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=UTF-8"> 5<title>Macro BOOST_PROTO_DEFINE_ENV_VAR</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="proto/reference.html#header.boost.proto.transform.env_hpp" title="Header <boost/proto/transform/env.hpp>"> 10<link rel="prev" href="boost/proto/_env/impl.html" title="Struct template impl"> 11<link rel="next" href="boost/proto/fold.html" title="Struct template fold"> 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="boost/proto/_env/impl.html"><img src="../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="proto/reference.html#header.boost.proto.transform.env_hpp"><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="boost/proto/fold.html"><img src="../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="refentry"> 27<a name="BOOST_PROTO_DEFINE_ENV_VAR"></a><div class="titlepage"></div> 28<div class="refnamediv"> 29<h2><span class="refentrytitle">Macro BOOST_PROTO_DEFINE_ENV_VAR</span></h2> 30<p>BOOST_PROTO_DEFINE_ENV_VAR — 31 Define a type and a global variable of that type that can be used 32 to initialize a slot in a Proto transform environment. 33 </p> 34</div> 35<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> 36<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>> 37 38</span>BOOST_PROTO_DEFINE_ENV_VAR(Type, Name)</pre></div> 39<div class="refsect1"> 40<a name="id-1.3.33.5.46.22.4"></a><h2>Description</h2> 41<p> 42 Proto primitive transforms can optionally accept an environment in 43 their third parameter which is a key/value store of environment 44 variables. Use the <code class="computeroutput">BOOST_PROTO_DEFINE_ENV_VAR()</code> macro 45 to define the keys. 46 </p> 47<p> 48 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> 49 for an example of the class interface created by this macro. 50 </p> 51<p> 52 <span class="bold"><strong>Example:</strong></span> 53 </p> 54<p> 55 </p> 56<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> 57 58<span class="keyword">struct</span> <span class="identifier">FetchMyKey</span> 59 <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> 60<span class="special">{</span><span class="special">}</span><span class="special">;</span> 61 62<span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="special">)</span> 63<span class="special">{</span> 64 <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> 65 <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> 66 <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> 67<span class="special">}</span></pre> 68<p> 69 </p> 70</div> 71</div> 72<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 73<td align="left"></td> 74<td align="right"><div class="copyright-footer">Copyright © 2008 Eric Niebler<p> 75 Distributed under the Boost Software License, Version 1.0. (See accompanying 76 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>) 77 </p> 78</div></td> 79</tr></table> 80<hr> 81<div class="spirit-nav"> 82<a accesskey="p" href="boost/proto/_env/impl.html"><img src="../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="proto/reference.html#header.boost.proto.transform.env_hpp"><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="boost/proto/fold.html"><img src="../../doc/src/images/next.png" alt="Next"></a> 83</div> 84</body> 85</html> 86
