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| <h2><span class="refentrytitle">Macro BOOST_PROTO_DEFINE_ENV_VAR</span></h2> |
| <p>BOOST_PROTO_DEFINE_ENV_VAR — |
| Define a type and a global variable of that type that can be used |
| to initialize a slot in a Proto transform environment. |
| </p> |
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| <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> |
| <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="proto/reference.html#header.boost.proto.transform.env_hpp" title="Header <boost/proto/transform/env.hpp>">boost/proto/transform/env.hpp</a>> |
| |
| </span>BOOST_PROTO_DEFINE_ENV_VAR(Type, Name)</pre></div> |
| <div class="refsect1"> |
| <a name="idp382527664"></a><h2>Description</h2> |
| <p> |
| Proto primitive transforms can optionally accept an environment in |
| their third parameter which is a key/value store of environment |
| variables. Use the <code class="computeroutput">BOOST_PROTO_DEFINE_ENV_VAR()</code> macro |
| to define the keys. |
| </p> |
| <p> |
| See the description for <code class="computeroutput"><a class="link" href="boost/proto/data_type.html" title="Struct data_type">proto::data_type</a></code> |
| for an example of the class interface created by this macro. |
| </p> |
| <p> |
| <span class="bold"><strong>Example:</strong></span> |
| </p> |
| <p> |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_PROTO_DEFINE_ENV_VAR</span><span class="special">(</span><span class="identifier">mykey_type</span><span class="special">,</span> <span class="identifier">mykey</span><span class="special">)</span><span class="special">;</span> |
| |
| <span class="keyword">struct</span> <span class="identifier">FetchMyKey</span> |
| <span class="special">:</span> <a class="link" href="boost/proto/when.html" title="Struct template when">proto::when</a><span class="special"><</span> <a class="link" href="boost/proto/_.html" title="Struct _">_</a><span class="special">,</span> <a class="link" href="boost/proto/_env_var.html" title="Struct template _env_var">proto::_env_var</a><span class="special"><</span><span class="identifier">mykey_type</span><span class="special">></span> <span class="special">></span> |
| <span class="special">{</span><span class="special">}</span><span class="special">;</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="special">)</span> |
| <span class="special">{</span> |
| <a class="link" href="boost/proto/terminal.html" title="Struct template terminal">proto::terminal</a><span class="special"><</span><span class="keyword">int</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">{</span><span class="number">42</span><span class="special">}</span><span class="special">;</span> |
| <span class="keyword">char</span> <span class="keyword">const</span> <span class="special">*</span> <span class="identifier">sz</span> <span class="special">=</span> <span class="identifier">FetchMyKey</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="number">0</span><span class="special">,</span> <span class="special">(</span><span class="identifier">mykey</span> <span class="special">=</span> <span class="string">"hello!"</span><span class="special">)</span><span class="special">)</span><span class="special">;</span> |
| <span class="identifier">assert</span><span class="special">(</span><span class="number">0</span> <span class="special">==</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">strcmp</span><span class="special">(</span><span class="identifier">sz</span><span class="special">,</span> <span class="string">"hello!"</span><span class="special">)</span><span class="special">;</span> |
| <span class="special">}</span></pre> |
| <p> |
| </p> |
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| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2008 Eric Niebler<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>) |
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