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170 lines
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<title>Function Output Iterator Adaptor Documentation</title>
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<img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align=
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"center" width="277" height="86">
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<h1>Function Output Iterator Adaptor</h1>
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Defined in header <a href=
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"../../boost/function_output_iterator.hpp">boost/function_output_iterator.hpp</a>
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<p>The function output iterator adaptor makes it easier to create
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custom output iterators. The adaptor takes a <a
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href="http://www.sgi.com/tech/stl/UnaryFunction.html">Unary
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Function</a> and creates a model of <a
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href="http://www.sgi.com/tech/stl/OutputIterator.html">Output
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Iterator</a>. Each item assigned to the output iterator is passed
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as an argument to the unary function. The motivation for this
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iterator is that creating a C++ Standard conforming output
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iterator is non-trivial, particularly because the proper
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implementation usually requires a proxy object. On the other hand,
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creating a function (or function object) is much simpler.
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<h2>Synopsis</h2>
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<blockquote>
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<pre>
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namespace boost {
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template <class UnaryFunction>
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class function_output_iterator;
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template <class UnaryFunction>
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function_output_iterator<UnaryFunction>
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make_function_output_iterator(const UnaryFunction& f = UnaryFunction())
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}
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</pre>
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</blockquote>
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<h3>Example</h3>
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In this example we create an output iterator that appends
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each item onto the end of a string, using the <tt>string_appender</tt>
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function.
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<blockquote>
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<pre>
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#include <iostream>
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#include <string>
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#include <vector>
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#include <boost/function_output_iterator.hpp>
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struct string_appender {
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string_appender(std::string& s) : m_str(s) { }
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void operator()(const std::string& x) const {
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m_str += x;
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}
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std::string& m_str;
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};
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int main(int, char*[])
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{
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std::vector<std::string> x;
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x.push_back("hello");
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x.push_back(" ");
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x.push_back("world");
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x.push_back("!");
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std::string s = "";
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std::copy(x.begin(), x.end(),
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boost::make_function_output_iterator(string_appender(s)));
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std::cout << s << std::endl;
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return 0;
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}
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</pre>
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</blockquote>
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<hr>
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<h2><a name="function_output_iterator">The Function Output Iterator Class</a></h2>
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<blockquote>
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<pre>
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template <class UnaryFunction>
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class function_output_iterator;
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</pre>
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</blockquote>
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The <tt>function_output_iterator</tt> class creates an <a
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href="http://www.sgi.com/tech/stl/OutputIterator.html">Output
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Iterator</a> out of a
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<a href="http://www.sgi.com/tech/stl/UnaryFunction.html">Unary
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Function</a>. Each item assigned to the output iterator is passed
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as an argument to the unary function.
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<h3>Template Parameters</h3>
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<table border>
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<tr>
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<th>Parameter
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<th>Description
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<tr>
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<td><tt>UnaryFunction</tt>
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<td>The function type being wrapped. The return type of the
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function is not used, so it can be <tt>void</tt>. The
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function must be a model of <a
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href="http://www.sgi.com/tech/stl/UnaryFunction.html">Unary
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Function</a>.</td>
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</table>
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<h3>Concept Model</h3>
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The function output iterator class is a model of <a
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href="http://www.sgi.com/tech/stl/OutputIterator.html">Output
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Iterator</a>.
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<h2>Members</h3>
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The function output iterator implements the member functions
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and operators required of the <a
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href="http://www.sgi.com/tech/stl/OutputIterator.html">Output
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Iterator</a> concept. In addition it has the following constructor:
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<pre>
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explicit function_output_iterator(const UnaryFunction& f = UnaryFunction())
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</pre>
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<br>
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<br>
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<hr>
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<h2><a name="make_function_output_iterator">The Function Output Iterator Object
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Generator</a></h2>
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The <tt>make_function_output_iterator()</tt> function provides a
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more convenient way to create function output iterator objects. The
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function saves the user the trouble of explicitly writing out the
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iterator types. If the default argument is used, the function
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type must be provided as an explicit template argument.
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<blockquote>
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<pre>
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template <class UnaryFunction>
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function_output_iterator<UnaryFunction>
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make_function_output_iterator(const UnaryFunction& f = UnaryFunction())
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</pre>
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</blockquote>
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<hr>
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<p>© Copyright Jeremy Siek 2001. Permission to copy, use,
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modify, sell and distribute this document is granted provided this
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copyright notice appears in all copies. This document is provided
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"as is" without express or implied warranty, and with no claim as
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to its suitability for any purpose.
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