ptr_fun学习笔记
ptr_fun是将一个普通的函数适配成一个functor,添加上argument type和result type等类型， 其实现如下（例子里面是binary_function，unary_function同理)：template<class _Arg1,class _Arg2,class _Result> inlinepointer_to_binary_function<_Arg1, _Arg2, _Result,_Result(__fastcall *)(_Arg1, _Arg2)>ptr_fun(_Result (__fastcall *_Left)(_Arg1, _Arg2)){// return pointer_to_binary_function functor adapterreturn (std::pointer_to_binary_function<_Arg1, _Arg2, _Result,_Result (__fastcall *)(_Arg1, _Arg2)>(_Left));}
由上面的代码可见，ptr_fun只是将一个普通的函数（或者函数指针）适配成类pointer_to_binary_function，而该类实际上是binary_function的子类，这样出来的functor就有利于同STL的算法等适配。
下面的例子就是说明了使用ptr_fun将普通的函数适配成bind1st或bind2nd能够使用的functor，否则对bind1st或bind2nd直接绑定普通函数，则编译出错。
#include <algorithm>#include <functional>#include <iostream>using namespace std;int sum(int arg1, int arg2){cout<<"ARG 1: "<<arg1<<endl;cout<<"ARG 2: "<<arg2<<endl;int sum = arg1 + arg2;cout<<"SUM: "<<sum<<endl;return sum;}int main(int argc,char* argv[]){bind1st(ptr_fun(sum),1)(2); // the same as sum(1,2)bind2nd(ptr_fun(sum),1)(2); //the same as sum(2,1)getchar();return 0;}
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