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POIterating over the output of a member function in std::for_each
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  1. POIterating over the output of a member function in std::for_each
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    copied!<p>I have a class with an accessor member function that I want to call and apply the result to a functor using std::for_each. I have a working version below that uses a for loop and for_each, but the for_each version is cryptic and cumbersome. Is there a way I can make the for_each version more concise, considering I have access to boost, but not C++11?</p> <pre><code>#if 0 // for loop version: for(value_vector_type::iterator it = values.begin(); it!=values.end(); it++){ avg(it-&gt;getValue()); // I want to put this in a for_each loop } #else // bind version: std::for_each(values.begin(), values.end(), // iterate over all values boost::bind( boost::mem_fn(&amp;average_type::operator()), // attach the averaging functor to the output of the getvalue call &amp;avg, boost::bind( boost::mem_fn(&amp;value_wrapper_type::getValue), // bind the getValue call to each element in values _1 ) ) ); #endif </code></pre> <p>Here is the full working implementation:</p> <pre><code>#include &lt;vector&gt; #include &lt;algorithm&gt; #include &lt;iostream&gt; #include &lt;boost/bind.hpp&gt; #include &lt;boost/bind/mem_fn.hpp&gt; // A value wrapper template&lt;typename T&gt; struct Value { Value(){} Value(const T&amp; value, bool valid = true):m_value(value),m_valid(valid){} T getValue(){ return m_value; } bool getValid(){ return m_valid; } void setValue(const T&amp; value){ m_value = value; } void setValid(const T&amp; valid){ m_valid = valid; } private: T m_value; bool m_valid; }; // Class that calculates the average piecewise template&lt;typename T&gt; struct Average { private: T m_numPoints; T m_ChannelSum; public: Average() : m_numPoints(0), m_ChannelSum(0.0){} void operator()(T value){ m_numPoints++; m_ChannelSum+=value; } double getAverage(){ return m_ChannelSum/m_numPoints; } T getCount(){ return m_numPoints; } T getSum(){ return m_ChannelSum; } }; // Run the average computation on several values int main(int argc, char** argv){ typedef int value_type; typedef Value&lt;value_type&gt; value_wrapper_type; typedef std::vector&lt;value_wrapper_type&gt; value_vector_type; value_vector_type values; values.push_back(value_wrapper_type(5)); values.push_back(value_wrapper_type(7)); values.push_back(value_wrapper_type(3)); values.push_back(value_wrapper_type(1)); values.push_back(value_wrapper_type(2)); typedef Average&lt;value_type&gt; average_type; average_type avg; #if 0 // for loop version: for(value_vector_type::iterator it = values.begin(); it!=values.end(); it++){ avg(it-&gt;getValue()); // I want to put this in a for_each loop } #else // bind version: std::for_each(values.begin(), values.end(), // iterate over all values boost::bind( boost::mem_fn(&amp;average_type::operator()), // attach the averaging functor to the output of the getvalue call &amp;avg, boost::bind( boost::mem_fn(&amp;value_wrapper_type::getValue), // bind the getValue call to each element in values _1 ) ) ); #endif std::cout &lt;&lt; "Average: " &lt;&lt; avg.getAverage() &lt;&lt; " Count: " &lt;&lt; avg.getCount() &lt;&lt; " Sum: " &lt;&lt; avg.getSum() &lt;&lt; std::endl; } </code></pre> <p>note: my original question was how to construct a for_each at all, but I've found that solution and a whole new question did not make much sense.</p> <p>Thanks, all help is really appreciated!</p>
 

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