Function Pointer/Callback Function

  • In C, a function pointer is a pointer that stores the address of a function. It can be used to invoke the function indirectly, through the function pointer. This can be useful in certain scenarios, such as when you want to pass a function as an argument to another function, or when you want to use a function as a callback.
  • Here’s an example of how to declare a function pointer in C:

int (*function_ptr)(int, int);

  • This declares a function pointer called function_ptr that points to a function that takes two int arguments and returns an int.
  • To assign a function to a function pointer, you can use the address-of operator &:

int add(int x, int y) {

return x + y;


function_ptr = &add;

  • To invoke the function through the function pointer, you can use the dereference operator *:

int result = (*function_ptr)(10, 20); // result = 30

  • Alternatively, you can use the function name without the dereference operator:

int result = function_ptr(10, 20); // result = 30

  • Function pointers can be passed as arguments to other functions, just like any other pointer type. For example:

void invoke_function(int (*func)(int, int)) {

int result = func(10, 20);

printf(“Result: %d\n”, result);


int main() {

invoke_function(&add); // prints “Result: 30”

return 0;


  • Function pointers can also be used as callback functions. For example, you can define a function that takes a function pointer as an argument and invokes the function when certain conditions are met.

void invoke_callback(int (*callback)(int), int x) {

if (x > 10) {




int main() {

void (*callback)(int) = &print_number;

invoke_callback(callback, 15); // prints “15”

return 0;


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