Calling Member Function Pointers

Question

I am having trouble calling a function pointer inside a structure. I have used this approach before outside of classes, but now that I am trying it inside a class method using function pointers to other class methods.... I am receiving a compiler error. Here is my class:

class Myclass
{
    int i;

    void cmd1(int)
    {}

    void cmd2(int)
    {}

    void trans()
    {
        const struct
        {
            std::string cmd;
            void (Myclass::*func)(int)
        }
        CmdTable[] =
        {
            { "command1", &Myclass::cmd1 },
            { "command2", &Myclass::cmd2 }
        };

        CmdTable[0].func(i);
        CmdTable[1].func(i);
    }
};

The lines CmdTable[0].func(i); and CmdTable[1].func(i); both provide the following error: Error: expression must have (pointer-to-) function type.

I realize there are probably better ways of doing this, but I'm rather curious as to why what I've written doesn't work. Any explanation would be greatly appreciated.

You might want to read about [`std::function`](http://en.cppreference.com/w/cpp/utility/functional/function/function) and [`std::bind`](http://en.cppreference.com/w/cpp/utility/functional/function/bind). — Some programmer dude, Aug 22 '14 at 18:20
@JoachimPileborg: Why? Those are very heavy-weight, expensive "solutions" for a problem that doesn't need them. — Kerrek SB, Aug 22 '14 at 18:27

score 5 · Accepted Answer · answered Aug 22 '14 at 18:19

The pointer-to-member-function is a pure class property. You need to combine it with a class instance in order to make a meaningful function call. For example, to use the instance *this, you can use the operator ->* and say:

(this->*CmdTable[0])(i);

Or you can use operator .* on an object value:

(*this.*CmdTable[0])(i);

The latter form is always correct. For the former, note that operator->* may be overloaded and do something unrelated.

Calling Member Function Pointers

1 Answers1

Linked