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9526044
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2012-03-01T23:51:17.197
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2012-03-01T23:56:38.303
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2012-03-01T23:56:38.303
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Credit goes to Mathias Gaunard on the boost.users mailing list for pointing me towards this solution: <pre><code> std::for_each(values.begin(), values.end(), boost::bind(boost::ref(avg), boost::bind(&value_wrapper_type::getValue, _1)) ); </code></pre> Wrapping <code>avg</code> with <code>boost::ref</code> is required because otherwise a copy of <code>avg</code> is filled out with the results of <code>getValue()</code>, rather than <code>avg</code> itself. Here is the full compiled and tested solution: <pre><code>#include <stdexcept> #include <vector> #include <algorithm> #include <iostream> #include <boost/bind.hpp> #include <boost/bind/mem_fn.hpp> // A value wrapper template<typename T> struct Value { Value(){} Value(const T& value, bool valid = true):m_value(value),m_valid(valid){} T getValue(){ return m_value; } bool getValid(){ return m_valid; } void setValue(const T& value){ m_value = value; } void setValid(const T& valid){ m_valid = valid; } private: T m_value; bool m_valid; }; // Class that calculates the average piecewise template<typename T> struct Average { private: T m_numPoints; T m_ChannelSum; public: typedef void result_type; Average() : m_numPoints(0), m_ChannelSum(0.0){} result_type operator()(T value){ m_numPoints++; m_ChannelSum+=value; } double getAverage(){ if (m_ChannelSum==0) { throw std::logic_error("Cannot get average of zero values"); } 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<value_type> value_wrapper_type; typedef std::vector<value_wrapper_type> 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<value_type> average_type; average_type avg; #if 0 // for loop version: for(value_vector_type::iterator it = values.begin(); it!=values.end(); it++){ avg(it->getValue()); // I want to put this in a for_each loop } #else // bind version: std::for_each(values.begin(), values.end(), boost::bind(boost::ref(avg), boost::bind(&value_wrapper_type::getValue, _1)) ); #endif std::cout << "Average: " << avg.getAverage() << " Count: " << avg.getCount() << " Sum: " << avg.getSum() << std::endl; } </code></pre>
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