Callbacks in C

A callback is any executable code that is passed as an argument to another code, which is expected to call back (execute) the argument at a given time. In simple language, If a reference of a function is passed to another function as an argument to call it, then it will be called a Callback function.

In C, a callback function is a function that is called through a function pointer.

Below is a simple example in C to illustrate the above definition to make it more clear.

C

// A simple C program to demonstrate callback
#include <stdio.h>

void A(){
  printf("I am function A\n");
}

// callback function
void B(void (*ptr)())
{
    (*ptr)(); // callback to A
}

int main()
{
    void (*ptr)() = &A;

    // calling function B and passing
    // address of the function A as argument
    B(ptr);

    return 0;
}

Output

I am function A

In C++ STL, functors are also used for this purpose.

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