ptr_fun

头文件：<functional>

ptr_fun是将一个普通的函数适配成一个仿函数(functor), 添加上argument_type和result type等类型，它的定义如下：

 template<class _Arg1,
     class _Arg2,
     class _Result> inline
     pointer_to_binary_function<_Arg1, _Arg2, _Result,
         _Result(__clrcall *)(_Arg1, _Arg2)>
             ptr_fun(_Result (__clrcall *_Left)(_Arg1, _Arg2))
     {    // return pointer_to_binary_function functor adapter
     return (pointer_to_binary_function<_Arg1, _Arg2, _Result,
         _Result (__clrcall *)(_Arg1, _Arg2)>(_Left));
     }

下面的例子就是说明了使用ptr_fun将普通函数(两个参数, 如果有多个参数, 要改用boost::bind)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)
 {
     std::cout<< "arg1 = " << arg1 << std::endl;
     std::cout<< "arg2 = " << arg2 << std::endl;

     int sum = arg1 + arg2;
     std::cout << "sum = " << sum << std::endl;

     return sum;
 }

 int main(int argc, char *argv[], char *env[])
 {
     bind1st(ptr_fun(sum), 1)(2);        // the same as sum(1,2)
     bind2nd(ptr_fun(sum), 1)(2);        // the same as sum(2,1)

     return 0;
 }