Thread: Can I use std::bind to make function pointers instead of std::function objects ?

Code:

#include<functional>

typedef void (*foo)(int);
typedef std::function<void(int)> bar;

class X
{
public:
    void fun(int x){};
};

int main()
{
    X x;
    bar b=std::bind(&X::fun,&x,std::placeholders::_1); //This works
//     foo f=std::bind(&X::fun,&x,std::placeholders::_1); //This doesn't
}

But I need the to pass the function to a posix function (signal) defined to take function pointers of type foo.
Is there a way I can pass a member function (along with the object) to something defined to take function pointers only?

EDIT:
There turns out to be a member function of std::function that appears to do what I need, but after successfully compiling, promptly segfaults.

Code:

#include<functional>
#include<iostream>
typedef void (*foo)(int);
typedef std::function<void(int)> bar;

class X
{
public:
    X(int x):y(x){};
    void fun(int x){std::cout<<x<<y;};
private:
    int y;
};

int main()
{
    X x(4);
    bar b=std::bind(&X::fun,x,std::placeholders::_1);
    foo f=*b.target<foo>();
    f(5);
}

I know lambdas are convertible to function pointer if and only if they have no state. This makes sense, since a function pointer cannot store state. Likewise: a member function needs an instance. How are you going to encode that instance into a function pointer?
I don't know about std::bind and std::function, though.

The segfault problem is that foo is not the target type, and therefore target returns 0.

The target type is not a function pointer but the type specified by the result of bind. So you could do:

Code:

b.target<decltype( std::bind(&X::fun,x,std::placeholders::_1) )>()

But you can't put the result in a regular function pointer.