What is the usage of function pointers in the C language?

2 years ago
Benjamin Taylor
2 minutes

– Function pointers in C are variables that point to functions, allowing them to point to the starting address of a function. There are two main uses for function pointers.

  1. Function pointers as parameters: Function pointers can be used as parameters in a function, to pass the address of a function during a function call, allowing for calling other functions within the function. This can enable advanced function capabilities, such as callback functions. For example:
#include <stdio.h>

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

void iterate(int start, int end, void(*func)(int)) {
    for(int i = start; i <= end; i++) {
        func(i);
    }
}

int main() {
    iterate(1, 5, print);
    
    return 0;
}
  1. Function pointers as return values: Function pointers can also be used as return values, to return a pointer to a function. This allows for the ability to return different function addresses based on different conditions. For example:
#include <stdio.h>

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

int subtract(int a, int b) {
    return a - b;
}

int multiply(int a, int b) {
    return a * b;
}

int divide(int a, int b) {
    return a / b;
}

int (*getOperation(char op))(int, int) {
    switch(op) {
        case '+':
            return add;
        case '-':
            return subtract;
        case '*':
            return multiply;
        case '/':
            return divide;
        default:
            return NULL;
    }
}

int main() {
    int a = 10, b = 5;
    char op = '+';
    
    int (*operation)(int, int) = getOperation(op);
    
    if(operation != NULL) {
        int result = operation(a, b);
        printf("%d\n", result);
    } else {
        printf("Invalid operator\n");
    }
    
    return 0;
}

Therefore, depending on the different operators, the corresponding function address can be returned, enabling different operations to be carried out.

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