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15<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./macros.html" class="navigation-link">Macros</a> / <a href="./asserts.html" class="navigation-link">Asserts</a> / <a href="./assert-relation.html" class="navigation-link">BOOST_MPL_ASSERT_RELATION</a></td>
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17<div class="section" id="assert-relation">
18<h1><a class="toc-backref" href="./asserts.html#id514" name="assert-relation">BOOST_MPL_ASSERT_RELATION</a></h1>
19<div class="section" id="the-macros-asserts-assert-synopsis">
20<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
21<pre class="literal-block">
22#define <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( x, relation, y ) \
23    <em>unspecified token sequence</em> \
24/**/
25</pre>
26</div>
27<div class="section" id="the-macros-asserts-assert-description">
28<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
29<p>A specialized assertion macro for checking numerical conditions. Generates
30a compilation error when the condition <tt class="literal"><span class="pre">(</span> <span class="pre">x</span> <span class="pre">relation</span> <span class="pre">y</span> <span class="pre">)</span></tt> 
31doesn't hold.</p>
32</div>
33<div class="section" id="the-macros-asserts-assert-header">
34<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
35<pre class="literal-block">
36#include &lt;<a href="../../../../boost/mpl/assert.hpp" class="header">boost/mpl/assert.hpp</a>&gt;
37</pre>
38</div>
39<div class="section" id="the-macros-asserts-assert-parameters">
40<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
41<table border="1" class="table">
42<colgroup>
43<col width="15%" />
44<col width="36%" />
45<col width="48%" />
46</colgroup>
47<thead valign="bottom">
48<tr><th>Parameter</th>
49<th>Requirement</th>
50<th>Description</th>
51</tr>
52</thead>
53<tbody valign="top">
54<tr><td><tt class="literal"><span class="pre">x</span></tt></td>
55<td>An integral constant</td>
56<td>Left operand of the checked relation.</td>
57</tr>
58<tr><td><tt class="literal"><span class="pre">y</span></tt></td>
59<td>An integral constant</td>
60<td>Right operand of the checked relation.</td>
61</tr>
62<tr><td><tt class="literal"><span class="pre">relation</span></tt></td>
63<td>A C++ operator token</td>
64<td>An operator token for the relation being
65checked.</td>
66</tr>
67</tbody>
68</table>
69</div>
70<div class="section" id="the-macros-asserts-assert-expression-semantics">
71<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
72<p>For any integral constants <tt class="literal"><span class="pre">x</span></tt>, <tt class="literal"><span class="pre">y</span></tt> and a legal C++ operator token <tt class="literal"><span class="pre">op</span></tt>:</p>
73<pre class="literal-block">
74<a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( x, op, y );
75</pre>
76<table class="field-list" frame="void" rules="none">
77<col class="field-name" />
78<col class="field-body" />
79<tbody valign="top">
80<tr class="field"><th class="field-name">Return type:</th><td class="field-body">None.</td>
81</tr>
82<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Generates a compilation error if <tt class="literal"><span class="pre">(</span> <span class="pre">x</span> <span class="pre">op</span> <span class="pre">y</span> <span class="pre">)</span> <span class="pre">!=</span> <span class="pre">true</span></tt>, otherwise
83has no effect.</p>
84<p>When possible within the compiler's diagnostic capabilities,
85the error message will include a name of the relation being checked,
86the actual values of both operands, and have a general form of:</p>
87<pre class="last literal-block">
88<em>...</em> ************<em>...</em>assert_relation&lt;op, x, y&gt;::************) <em>...</em>
89</pre>
90</td>
91</tr>
92</tbody>
93</table>
94</div>
95<div class="section" id="the-macros-asserts-assert-example">
96<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
97<pre class="literal-block">
98template&lt; typename T, typename U &gt; struct my
99{
100    // ...
101    <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( sizeof(T), &lt;, sizeof(U) );
102};
103
104my&lt;char[50],char[10]&gt; test;
105
106// In instantiation of `my&lt;char[50], char[10]&gt;':
107//   instantiated from here
108// conversion from `
109//   mpl_::failed************mpl_::assert_relation&lt;<a href="./less.html" class="identifier">less</a>, 50, 10&gt;::************'
110//   to non-scalar type `mpl_::assert&lt;false&gt;' requested
111</pre>
112</div>
113<div class="section" id="the-macros-asserts-assert-see-also">
114<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
115<p><a class="reference" href="./asserts.html">Asserts</a>, <a class="refentry reference" href="./assert.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_ASSERT</span></tt></a>, <a class="refentry reference" href="./assert-not.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_ASSERT_NOT</span></tt></a>, <a class="refentry reference" href="./assert-msg.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_ASSERT_MSG</span></tt></a></p>
116<!-- modtime: November 10, 2004 04:45:16 +0000 -->
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