The concept and usage of PHP callback function

This article mainly introduces the concept and usage of PHP callback function, briefly introduces the concept and principle of the callback function, and analyzes the related use technique of the callback function with the example form, and the friends who need can refer to the following

Specific as follows:

First, the concept of callback function

First look at the callback function in C: The callback function is a function called through a function pointer. If you pass the pointer (address) of the function as an argument to another function, when the pointer is used to invoke the function it points to, we say this is a callback function. The callback function is not called directly by the implementing party of the function, but is invoked by another party when a particular event or condition occurs, and is used to respond to the event or condition.

The concept of callback functions in other languages is similar, except that the implementation mechanism of callbacks in various languages is different, and in layman's terms, the callback function is a function we define, but it is not called directly, but by another function. This function implements a call to a callback function by receiving its name and arguments.

Second, the implementation of the callback function in PHP

PHP provides two built-in functions call_user_func() and call_user_func_array() provides support for callback functions. The difference between the two functions is that Call_user_func_array receives the parameters of the callback function in the form of an array, and the prototype will know:mixed Call_user_func_array (callable $ Callback, Array$param_arr), it has only two parameters. and Call_user_func ($callback, parameter 1, parameter 2, ...) The number of parameters is determined based on the parameters of the callback function.

How to implement callbacks for global functions in scripts, non-static methods that do not use $this in classes, non-static methods that use $this in classes (need to pass in objects), static methods in classes, and the code passed by the test.

<?php//normal functions function F1 ($arg 1, $arg 2) {echo __function__. ' Exec,the args is: '. $arg 1. '  '. $arg 2; echo "<br/>";}  Call the function through Call_user_func f1call_user_func (' F1 ', ' Han ', ' Wen ');  The function Call_user_func_array (' F1 ', Array (' Han ', ' Wen ')) is called through Call_user_func_array, and class a{public $name; Function Show ($arg 1) {echo ' The arg is: '. $arg 1. "    <br/> ";    Echo ' My name is: '. $this->name;  echo "<br/>"; } function Show1 ($arg 1, $arg 2) {echo __method__. ' Exec,the args is: '. $arg 1. ' '. $arg 2. '  <br/> "; The public static function Show2 ($arg 1, $arg 2) {echo __method__. ' of class A exec, the args is: '. $arg 1. ' '. $arg 2. '  <br/> "; }}//calls a non-static member function in the class that has $this called the member in the object $ A = new A; $a->name = ' wen '; Call_user_func_array (Array ($a, ' show ',), Array (' han! ')); /Call class non-static member function, no object is created, this member function cannot have $thiscall_user_func_array (array (' A ', ' Show1 ',), Array (' han! ', ' Wen '));// Call the static member function in the Class Call_user_func_array (Array (' A ', ' show2 '), Array (' argument1 ', ' argument2 ')); 

Operation Result:

f1exec,the args Is:han wenf1exec,the args Is:han wenthe arg is:han!my name Is:wena::show1 exec,the args is:han! Wena::show2 of Class A exec, the args is:argument1 argument2

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