14fee23f9Smrg<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2d79abf08Smrg<!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. 34fee23f9Smrg Support 44fee23f9Smrg 548fb7bfaSmrg</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. 648fb7bfaSmrg Standard Contents 748fb7bfaSmrg </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. 84fee23f9Smrg Support 94d5abbe8Smrg <a id="id-1.3.4.2.1.1.1" class="indexterm"></a> 10*fb8a8121Smrg</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><dd><dl><dt><span class="section"><a href="dynamic_memory.html#std.support.memory.notes">Additional Notes</a></span></dt></dl></dd><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> 1148fb7bfaSmrg This part deals with the functions called and objects created 1248fb7bfaSmrg automatically during the course of a program's existence. 1348fb7bfaSmrg </p><p> 1448fb7bfaSmrg While we can't reproduce the contents of the Standard here (you 1548fb7bfaSmrg need to get your own copy from your nation's member body; see our 1648fb7bfaSmrg homepage for help), we can mention a couple of changes in what 1748fb7bfaSmrg kind of support a C++ program gets from the Standard Library. 1848fb7bfaSmrg </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> 1948fb7bfaSmrg C++ has the following builtin types: 2048fb7bfaSmrg </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> 2148fb7bfaSmrg char 2248fb7bfaSmrg </p></li><li class="listitem"><p> 2348fb7bfaSmrg signed char 2448fb7bfaSmrg </p></li><li class="listitem"><p> 2548fb7bfaSmrg unsigned char 2648fb7bfaSmrg </p></li><li class="listitem"><p> 2748fb7bfaSmrg signed short 2848fb7bfaSmrg </p></li><li class="listitem"><p> 2948fb7bfaSmrg signed int 3048fb7bfaSmrg </p></li><li class="listitem"><p> 3148fb7bfaSmrg signed long 3248fb7bfaSmrg </p></li><li class="listitem"><p> 3348fb7bfaSmrg unsigned short 3448fb7bfaSmrg </p></li><li class="listitem"><p> 3548fb7bfaSmrg unsigned int 3648fb7bfaSmrg </p></li><li class="listitem"><p> 3748fb7bfaSmrg unsigned long 3848fb7bfaSmrg </p></li><li class="listitem"><p> 3948fb7bfaSmrg bool 4048fb7bfaSmrg </p></li><li class="listitem"><p> 4148fb7bfaSmrg wchar_t 4248fb7bfaSmrg </p></li><li class="listitem"><p> 4348fb7bfaSmrg float 4448fb7bfaSmrg </p></li><li class="listitem"><p> 4548fb7bfaSmrg double 4648fb7bfaSmrg </p></li><li class="listitem"><p> 4748fb7bfaSmrg long double 4848fb7bfaSmrg </p></li></ul></div><p> 4948fb7bfaSmrg These fundamental types are always available, without having to 5048fb7bfaSmrg include a header file. These types are exactly the same in 5148fb7bfaSmrg either C++ or in C. 5248fb7bfaSmrg </p><p> 5348fb7bfaSmrg Specializing parts of the library on these types is prohibited: 5448fb7bfaSmrg instead, use a POD. 5548fb7bfaSmrg </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> 56*fb8a8121Smrg The header <code class="filename"><limits></code> defines 5748fb7bfaSmrg traits classes to give access to various implementation 5848fb7bfaSmrg defined-aspects of the fundamental types. The traits classes -- 59181254a7Smrg fourteen in total -- are all specializations of the class template 60181254a7Smrg <code class="classname">numeric_limits</code> 6148fb7bfaSmrg and defined as follows: 6248fb7bfaSmrg </p><pre class="programlisting"> 6348fb7bfaSmrg template<typename T> 6448fb7bfaSmrg struct class 6548fb7bfaSmrg { 6648fb7bfaSmrg static const bool is_specialized; 6748fb7bfaSmrg static T max() throw(); 6848fb7bfaSmrg static T min() throw(); 6948fb7bfaSmrg 7048fb7bfaSmrg static const int digits; 7148fb7bfaSmrg static const int digits10; 7248fb7bfaSmrg static const bool is_signed; 7348fb7bfaSmrg static const bool is_integer; 7448fb7bfaSmrg static const bool is_exact; 7548fb7bfaSmrg static const int radix; 7648fb7bfaSmrg static T epsilon() throw(); 7748fb7bfaSmrg static T round_error() throw(); 7848fb7bfaSmrg 7948fb7bfaSmrg