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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="predef.check_utilities"></a><a class="link" href="check_utilities.html" title="Check Utilities">Check Utilities</a>
</h2></div></div></div>
<p>
The <code class="computeroutput"><span class="identifier">predef_check</span></code> utility provides
a facility for building a program that will check a given set of expressions
against the definitions it detected when it was built.
</p>
<h4>
<a name="predef.check_utilities.h0"></a>
<span class="phrase"><a name="predef.check_utilities.predef_check_programs"></a></span><a class="link" href="check_utilities.html#predef.check_utilities.predef_check_programs"><code class="literal">predef_check</code>
programs</a>
</h4>
<p>
Even though there is only one <code class="computeroutput"><span class="identifier">predef_check</span></code>
program, there are variations for each of the languages that are detected by
Predef to match the convention for sources files. For all of them one invokes
with a list of expression arguments. The expressions are evaluated within the
context of the particular <code class="literal">predef_check</code> program and if they
all are true zero (0) is returned. Otherwise the index of the first false expression
is returned.
</p>
<p>
The expression syntax is simple:
</p>
<pre class="programlisting">predef-definition [ relational-operator version-value ]
</pre>
<p>
<em class="replaceable"><code>predef-definition</code></em> can be any of the Predef definitions.
For example <code class="computeroutput"><span class="identifier">BOOST_COMP_GCC</span></code>.
</p>
<p>
<em class="replaceable"><code>relational-operator</code></em> can be any of: <code class="literal">></code>,
<code class="literal"><</code>, <code class="literal">>=</code>, <code class="literal"><=</code>,
<code class="literal">==</code> and <code class="literal">!=</code>.
</p>
<p>
<em class="replaceable"><code>version-number</code></em> can be a full or partial version
triplet value. If it's a partial version triple it is completed with zeros.
That is <code class="literal">x.y</code> is equivalent to <code class="literal">x.y.0</code> and
<code class="literal">x</code> is equivalent to <code class="literal">x.0.0</code>.
</p>
<p>
The <em class="replaceable"><code>relations-operator</code></em> and <em class="replaceable"><code>version-number</code></em>
can be ommited. In which case it is equivalent to:
</p>
<pre class="programlisting">predef-definition > 0.0.0
</pre>
<h4>
<a name="predef.check_utilities.h1"></a>
<span class="phrase"><a name="predef.check_utilities.using_with_boost_build"></a></span><a class="link" href="check_utilities.html#predef.check_utilities.using_with_boost_build">Using
with Boost.Build</a>
</h4>
<p>
You can use the <code class="literal">predef_check</code> programs directly from Boost
Build to configure target requirements. This is useful for controlling what
gets built as part of your project based on the detailed version information
available in Predef. The basic use is simple:
</p>
<pre class="programlisting">import path-to-predef-src/tools/check/predef
: check require
: predef-check predef-require ;
exe my_windows_program : windows_source.cpp
: [ predef-require "BOOST_OS_WINDOWS" ] ;
</pre>
<p>
That simple use case will skip building the <code class="literal">my_windows_program</code>
unless one is building for Windows. Like the direct <code class="literal">predef_check</code>
you can pass mutiple expressions using relational comparisons. For example:
</p>
<pre class="programlisting">import path-to-predef-src/tools/check/predef
: check require
: predef-check predef-require ;
lib my_special_lib : source.cpp
: [ predef-require "BOOST_OS_WINDOWS != 0" "BOOST_OS_VMS != 0"] ;
</pre>
<p>
And in that case the <code class="literal">my_special_lib</code> is built only when the
OS is not Windows or VMS. The <code class="literal">requires</code> rule is a special
case of the <code class="literal">check</code> rule. And is defined in terms of it:
</p>
<pre class="programlisting">rule require ( expressions + : language ? )
{
return [ check $(expressions) : $(language) : : <build>no ] ;
}
</pre>
<p>
The expression can also use explicit "and", "or" logical
operators to for more complex checks:
</p>
<pre class="programlisting">import path-to-predef-src/tools/check/predef
: check require
: predef-check predef-require ;
lib my_special_lib : source.cpp
: [ predef-require "BOOST_OS_WINDOWS" or "BOOST_OS_VMS"] ;
</pre>
<p>
You can use the <code class="literal">check</code> rule for more control and to implement
something other than control of what gets built. The definition for the <code class="literal">check</code>
rule is:
</p>
<pre class="programlisting">rule check ( expressions + : language ? : true-properties * : false-properties * )
</pre>
<p>
When invoked as a reuirement of a Boost Build target this rule will add the
<code class="literal">true-properties</code> to the target if all the <code class="literal">expressions</code>
evaluate to true. Otherwise the <code class="literal">false-properties</code> get added
as requirements. For example you could use it to enable or disable features
in your programs:
</p>
<pre class="programlisting">import path-to-predef-src/tools/check/predef
: check require
: predef-check predef-require ;
exe my_special_exe : source.cpp
: [ predef-check "BOOST_OS_WINDOWS == 0"
: : <define>ENABLE_WMF=0
: <define>ENABLE_WMF=1 ] ;
</pre>
<p>
For both <code class="literal">check</code> and <code class="literal">require</code> the <code class="literal">language</code>
argument controls which variant of the <code class="literal">predef_check</code> program
is used to check the expressions. It defaults to "c++", but can be
any of: "c", "cpp", "objc", and "objcpp".
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2005-2016 Rene Rivera<br>Copyright © 2015 Charly Chevalier<br>Copyright © 2015 Joel Falcou<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
</p>
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