std::function with non-static member functions
c++, visual-studio-2010, winapi
Solution
I think the problem you are having is that a member function requires not only a function pointer, but a pointer to the calling object. In other words, member functions have an additional implicit argument that is the pointer to the calling object.
To set a member function to a std::function, you need to use std::bind like this:
std::function<void(int)> testFunc(std::bind(&A::func, this, _1));
This binds the this pointer of the current A instance to the function so it has the function pointer and the object instance, which is enough information to properly call the function. The _1 argument indicates that the first explicit argument will be provided when the function is called.
Problem
i'm trying to understand a concept and an error. what's wrong with this? ``` class A { public: A() { std::function<void(int)> testFunc(&A::func); } private: void func(int) {} } ``` my question, is it possible to create any sort of object that is able to call a member of a specific instance where std::function acts like a member function pointer, except without the wacky type definition that can't be used as function parameters in inheriting classes. for example: ``` class A { public: A() { index[WM_CREATE] = &A::close; index[WM_DESTROY] = &A::destroy; } protected: map<UINT msg, void (A::*)(HWND, UINT , WPARAM, LPARAM)> index; void close(HWND,UINT, WPARAM, LPARAM); void destroy(HWND, UINT, WPARAM, LPARAM); }; class B : public A { public: B() { index[WM_CREATE] = &B::create; // error because it's not a pointer of type A::* } private: void create(HWND, UINT, WPARAM, LPARAM); }; ``` I'm thinking i'm on the right track of using std::functions like so: ``` class A { public: // Gigantic stl error with these two A() // | { // V index[WM_CREATE] = std::function<void(HWND, UINT, WPARAM, LPARAM>(&A::close); index[WM_DESTROY] = std::function<void(HWND, UINT, WPARAM, LPARAM>(&A::destroy); } protected: map<UINT msg, std::function<void(HWND, UINT, WPARAM, LPARAM)> > index; void close(HWND,UINT, WPARAM, LPARAM); void destroy(HWND, UINT, WPARAM, LPARAM); }; class B : public A { public: // and this one B() // | { // V index[WM_CREATE] = std::function<void(HWND, UINT, WPARAM, LPARAM)>(&B::create); } private: void create(HWND, UINT, WPARAM, LPARAM); }; ``` if someone could explain what these giant cryptic errors mean and how to fix them, i would greatly appreciate it.