Passing Functions as Parameters in C and C++

In programming, it’s often necessary to pass functions as parameters to other functions. This technique allows for more flexibility and generic code. In this tutorial, we’ll explore how to pass functions as parameters in both C and C++.

Introduction to Function Pointers

To understand how to pass functions as parameters, you need to know about function pointers. A function pointer is a variable that holds the memory address of a function. You can declare a function pointer using the following syntax:

void (*funcPtr)(int);

This declares a function pointer funcPtr that points to a function taking an int parameter and returning void.

Passing Functions as Parameters in C

In C, you can pass functions as parameters by declaring a function pointer as a parameter. Here’s an example:

void func(void (*f)(int)) {
    for (int i = 0; i < 5; i++) {
        (*f)(i);
    }
}

void print(int x) {
    printf("%d\n", x);
}

int main() {
    func(print);
    return 0;
}

In this example, the func function takes a function pointer f as a parameter. The print function is passed to func, which calls it five times with different arguments.

Typedef for Function Pointers

Using raw function pointers can be messy and error-prone. To make your code more readable, you can use typedef to define a new type for the function pointer:

typedef void (*FunctionType)(int);

void func(FunctionType f) {
    // ...
}

void print(int x) {
    printf("%d\n", x);
}

int main() {
    func(print);
    return 0;
}

This makes your code more readable and easier to maintain.

Passing Functions as Parameters in C++

In C++, you can use the std::function class from the <functional> library to pass functions as parameters. Here’s an example:

#include <functional>
#include <iostream>

void func(std::function<void(int)> f) {
    for (int i = 0; i < 5; i++) {
        f(i);
    }
}

void print(int x) {
    std::cout << x << std::endl;
}

int main() {
    func(print);
    return 0;
}

This code uses the std::function class to declare a function pointer that takes an int parameter and returns void. The print function is passed to func, which calls it five times with different arguments.

Using Templates for Function Parameters

Another way to pass functions as parameters in C++ is by using templates. Here’s an example:

template <typename Func>
void func(Func f) {
    for (int i = 0; i < 5; i++) {
        f(i);
    }
}

void print(int x) {
    std::cout << x << std::endl;
}

int main() {
    func(print);
    return 0;
}

This code uses a template parameter Func to declare a function pointer. The print function is passed to func, which calls it five times with different arguments.

Conclusion

Passing functions as parameters is a powerful technique that allows for more flexibility and generic code. In this tutorial, we’ve explored how to pass functions as parameters in both C and C++ using function pointers, typedef, std::function, and templates. By mastering these techniques, you’ll be able to write more efficient and reusable code.