So the function pointers can be used to simplify code by providing a simple way to select a function to execute based on run-time values. Function pointers do always point to a function having a specific signature. Thus, all functions used with the same function pointer must have the same parameters and return type

Syntax:

ReturnType (*PtrToFun)(arguments if any)

Example:

#include "stdio.h"
void my_int_func(int x)
{
    printf( "%d\n", x );
}

int main()
{
    void (*foo)(int);
    /* the ampersand is actually optional */
    foo = &my_int_func;
    foo(10);
    return 0;
}

In above example function pointer foo is used to call the function my_int_func.

Uses of Function Pointers

Pointer to function is useful when you want to choose a function dynamically at run time – usually based on certain conditions. Function Pointers are used to implement generic functions like qsort(), callbacks, state machines and anywhere else run time binding of a function is required. Also Function pointers are used to store interrupt handlers in tables.

To begin, check out the qsort fucntion

void qsort(void *base, size_t nmemb, size_t size, 
           int (*compar)(const void *, const void *));

Here, you need to pass a pointer to the function that compares the objects that you are sorting. Since qsort() is a generic implementation and does not care what you are sorting, it is up to you to implement a funtion which compares the objects that you are sorting and pass it on to qsort(). qsort() just invokes your compare function by dereferencing the function pointer.

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