1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> 5<title>Using the predefs</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../predef.html" title="Chapter 29. Boost.Predef 1.10"> 10<link rel="prev" href="../predef.html" title="Chapter 29. Boost.Predef 1.10"> 11<link rel="next" href="adding_new_predefs.html" title="Adding new predefs"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="../predef.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../predef.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="adding_new_predefs.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="predef.using_the_predefs"></a><a class="link" href="using_the_predefs.html" title="Using the predefs">Using the predefs</a> 29</h2></div></div></div> 30<p> 31 To use the automatically defined predefs one needs to only include the single 32 top-level header: 33 </p> 34<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">predef</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span> 35</pre> 36<p> 37 This defines <span class="bold"><strong>all</strong></span> the version macros known 38 to the library. For each macro it will be defined to either a <span class="emphasis"><em>zero</em></span> 39 valued expression for when the particular item is not detected, and to a <span class="emphasis"><em>positive</em></span> 40 value if it is detected. The predef macros fall onto five categories each with 41 macros of a particular prefix: 42 </p> 43<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 44<li class="listitem"> 45 <code class="computeroutput"><span class="identifier">BOOST_ARCH_</span></code>for system/CPU 46 architecture one is compiling for. 47 </li> 48<li class="listitem"> 49 <code class="computeroutput"><span class="identifier">BOOST_COMP_</span></code> for the compiler 50 one is using. 51 </li> 52<li class="listitem"> 53 <code class="computeroutput"><span class="identifier">BOOST_LANG_</span></code> for language 54 standards one is compiling against. 55 </li> 56<li class="listitem"> 57 <code class="computeroutput"><span class="identifier">BOOST_LIB_C_</span></code> and <code class="computeroutput"><span class="identifier">BOOST_LIB_STD_</span></code> for the C and C++ standard 58 library in use. 59 </li> 60<li class="listitem"> 61 <code class="computeroutput"><span class="identifier">BOOST_OS_</span></code> for the operating 62 system we are compiling to. 63 </li> 64<li class="listitem"> 65 <code class="computeroutput"><span class="identifier">BOOST_PLAT_</span></code> for platforms 66 on top of operating system or compilers. 67 </li> 68<li class="listitem"> 69 <code class="computeroutput"><span class="identifier">BOOST_ENDIAN_</span></code> for endianness 70 of the os and architecture combination. 71 </li> 72<li class="listitem"> 73 <code class="computeroutput"><span class="identifier">BOOST_HW_</span></code> for hardware 74 specific features. 75 </li> 76<li class="listitem"> 77 <code class="computeroutput"><span class="identifier">BOOST_HW_SIMD</span></code> for SIMD 78 (Single Instruction Multiple Data) detection. 79 </li> 80</ul></div> 81<div class="note"><table border="0" summary="Note"> 82<tr> 83<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td> 84<th align="left">Note</th> 85</tr> 86<tr><td align="left" valign="top"><p> 87 The detected definitions are for the configuration one is targeting during 88 the compile. In particular in a cross-compile this means the target system, 89 and not the host system. 90 </p></td></tr> 91</table></div> 92<p> 93 One uses the individual definitions to compare against specific versions by 94 comparing against the <code class="computeroutput"><span class="identifier">BOOST_VERSION_NUMBER</span></code> 95 macro. For example, to make a choice based on the version of the GCC C++ compiler 96 one would: 97 </p> 98<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">predef</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span> 99<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 100 101<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 102<span class="special">{</span> 103 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">BOOST_COMP_GNUC</span> <span class="special">>=</span> <span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="number">4</span><span class="special">,</span><span class="number">0</span><span class="special">,</span><span class="number">0</span><span class="special">))</span> 104 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"GCC compiler is at least version 4.0.0"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 105 <span class="keyword">else</span> 106 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"GCC compiler is at older than version 4.0.0, or not a GCC compiler"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 107 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 108<span class="special">}</span> 109</pre> 110<p> 111 As you might notice above the <code class="computeroutput"><span class="keyword">else</span></code> 112 clause also covers the case where the particular compiler is not detected. 113 But one can make the test also test for the detection. All predef definitions 114 are defined as a zero (0) expression when not detected. Hence one could use 115 the detection with a natural single condition. For example: 116 </p> 117<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">predef</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span> 118<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 119 120<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 121<span class="special">{</span> 122 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">BOOST_COMP_GNUC</span><span class="special">)</span> 123 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"This is GNU GCC!"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 124 <span class="keyword">else</span> 125 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Not GNU GCC."</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 126 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 127<span class="special">}</span> 128</pre> 129<p> 130 And since the predef's are preprocessor definitions the same is possible from 131 the preprocessor: 132 </p> 133<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">predef</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span> 134<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 135 136<span class="preprocessor">#if</span> <span class="identifier">BOOST_COMP_GNUC</span> 137 <span class="preprocessor">#if</span> <span class="identifier">BOOST_COMP_GNUC</span> <span class="special">>=</span> <span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="number">4</span><span class="special">,</span><span class="number">0</span><span class="special">,</span><span class="number">0</span><span class="special">)</span> 138 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span> <span class="identifier">the_compiler</span> <span class="special">=</span> <span class="string">"GNU GCC, of at least version 4."