ashur ashur -4 years ago 80
C++ Question

C++: Calling member function via pointer

I have this example code of using pointer to member function, which I want to change during runtime, but I cannot make it work. I've already tried

(*this)._currentPtr(4, 5)
. What is the proper way of calling pointer to method inside same class ?

The error : expression must have (pointer-to-) function type

#include <iostream>
#include <cstdlib>

class A {


void setPtr(int v);
void useFoo();

typedef int (A::*fooPtr)(int a, int b);

fooPtr _currentPtr;

int foo1(int a, int b);
int foo2(int a, int b);

void A::setPtr(int v){
if(v == 1){
_currentPtr = foo1;
} else {
_currentPtr = foo2;

void A::useFoo(){

//std::cout << this->*_currentPtr(4,5); // ERROR

int A::foo1(int a, int b){
return a - b;

int A::foo2(int a, int b){
return a + b;

int main(){

A obj;


return 0;

Answer Source

You need to tell the compiler which class the foos are coming from (otherwise it thinks they're functions from global scope):

void A::setPtr(int v){
    if(v == 1){
        _currentPtr = &A::foo1;
                  //  ^^^^
    } else {
        _currentPtr = &A::foo2;
                  //  ^^^^

and you need a set of parentheses here:

std::cout << (this->*_currentPtr)(4,5);
          // ^                  ^
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