C++ Function Pointers

Introduce 4 ways to define function pointers in C++.

1. Traditional
2. typedef
3. using
4. std::function

1. Traditional

Syntax

return_type (*pointer_name)(parameter_types1, parameter_types2);

// example
int (*funcPtr)(int, int);

2. typedef

Syntax

typedef return_type (*pointer_name)(parameter_types1, parameter_types2);

// example
typedef int (*funcPtr)(int, int);

funcPtr becomes an alias for the type “pointer to a function that takes two int parameters and returns an int”.

3. using

Syntax

using pointer_name = return_type (*)(parameter_types1, parameter_types2);

// example
using funcPtr = int (*)(int, int)

funcPtr becomes an alias for the type “pointer to a function that takes two int parameters and returns an int”.

4. std::function

Syntax

std::function<return_type(parameter_types1, parameter_types2)> pointer_name;

// example
std::function<int(int, int)> funcPtr;

5. Example

#include <iostream>
#include <functional>

int add(int a, int b) {
    return a + b;
}

int main() {
    // 1. traditional
    int (*funcPtr1)(int, int);
    funcPtr1 = add;
    std::cout << funcPtr1(1, 2) << '\n';

    // 2. typedef
    typedef int (*AddFunc_typedef)(int, int);
    AddFunc_typedef funcPtr2 = add;
    std::cout << funcPtr2(1, 2) << '\n';

    // 3. using
    using AddFunc_using = int (*)(int, int);
    AddFunc_using funcPtr3 = add;
    std::cout << funcPtr3(1, 2) << '\n';

    // 4. std::function
    std::function<int(int, int)> funcPtr4 = add;
    std::cout << funcPtr4(1, 2) << '\n';

    return 0;
}