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   3 <html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 4.  Support</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    "/><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      runtime&#10;    , &#10;      library&#10;    "/><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><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 4.
   4   Support
   5
   6 </th></tr><tr><td align="left"><a accesskey="p" href="bk01pt02.html">Prev</a> </td><th width="60%" align="center">Part II.
   7     Standard Contents
   8   </th><td 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 id="std.support"/>Chapter 4.
   9   Support
  10   <a id="id442234" class="indexterm"/>
  11 </h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></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>
  12     This part deals with the functions called and objects created
  13     automatically during the course of a program's existence.
  14   </p><p>
  15     While we can't reproduce the contents of the Standard here (you
  16     need to get your own copy from your nation's member body; see our
  17     homepage for help), we can mention a couple of changes in what
  18     kind of support a C++ program gets from the Standard Library.
  19   </p><div class="section" title="Types"><div class="titlepage"><div><div><h2 class="title"><a id="std.support.types"/>Types</h2></div></div></div><div class="section" title="Fundamental Types"><div class="titlepage"><div><div><h3 class="title"><a id="std.support.types.fundamental"/>Fundamental Types</h3></div></div></div><p>
  20       C++ has the following builtin types:
  21     </p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
  22         char
  23       </p></li><li class="listitem"><p>
  24         signed char
  25       </p></li><li class="listitem"><p>
  26         unsigned char
  27       </p></li><li class="listitem"><p>
  28         signed short
  29       </p></li><li class="listitem"><p>
  30         signed int
  31       </p></li><li class="listitem"><p>
  32         signed long
  33       </p></li><li class="listitem"><p>
  34         unsigned short
  35       </p></li><li class="listitem"><p>
  36         unsigned int
  37       </p></li><li class="listitem"><p>
  38         unsigned long
  39       </p></li><li class="listitem"><p>
  40         bool
  41       </p></li><li class="listitem"><p>
  42         wchar_t
  43       </p></li><li class="listitem"><p>
  44         float
  45       </p></li><li class="listitem"><p>
  46         double
  47       </p></li><li class="listitem"><p>
  48         long double
  49       </p></li></ul></div><p>
  50       These fundamental types are always available, without having to
  51       include a header file. These types are exactly the same in
  52       either C++ or in C.
  53     </p><p>
  54       Specializing parts of the library on these types is prohibited:
  55       instead, use a POD.
  56     </p></div><div class="section" title="Numeric Properties"><div class="titlepage"><div><div><h3 class="title"><a id="std.support.types.numeric_limits"/>Numeric Properties</h3></div></div></div><p>
  57     The header <code class="filename">limits</code> defines
  58     traits classes to give access to various implementation
  59     defined-aspects of the fundamental types. The traits classes --
  60     fourteen in total -- are all specializations of the template class
  61     <code class="classname">numeric_limits</code>, documented <a class="link" href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00593.html">here</a>
  62     and defined as follows:
  63     </p><pre class="programlisting">
  64    template&lt;typename T&gt;
  65      struct class
  66      {
  67        static const bool is_specialized;
  68        static T max() throw();
  69        static T min() throw();
  70
  71        static const int digits;
  72        static const int digits10;
  73        static const bool is_signed;
  74        static const bool is_integer;
  75        static const bool is_exact;
  76        static const int radix;
  77        static T epsilon() throw();
  78        static T round_error() throw();
  79
  80        static const int min_exponent;
  81        static const int min_exponent10;
  82        static const int max_exponent;
  83        static const int max_exponent10;
  84
  85        static const bool has_infinity;
  86        static const bool has_quiet_NaN;
  87        static const bool has_signaling_NaN;
  88        static const float_denorm_style has_denorm;
  89        static const bool has_denorm_loss;
  90        static T infinity() throw();
  91        static T quiet_NaN() throw();
  92        static T denorm_min() throw();
  93
  94        static const bool is_iec559;
  95        static const bool is_bounded;
  96        static const bool is_modulo;
  97
  98        static const bool traps;
  99        static const bool tinyness_before;
 100        static const float_round_style round_style;
 101      };
 102    </pre></div><div class="section" title="NULL"><div class="titlepage"><div><div><h3 class="title"><a id="std.support.types.null"/>NULL</h3></div></div></div><p>
 103      The only change that might affect people is the type of
 104      <code class="constant">NULL</code>: while it is required to be a macro,
 105      the definition of that macro is <span class="emphasis"><em>not</em></span> allowed
 106      to be <code class="constant">(void*)0</code>, which is often used in C.
 107     </p><p>
 108      For <span class="command"><strong>g++</strong></span>, <code class="constant">NULL</code> is
 109      <code class="code">#define</code>'d to be
 110      <code class="constant">__null</code>, a magic keyword extension of
 111      <span class="command"><strong>g++</strong></span>.
 112     </p><p>
 113      The biggest problem of #defining <code class="constant">NULL</code> to be
 114      something like <span class="quote">“<span class="quote">0L</span>”</span> is that the compiler will view
 115      that as a long integer before it views it as a pointer, so
 116      overloading won't do what you expect. (This is why
 117      <span class="command"><strong>g++</strong></span> has a magic extension, so that
 118      <code class="constant">NULL</code> is always a pointer.)
 119     </p><p>In his book <a class="link" href="http://www.awprofessional.com/titles/0-201-92488-9/"><span class="emphasis"><em>Effective
 120     C++</em></span></a>, Scott Meyers points out that the best way
 121     to solve this problem is to not overload on pointer-vs-integer
 122     types to begin with.  He also offers a way to make your own magic
 123     <code class="constant">NULL</code> that will match pointers before it
 124     matches integers.
 125     </p><p>See
 126       <a class="link" href="http://www.awprofessional.com/titles/0-201-31015-5/">the
 127       Effective C++ CD example</a>
 128     </p></div></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="bk01pt02.html">Prev</a> </td><td align="center"><a accesskey="u" href="bk01pt02.html">Up</a></td><td align="right"> <a accesskey="n" href="dynamic_memory.html">Next</a></td></tr><tr><td align="left" valign="top">Part II.
 129     Standard Contents
 130    </td><td align="center"><a accesskey="h" href="../index.html">Home</a></td><td align="right" valign="top"> Dynamic Memory</td></tr></table></div></body></html>