Callbacks

Callbacks or callback functions are references that are passed as arguments to a piece of code, which will execute whenever an event associated with the callback function occurs.

The function will be executed externally by an API.

Generally it is used to call a higher level subroutine from a lower-level software like the operating system.

Examples

• Windows API - e.g. WaveOutProc()
• In JavaScript, they are functions passed as arguments to other functions, for calling other functions from a function
• A pseudocode example:

  funct printANumber(int n, callback callbackFunction) {
      printout("Printing" + n);
  }
  funct printFinishMessage(){
      printout("Finished printing.");
  }
  funct main() {
      printANumber(6, printFinishMessage);
  }
  

  The output will be:

  Printing 6
  Finished printing