The callback function of PHP function (ii) Call_user_func_array () function

callback functionPasses a function as an argument to the called function. If a parameter of type callback is present in the format description of the function, the function is the callback function. Although variable functions can be used to declare their own callback functions, most of them are implemented by the Call_user_func_array () function. The previous chapter introduces the variable function declaration and application in the PHP callback function, using variable function to pass a user-defined execution procedure to the function, which greatly increases the user's extension to function function, and passes the function of one's own definition to the function internal use. This section describes the next Call_user_func_array () function as an example.

The function Call_user_func_array () is a built-in function in PHP, but it is also a callback function with the following format:

Mixed Call_user_func_array (callback function, array Param_arr)

The function has two parameters: the first parameter requires a string to represent the function name to invoke because it uses a pseudo-type callback, and the second parameter is an array-type parameter that represents the parameter list, which is passed to the function to be called once in a straight pass. Declares a function, which is output, and is intended to function as a callback function.

The application example for this function is as follows:

<?php//Declare a function fun (), function is to output two strings, the purpose is as the Call_user_func_array () function of the callback function fun ($str 1, $str 2) {   echo "$str 1 =". $str 1;   echo "<br>";   echo "$str 2 =". $str 2;} Call function Fun () by system function Call_user_func_array () Call_user_func_array ("Fun", Array ("php.cn", "PHP Chinese web")); >

In the above example, the function fun () is called by the system function Call_user_func_array (), and the name string of the function fun () is passed to the first parameter in the Call_user_func_array () function. The second parameter requires an array, and the number of elements in the array must be the same as the parameter list and tree of the fun () function. Because each element value in this array parameter is passed to the callback to the function fun () parameter list, in order, through the Call_user_func_array () function. So we can change the custom callback function, which is implemented by the variable function, into the way of the Call_user_func_array () function.

An example of its code is shown below:

<?php//Declaration callback function filter, in the integer 0-10 by the custom condition filtering does not have the number function filter ($fun) {for   ($i =0; $i <=10; $i + +) {     // Use the system function Call_user_func_array (), call the same function as the variable $fun value     if (Call_user_func_array ($fun, Array ($i)))       continue;     echo $i. ' <br> ';   } }?>

In this example, the Custom function filter () internally overwrites the original variable function position with the use of the Call_user_func_array () function, and the application of the function filter () has not changed.

This chapter explains the Call_user_func_array () function of the PHP callback function and its usage, and the next chapter introduces the class static function of the PHP callback function and the method callback of the object.

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