C++ Callback Function Pointer Example

5 min read Jul 01, 2024

C++ Callback Function Pointer Example

Callback functions are powerful tools in C++ programming, allowing you to pass functions as arguments to other functions, enabling dynamic and flexible code execution. This article will provide a comprehensive explanation of callback functions with a clear example.

Understanding Callback Functions

In essence, a callback function is a function that is passed as an argument to another function. This "host" function then calls the callback function at some point during its execution, allowing the callback to perform specific actions based on the context. This mechanism promotes modularity and flexibility, enabling you to tailor the behavior of the host function dynamically.

The Power of Function Pointers

The foundation of callback functions lies in function pointers. In C++, you can declare a variable that holds the memory address of a function, just like you would store the address of any other data type. This allows you to pass functions as arguments to other functions.

Example: Sorting with a Callback

Let's illustrate the concept with a practical example. Imagine we have a simple sorting algorithm that needs to compare elements in an array. Instead of hardcoding the comparison logic within the sorting function, we can make it more flexible by using a callback function:

#include 

// Function prototype for the callback function
typedef bool (*compare_function)(int, int);

// Sorting function using a callback function
void sort(int arr[], int n, compare_function compare) {
    for (int i = 0; i < n - 1; i++) {
        for (int j = i + 1; j < n; j++) {
            if (compare(arr[i], arr[j])) {
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
    }
}

// Example compare functions for ascending and descending order
bool ascending_order(int a, int b) {
    return a > b; 
}

bool descending_order(int a, int b) {
    return a < b;
}

int main() {
    int arr[] = {5, 2, 9, 1, 7};
    int n = sizeof(arr) / sizeof(arr[0]);

    // Sort in ascending order
    sort(arr, n, ascending_order); 
    std::cout << "Ascending Order: ";
    for (int i = 0; i < n; i++) {
        std::cout << arr[i] << " ";
    }
    std::cout << std::endl;

    // Sort in descending order
    sort(arr, n, descending_order);
    std::cout << "Descending Order: ";
    for (int i = 0; i < n; i++) {
        std::cout << arr[i] << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation:

compare_function: This typedef defines a function pointer type that points to a function taking two integers as arguments and returning a boolean value.
sort Function: This function takes an array, its size, and a function pointer compare as arguments.
ascending_order & descending_order: These are simple comparison functions defining the criteria for the sorting algorithm.
main Function:
- The code first sorts the array in ascending order by passing the ascending_order function pointer to sort.
- Then, it sorts the array again in descending order using the descending_order function pointer.

Conclusion

Callback functions are a valuable technique in C++ programming, offering a powerful way to dynamically alter the behavior of functions. By utilizing function pointers, you can inject custom logic into functions, leading to more adaptable and flexible code. The example demonstrates how callbacks can be used for sorting, but their applications extend to various other scenarios, such as event handling, asynchronous operations, and more.

C++ Callback Function Pointer Example