Pass a function pointer as an argument between classes

Question

How can we pass a function pointer as an argument? For example, the function pointer myFunPtr is an argument when calling class A and I need this pointer to point to function funcB in class B

 #include <iostream>


typedef void(*myFunPtr)(void);

class A {
public:
    A(myFunPtr ptr);
    virtual ~A();
    myFunPtr funptr;
};

A::A(myFunPtr ptr){
    std::cout << "Constructor A \n";
    funptr = ptr;
}

A::~A(){}

 
///////////////
class B {
public:
    B();
    virtual ~B();
    void funcB();
};

B::B(){
    std::cout << "Constructor B \n";
    A *objA = new A(funcB);
}

B::~B(){}

void B::funcB(){
    std::cout << " call B::funcB \n";
}

///////////////

int main(){
     B *objB = new B();
     delete objB;
        
    return 0;
}

Ted Lyngmo · Accepted Answer · 2020-11-03 15:42:25Z

4

This is a function pointer type to a free function (not a class member function):

typedef void(*myFunPtr)(void);

This is a B member function pointer type:

typedef void(B::*myFunPtr)(void);

Demo

Here's another Demo that will call a member function in a B. To do that, a pointer to a B and a pointer to a B member function is stored in A.

edited Nov 3, 2020 at 15:42

answered Nov 3, 2020 at 14:59

Ted Lyngmo

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7 Comments

MorningDewd Over a year ago

It should be noted that in order to call a member function pointer, an instance of the class is needed to invoke the function on, e.g. B b; (b.*ptr)(); or B b; std::invoke(ptr, b, args...);

DX-MON Over a year ago

I will also note that this typedef syntax is now deprecated in preference for using, and that in this case you could also use a std::function<void()> if you need less coupling between the two types.

Ted Lyngmo Over a year ago

@DX-MON Sure, I kept the same syntax as OP had to make the diff clear. I have the using syntax in the demo with a note.

AAAA Over a year ago

@Ted many thanks for the reply and the demo. Would it be possible to update the demo to call B::funcB? This is not called atm.

Ted Lyngmo Over a year ago

MohammedZiad I added a new demo. Note that I also added a pointer to a B in A like @MorningDewd mentioned.

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