Question

I try to get this code running. I am almost there but I got stuck with the line:

 _f = std::bind1st(
         std::mem_fun(f, x);

First of all please understand that I don’t want to change any code, but the constructor. Why? Because I want to learn. Eventually I want to write a wrapper class Func, that can handle free functions and member function at the same time, in this very manner.

So what wuld I have to put as the first argument inside the std::mem_func()-call???
I tried numerous things.

Probably this is a duplicate, but I don’t know how to search for this problem. I lack the vocabulary. If someone can point to a tutorial or something, that would help me to express this problem, I would also appreciate it.

Here is the full sample code:

#include <boost/function.hpp>
#include <iostream>

struct X
{
    int foo(int i)
    {
        return i;
    };
};

class Func
{

public:

   Func(X *x,  int (X::* f) (int))
   {
      _f = std::bind1st(
         std::mem_fun(f, x);

      std::cout << _f(5); // Call x.foo(5)
   };

private:

    boost::function<int (int)> _f;
};

int main()
{

    X x;

    Func func(&x, &X::foo);
    return 0;
}

Thanks in advance.

Answer 1

It seems you just forgot a paren:

_f = std::bind1st(std::mem_fun(f), x);

Although I would initialize with

Func(X *x,  int (X::* f) (int))
  : _f(std::bind1st(std::mem_fun(f), x))
{
    std::cout << _f(5); // Call x.foo(5)
};

(It doesn’t matter in this case, but this style is safer in the long run.)