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    <p><strong>Update 2:</strong> Boost.Lambda makes this a piece of cake:</p> <pre><code>// headers #include &lt;boost/lambda/lambda.hpp&gt; #include &lt;boost/lambda/bind.hpp&gt; using namespace boost::lambda; // ... cout &lt;&lt; accumulate(dv.begin(), dv.end(), 0, _1 += bind(&amp;strange::value, _2)) //strange defined below &lt;&lt; endl; </code></pre> <p><strong>Update:</strong> This has been bugging me for a while. I can't just get any of the STL algorithms to work in a decent manner. So, I rolled my own:</p> <pre><code>// include whatever ... using namespace std; // custom accumulator that computes a result of the // form: result += object.method(); // all other members same as that of std::accumulate template &lt;class I, class V, class Fn1, class Fn2&gt; V accumulate2(I first, I last, V val, Fn1 op, Fn2 memfn) { for (; first != last; ++first) val = op(val, memfn(*first)); return val; } struct strange { strange(int a, int b) : _a(a), _b(b) {} int value() { return _a + 10 * _b; } int _a, _b; }; int main() { std::vector&lt;strange&gt; dv; dv.push_back(strange(1, 3)); dv.push_back(strange(4, 6)); dv.push_back(strange(20, -11)); cout &lt;&lt; accumulate2(dv.begin(), dv.end(), 0, std::plus&lt;int&gt;(), mem_fun_ref(&amp;strange::value)) &lt;&lt; endl; } </code></pre> <p>Of course, the original solution still holds: The easiest is to implement an <code>operator+</code>. In this case:</p> <pre><code>double operator+(double v, Object const&amp; x) { return v + x.a_; } </code></pre> <p>and make it a friend of <code>Object</code> or member (look up why you may prefer one over the other):</p> <pre><code>class Object { //... friend double operator+(double v, Object const&amp; x); </code></pre> <p>and you're done with:</p> <pre><code> result = accumulate(collection.begin(), collection.end(), 0.0); </code></pre> <p>My earlier approach doesn't work because we need a <code>binary_function</code>.</p> <p><a href="http://www.sgi.com/tech/stl/accumulate.html" rel="nofollow noreferrer">std::accumulate</a> manual.</p>
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    1. POusing of std::accumulate
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    1. USdirkgently
    1. USdirkgently
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      1. VTUpMod
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    1. COThanks for the manual. But your code won't compile.
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      1. USMykola Golubyev
    2. CO"result" is not initialized.
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      1. USMSalters
    3. COI think the third parameter to accumulate should be 0 not result. result has not yet been defined at that point.
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      1. USFerruccio
 

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