static const int min_exponent; 8048fb7bfaSmrg static const int min_exponent10; 8148fb7bfaSmrg static const int max_exponent; 8248fb7bfaSmrg static const int max_exponent10; 8348fb7bfaSmrg 8448fb7bfaSmrg static const bool has_infinity; 8548fb7bfaSmrg static const bool has_quiet_NaN; 8648fb7bfaSmrg static const bool has_signaling_NaN; 8748fb7bfaSmrg static const float_denorm_style has_denorm; 8848fb7bfaSmrg static const bool has_denorm_loss; 8948fb7bfaSmrg static T infinity() throw(); 9048fb7bfaSmrg static T quiet_NaN() throw(); 9148fb7bfaSmrg static T denorm_min() throw(); 9248fb7bfaSmrg 9348fb7bfaSmrg static const bool is_iec559; 9448fb7bfaSmrg static const bool is_bounded; 9548fb7bfaSmrg static const bool is_modulo; 9648fb7bfaSmrg 9748fb7bfaSmrg static const bool traps; 9848fb7bfaSmrg static const bool tinyness_before; 9948fb7bfaSmrg static const float_round_style round_style; 10048fb7bfaSmrg }; 10148fb7bfaSmrg </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> 10248fb7bfaSmrg The only change that might affect people is the type of 10348fb7bfaSmrg <code class="constant">NULL</code>: while it is required to be a macro, 10448fb7bfaSmrg the definition of that macro is <span class="emphasis"><em>not</em></span> allowed 105*fb8a8121Smrg to be an expression with pointer type such as 106*fb8a8121Smrg <code class="constant">(void*)0</code>, which is often used in C. 10748fb7bfaSmrg </p><p> 10848fb7bfaSmrg For <span class="command"><strong>g++</strong></span>, <code class="constant">NULL</code> is 10948fb7bfaSmrg <code class="code">#define</code>'d to be 11048fb7bfaSmrg <code class="constant">__null</code>, a magic keyword extension of 111*fb8a8121Smrg <span class="command"><strong>g++</strong></span> that is slightly safer than a plain integer. 11248fb7bfaSmrg </p><p> 11348fb7bfaSmrg The biggest problem of #defining <code class="constant">NULL</code> to be 11448fb7bfaSmrg something like <span class="quote">“<span class="quote">0L</span>”</span> is that the compiler will view 11548fb7bfaSmrg that as a long integer before it views it as a pointer, so 116*fb8a8121Smrg overloading won't do what you expect. It might not even have the 117*fb8a8121Smrg same size as a pointer, so passing <code class="constant">NULL</code> to a 118*fb8a8121Smrg varargs function where a pointer is expected might not even work 119*fb8a8121Smrg correctly if <code class="code">sizeof(NULL) < sizeof(void*)</code>. 120*fb8a8121Smrg The G++ <code class="constant">__null</code> extension is defined so that 121*fb8a8121Smrg <code class="code">sizeof(__null) == sizeof(void*)</code> to avoid this problem. 122*fb8a8121Smrg </p><p> 123*fb8a8121Smrg Scott Meyers explains this in more detail in his book 124*fb8a8121Smrg <a class="link" href="https://www.aristeia.com/books.html" target="_top"><span class="emphasis"><em>Effective 125*fb8a8121Smrg Modern C++</em></span></a> and as a guideline to solve this problem 126*fb8a8121Smrg recommends to not overload on pointer-vs-integer types to begin with. 127*fb8a8121Smrg </p><p> 128*fb8a8121Smrg The C++ 2011 standard added the <code class="constant">nullptr</code> keyword, 129*fb8a8121Smrg which is a null pointer constant of a special type, 130*fb8a8121Smrg <code class="classname">std::nullptr_t</code>. Values of this type can be 131*fb8a8121Smrg implicitly converted to <span class="emphasis"><em>any</em></span> pointer type, 132*fb8a8121Smrg and cannot convert to integer types or be deduced as an integer type. 133*fb8a8121Smrg Unless you need to be compatible with C++98/C++03 or C you should prefer 134*fb8a8121Smrg to use <code class="constant">nullptr</code> instead of <code class="constant">NULL</code>. 13548fb7bfaSmrg </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. 13648fb7bfaSmrg Standard Contents 13748fb7bfaSmrg </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>