</span> 139 <span class="preprocessor">#else</span> 140 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span> <span class="identifier">the_compiler</span> <span class="special">=</span> <span class="string">"GNU GCC, less than version 4."</span> 141 <span class="preprocessor">#endif</span> 142<span class="preprocessor">#else</span> 143 <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span> <span class="identifier">the_compiler</span> <span class="special">=</span> <span class="string">"Not GNU GCC."</span> 144<span class="preprocessor">#endif</span> 145 146<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 147<span class="special">{</span> 148 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">the_compiler</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 149 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 150<span class="special">}</span> 151</pre> 152<p> 153 In addition, for each version macro defined there is an <code class="computeroutput"><span class="special">*</span><span class="identifier">_AVAILABLE</span></code> macro defined only when the particular 154 aspect is detected. I.e. a definition equivalent to: 155 </p> 156<pre class="programlisting"><span class="preprocessor">#if</span> <span class="identifier">BOOST_PREDEF_ABC</span> 157 <span class="preprocessor">#define</span> <span class="identifier">BOOST_PREDEF_ABC_AVAILABLE</span> 158<span class="preprocessor">#endif</span> 159</pre> 160<p> 161 Also for each aspect there is a macro defined with a descriptive name of what 162 the detection is. 163 </p> 164<h4> 165<a name="predef.using_the_predefs.h0"></a> 166 <span class="phrase"><a name="predef.using_the_predefs.the_emulated_macros"></a></span><a class="link" href="using_the_predefs.html#predef.using_the_predefs.the_emulated_macros">The 167 <code class="computeroutput"><span class="special">*</span><span class="identifier">_EMULATED</span></code> 168 macros</a> 169 </h4> 170<p> 171 Predef definitions are guaranteed to be uniquely detected within one category. 172 But there are contexts under which multiple underlying detections are possible. 173 The well known example of this is detection of GCC and MSVC compilers which 174 are commonly emulated by other compilers by defining the same base macros. 175 To account for this detection headers are allowed to define <code class="computeroutput"><span class="special">*</span><span class="identifier">_EMULATED</span></code> predefs when this situation is 176 detected. The emulated predefs will be set to the version number of the detection 177 instead of the regular predef macro for that detection. For example MSVC will 178 set <code class="computeroutput"><span class="identifier">BOOST_COMP_MSVC_EMULATED</span></code> 179 but not set <code class="computeroutput"><span class="identifier">BOOST_COMP_MSVC</span></code>, 180 and it will also set <code class="computeroutput"><span class="identifier">BOOST_COMP_MSVC_AVAILABLE</span></code>. 181 </p> 182<h4> 183<a name="predef.using_the_predefs.h1"></a> 184 <span class="phrase"><a name="predef.using_the_predefs.using_the_boost_version_number_m"></a></span><a class="link" href="using_the_predefs.html#predef.using_the_predefs.using_the_boost_version_number_m">Using the 185 <code class="computeroutput"><span class="identifier">BOOST_VERSION_NUMBER</span></code> macro</a> 186 </h4> 187<p> 188 All the predefs are defined to be a use of the <code class="computeroutput"><span class="identifier">BOOST_VERSION_NUMBER</span></code> 189 macro. The macro takes individual major, minor, and patch value expressions: 190 </p> 191<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span> <span class="identifier">major</span><span class="special">,</span> <span class="identifier">minor</span><span class="special">,</span> <span class="identifier">patch</span> <span class="special">)</span> <span class="special">...</span> 192</pre> 193<p> 194 The arguments are: 195 </p> 196<div class="orderedlist"><ol class="orderedlist" type="1"> 197<li class="listitem"> 198 Major version number, as a constant value expression in the range [0,99]. 199 </li> 200<li class="listitem"> 201 Minor version number, as a constant value expression in the range [0,99]. 202 </li> 203<li class="listitem"> 204 Patch-level version number, as a constant value expression in the range 205 [0,99999]. 206 </li> 207</ol></div> 208<p> 209 The ranges for each are "enforced" by the use of a modulo ("%"), 210 i.e. truncation, as opposed to a clamp. And hence this means that the limits 211 are enforced only enough to keep from having out-of-range problems. But not 212 enough to prevent other kinds of problems. Like exceeding the range and getting 213 false detections, or non-detections. It is up to the individual predefs to 214 ensure correct usage beyond the range guarantee. 215 </p> 216<p> 217 The values for the arguments can be any preprocessor valid constant value expression. 218 Only constant value arithmetic is used in the definition of the <code class="computeroutput"><span class="identifier">BOOST_VERSION_NUMBER</span></code> macro and in any of 219 the other predef macros. This means that any allowed base is possible, i.e. 220 binary, octal, decimal, and hexadecimal. For example: 221 </p> 222<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">MY_APPLICATION_VERSION_NUMBER</span> <span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="number">2</span><span class="special">,</span><span class="number">0xA</span><span class="special">,</span><span class="number">015</span><span class="special">)</span> 223</pre> 224<p> 225 Is equivalent to: 226 </p> 227<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">MY_APPLICATION_VERSION_NUMBER</span> <span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="number">2</span><span class="special">,</span><span class="number">10</span><span class="special">,</span><span class="number">13</span><span class="special">)</span> 228</pre> 229</div> 230<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 231<td align="left"></td> 232<td align="right"><div class="copyright-footer">Copyright © 2005-2019 Rene Rivera<br>Copyright © 2015 Charly Chevalier<br>Copyright © 2015 Joel Falcou<p> 233 Distributed under the Boost Software License, Version 1.0. (See accompanying 234 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 235 </p> 236</div></td> 237</tr></table> 238<hr> 239<div class="spirit-nav"> 240<a accesskey="p" href="../predef.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../predef.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="adding_new_predefs.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 241</div> 242</body> 243</html> 244
