Passing a pointer to a class member function as a parameter - c++

Question

I have written a small program where I am trying to pass a pointer to member function of a class to another function. Can you please help me and where I am going wrong..?
#include<iostream>
using namespace std;
class test{
public:
typedef void (*callback_func_ptr)();
callback_func_ptr cb_func;
void get_pc();
void set_cb_ptr(void * ptr);
void call_cb_func();
};
void test::get_pc(){
cout << "PC" << endl;
}
void test::set_cb_ptr( void *ptr){
cb_func = (test::callback_func_ptr)ptr;
}
void test::call_cb_func(){
cb_func();
}
int main(){
test t1;
t1.set_cb_ptr((void *)(&t1.get_pc));
return 0;
}
I get the following error when I try to compile it.
error C2276: '&' : illegal operation on bound member function expression

Answer 1

You cannot cast a function pointer to void*.
If you want a function pointer to point to a member function you must declare the type as
ReturnType (ClassType::*)(ParameterTypes...)
Further you cannot declare a function pointer to a bound member function, e.g.
func_ptr p = &t1.get_pc // Error
Instead you must get the address like this:
func_ptr p = &test::get_pc // Ok, using class scope.
Finally, when you make a call to a function pointer pointing to a member function, you must call it with an instance of the class that the function is a member of. For instance:
(this->*cb_func)(); // Call function via pointer to current instance.
Here's the full example with all changes applied:
#include <iostream>
class test {
public:
typedef void (test::*callback_func_ptr)();
callback_func_ptr cb_func;
void get_pc();
void set_cb_ptr(callback_func_ptr ptr);
void call_cb_func();
};
void test::get_pc() {
std::cout << "PC" << std::endl;
}
void test::set_cb_ptr(callback_func_ptr ptr) {
cb_func = ptr;
}
void test::call_cb_func() {
(this->*cb_func)();
}
int main() {
test t1;
t1.set_cb_ptr(&test::get_pc);
t1.call_cb_func();
}

Answer 2

In addition to Snps's answer, you could also use a function wrapper from C++11 to store a lambda function:
#include <iostream>
#include <functional>
class test
{
public:
std::function<void ()> Func;
void get_pc();
void call_cb_func();
void set_func(std::function<void ()> func);
};
void test::get_pc()
{
std::cout << "PC" << std::endl;
}
void test::call_cb_func()
{
Func();
}
void test::set_func(std::function<void ()> func)
{
Func = func;
}
int main() {
test t1;
t1.set_func([&](){ t1.get_pc(); });
t1.call_cb_func();
}