Function Pointers and Callbacks

Function Pointers and Callbacks

Just like variables, functions have addresses. A function pointer stores one; passing it to another function creates a callback.

Storing a function's address

#include <stdio.h>

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

int main() {
    int (*op)(int, int) = add;   // op points to add
    printf("%d\n", op(5, 3));   // 8
    op = sub;
    printf("%d\n", op(5, 3));   // 2
    return 0;
}

The syntax

int (*op)(int, int) reads: a pointer to a function taking two ints and returning int.

Callbacks

Passing a function pointer into another function lets it "call back" into your code:

void apply(int (*f)(int), int x) {
    printf("%d\n", f(x));
}

Real uses

• Sorting with custom comparators.
• Event handlers and menus.
• Generic library hooks.

TL;DR

• A function pointer stores a function's address.
• Declare: int (*op)(params).
• Call through it like a normal function.
• Callbacks = passing a function to another function.