Function pointer to member function

Question

I'd like to set up a function pointer as a member of a class that is a pointer to another function in the same class. The reasons why I'm doing this are complicated.

In this example, I would like the output to be "1"

class A { public:  int f();  int (*x)(); }  int A::f() {  return 1; }   int main() {  A a;  a.x = a.f;  printf("%d\n",a.x()) } 

But this fails at compiling. Why?

Answer 1

The syntax is wrong. A member pointer is a different type category from a ordinary pointer. The member pointer will have to be used together with an object of its class:

class A { public:  int f();  int (A::*x)(); // <- declare by saying what class it is a pointer to };  int A::f() {  return 1; }   int main() {  A a;  a.x = &A::f; // use the :: syntax  printf("%d\n",(a.*(a.x))()); // use together with an object of its class } 

a.x does not yet say on what object the function is to be called on. It just says that you want to use the pointer stored in the object a. Prepending a another time as the left operand to the .* operator will tell the compiler on what object to call the function on.

Answer 2

int (*x)() is not a pointer to member function. A pointer to member function is written like this: int (A::*x)(void) = &A::f;.