Pointers and Memory

Function Pointers and Callbacks

A callback lets a general algorithm invoke caller-selected behavior without knowing its implementation.

What is Function Pointers and Callbacks?

A callback lets a general algorithm invoke caller-selected behavior without knowing its implementation.

Pass behavior into another function.

Important points

Every pointer must refer to a live compatible object or be null.
Pair each owned allocation with exactly one release.
Prefer clear ownership and const-correct interfaces.

C and C++ code examples

Run code →

main.c

#include <stdio.h>

int square(int value) { return value * value; }
int apply(int value, int (*operation)(int)) { return operation(value); }

int main(void) {
    printf("%d\n", apply(6, square));
    return 0;
}

Expected output

C++

Run code →

main.cpp

#include <functional>
#include <iostream>

int apply(int value, const std::function<int(int)>& operation) {
    return operation(value);
}

int main() {
    int factor = 6;
    std::cout << apply(factor, [](int value) { return value * value; }) << '\n';
}

Expected output

C and C++ comparison

C uses an explicit function-pointer type. C++ lambdas and std::function can hold richer callable objects, although a template is preferable in performance-sensitive generic code.

Ownership and cleanup are conventions enforced by the programmer.

C++

Containers and RAII types can encode ownership and cleanup in object lifetimes.

Practice exercises

Run both versions, then modify them to observe the different language guarantees.

Test null and allocation-failure paths.
Run with AddressSanitizer and UndefinedBehaviorSanitizer.
Document whether every pointer owns or only observes its object.