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    copied!<p>Since <code>u</code> is a vector of <code>std::pair&lt;double, std::string&gt;</code>, you will want to have the corresponding comparison function called. Since the name alone is not sufficient, you will have to dismabiguate it for the compiler by casting it to a pointer with the right function pointer type. In your case it is a function that takes two const references to the pair type and returns a bool - so the function pointer type you have to cast to is exactly that:</p> <pre><code>bool (*)(const std::pair&lt;int, int&gt; &amp;, const std::pair&lt;int, int&gt; &amp;) </code></pre> <p>Together that makes a pretty ugly cast:</p> <pre><code>std::sort(u.begin(), u.end(), static_cast&lt;bool (*)(const std::pair&lt;int, int&gt; &amp;, const std::pair&lt;int, int&gt; &amp;)&gt;(&amp;Misc::sortPair)); </code></pre> <p>Whoa.</p> <p>Better use some typedefs to clarify what you are doing:</p> <pre><code>//includes as they were... typedef std::pair&lt;double, std::string&gt; dsPair; //or something more meaningful class Misc { public: //Comment out the next three lines to compile without problems static bool sortPair(const std::pair&lt;int, int&gt; &amp;a, const std::pair&lt;int, int&gt; &amp;b){ return a.first &lt; b.first; } static bool sortPair(dsPair const&amp; a, dsPair const&amp; b){ return a.first &lt; b.first; } }; int main () { std::vector&lt;dsPair&gt; u{ {10.0, "ten"}, {5.0, "five"}, {1.0, "one"} }; /** the function pointer typedef * It takes a bit getting used to, but no worries, * you won't have to do it THAT often: **/ typedef bool(*dsPairCompFunc)(dsPair const&amp;, dsPair const&amp;); //and now the cast is much clearer: std::sort(begin(u), end(u), static_cast&lt;dsPairCompFunc&gt;(&amp;Misc::sortPair)); for (auto&amp; e : u){ std::cout &lt;&lt; e.first &lt;&lt; "\n"; } return 0; } </code></pre> <p>I changed some of the old C++03 stuff to C++11 in case your compiler supports it.</p>
 

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