PHP function callback function (2) call_user_func_array() function

Callback function Pass a function as a parameter to the called function. If a parameter of type callback appears in the format description of a function, the function is a callback function. Although you can use variable functions to declare your own callback functions, the most common implementation is through the call_user_func_array() function. The previous chapter introduced the declaration and application of variable functions in php callback functions. Using variable functions to pass a user-defined execution process to the function for use greatly increases the user's expansion of function functions. Pass a self-defined function to the function for use. This section explains the call_user_func_array() function with an example.

The function call_user_func_array() is a built-in function in PHP. In fact, it is also a callback function. Its format is as follows:

mixed call_user_func_array( callback function, array param_arr)

This function has two parameters: the first parameter uses a pseudo-type callback, so this parameter requires a string, indicating the name of the function to be called; the second parameter is an array type parameter, indicating the parameter list, according to The message is passed once to the function to be called. Declare a function whose function is output and whose purpose is to serve as the callback function of the function.

The application example of this function is as follows:

<?php
 // 声明一个函数fun(),功能是输出两个字符串，目的是作为call_user_func_array()函数的回调函数
 function fun($str1, $str2){
   echo "$str1 = ".$str1;
   echo "<br>";
   echo "$str2 = ".$str2;
 }
 //通过系统函数call_user_func_array()调用函数fun()
 call_user_func_array("fun",array("php.cn","php中文网"));
?>

In the above example, through the system function call_user_func_array () Call the self-defined function fun() and pass the name string of the function fun() 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. The number must be the same as the parameter list and tree of the fun() function. Because each element value in this array parameter will be passed to the callback function fun() parameter list in order through the call_user_func_array() function. So we can change the custom callback function implemented through the variable function to the call_user_func_array() function.

An example of the code is as follows:

<?php
 //声明回调函数filter, 在0-10的整数中通过自定义条件过滤不要的数字
 function filter($fun){
   for($i=0; $i<=10; $i++){
     //使用系统函数call_user_func_array()，调用和变量$fun值相同的函数
     if(call_user_func_array($fun,array($i)))
       continue;
     echo $i.&#39;<br>&#39;;
   }
 }
?>

In this example, inside the custom function filter(), the original variable function position is rewritten to The call_user_func_array() function is called, but the application method of the function filter() has not changed.

This chapter explains the call_user_func_array() function of the PHP callback function and its usage. In the next chapter, we will introduce the class static function and object method callback of the PHP callback function.

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