><p>
  44         unsigned int
  45       </p></li><li class="listitem"><p>
  46         unsigned long
  47       </p></li><li class="listitem"><p>
  48         bool
  49       </p></li><li class="listitem"><p>
  50         wchar_t
  51       </p></li><li class="listitem"><p>
  52         float
  53       </p></li><li class="listitem"><p>
  54         double
  55       </p></li><li class="listitem"><p>
  56         long double
  57       </p></li></ul></div><p>
  58       These fundamental types are always available, without having to
  59       include a header file. These types are exactly the same in
  60       either C++ or in C.
  61     </p><p>
  62       Specializing parts of the library on these types is prohibited:
  63       instead, use a POD.
  64     </p></div><div class="section" title="Numeric Properties"><div class="titlepage"><div><div><h3 class="title"><a name="std.support.types.numeric_limits"></a>Numeric Properties</h3></div></div></div><p>
  65     The header <code class="filename">limits</code> defines
  66     traits classes to give access to various implementation
  67     defined-aspects of the fundamental types. The traits classes --
  68     fourteen in total -- are all specializations of the template class
  69     <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>
  70     and defined as follows:
  71     </p><pre class="programlisting">
  72    template&lt;typename T&gt;
  73      struct class
  74      {
  75        static const bool is_specialized;
  76        static T max() throw();
  77        static T min() throw();
  78
  79        static const int digits;
  80        static const int digits10;
  81        static const bool is_signed;
  82        static const bool is_integer;
  83        static const bool is_exact;
  84        static const int radix;
  85        static T epsilon() throw();
  86        static T round_error() throw();
  87
  88        static const int min_exponent;
  89        static const int min_exponent10;
  90        static const int max_exponent;
  91        static const int max_exponent10;
  92
  93        static const bool has_infinity;
  94        static const bool has_quiet_NaN;
  95        static const bool has_signaling_NaN;
  96        static const float_denorm_style has_denorm;
  97        static const bool has_denorm_loss;
  98        static T infinity() throw();
  99        static T quiet_NaN() throw();
 100        static T denorm_min() throw();
 101
 102        static const bool is_iec559;
 103        static const bool is_bounded;
 104        static const bool is_modulo;
 105
 106        static const bool traps;
 107        static const bool tinyness_before;
 108        static const float_round_style round_style;
 109      };
 110    </pre></div><div class="section" title="NULL"><div class="titlepage"><div><div><h3 class="title"><a name="std.support.types.null"></a>NULL</h3></div></div></div><p>
 111      The only change that might affect people is the type of
 112      <code class="constant">NULL</code>: while it is required to be a macro,
 113      the definition of that macro is <span class="emphasis"><em>not</em></span> allowed
 114      to be <code class="constant">(void*)0</code>, which is often used in C.
 115     </p><p>
 116      For <span class="command"><strong>g++</strong></span>, <code class="constant">NULL</code> is
 117      <code class="code">#define</code>'d to be
 118      <code class="constant">__null</code>, a magic keyword extension of
 119      <span class="command"><strong>g++</strong></span>.
 120     </p><p>
 121      The biggest problem of #defining <code class="constant">NULL</code> to be
 122      something like <span class="quote">“<span class="quote">0L</span>”</span> is that the compiler will view
 123      that as a long integer before it views it as a pointer, so
 124      overloading won't do what you expect. (This is why
 125      <span class="command"><strong>g++</strong></span> has a magic extension, so that
 126      <code class="constant">NULL</code> is always a pointer.)
 127     </p><p>In his book <a class="link" href="http://www.awprofessional.com/titles/0-201-92488-9/" target="_top"><span class="emphasis"><em>Effective
 128     C++</em></span></a>, Scott Meyers points out that the best way
 129     to solve this problem is to not overload on pointer-vs-integer
 130     types to begin with.  He also offers a way to make your own magic
 131     <code class="constant">NULL</code> that will match pointers before it
 132     matches integers.
 133     </p><p>See
 134       <a class="link" href="http://www.awprofessional.com/titles/0-201-31015-5/" target="_top">the
 135       Effective C++ CD example</a>
 136     </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt02.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="bk01pt02.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.
 137     Standard Contents
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