user defined Callback Functions:

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A callback function is just nothing but called function, a function which has as an argument into another function.

To use a function as a callback function, pass a string containing the name of the function as the argument of another function:

Any existing function can be used as a callback function.

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<?php

function CarDetails($car) {

  return $car . "! ";

}

​

​

function printFormatted($car, $func) {

  // Calling the $func callback function

  echo $func($car);

}

​

// Pass "CarDetails" as callback functions to printFormatted()

printFormatted("Audi car", "CarDetails");

?>