Pointer to functions

Function Pointers in C

One of the powerful features of C is the ability to define pointers to functions.

• A function pointer is a variable that stores the address of a function.

• Like other pointers, function pointers can be declared, assigned, and used to call the function they point to.

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Declaring Function Pointers

The general syntax for declaring a function pointer is:

return_type (*function_pointer_name)(argument_type1, argument_type2, ...);

Example:

int (*fp)(float, char);

• fp is a function pointer that points to a function taking one float and one char argument and returns an int.

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Initializing Function Pointers

• Function pointers must be initialized before use.

• Assign the function’s name (without parentheses) to the pointer:

fptr = add; // assigns address of function add to fptr

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Example: Using Function Pointers

#include <stdio.h>

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

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

int main() {
    int (*fptr)(int, int);  // declare function pointer

    fptr = add;             // point to add function
    printf("%d\n", fptr(2, 3)); // calls add(2,3)

    fptr = sub;             // point to sub function
    printf("%d", fptr(3, 2));   // calls sub(3,2)

    return 0;
}

Output:

5
1

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Key Points:

1. Function pointers allow dynamic selection of functions at runtime.

2. Useful for implementing callback functions and table-driven programs.

3. Can point to any function with a matching signature (return type and parameters).