How to use PHP callback functions (detailed examples)

In the previous article, I brought you "How to play with PHP custom functions (summary sharing)". This article introduces the custom functions in PHP in detail. This article This article takes a look at the basic callback functions in PHP functions. I hope to be helpful!

PHP callback function

Callback function, a function structure that can cooperate with anonymous functions and variable functions to achieve more functions .

What is a callback function?

The callback function in PHP actually means that when calling a function, instead of passing standard variables to the function as parameters, another function is passed as a parameter to the called function. The callback function is the function that takes the parameter.

It can be understood that the callback function is also a function we defined, but it is not called directly, but requires another function to be called.

The example is as follows:

<?php
    function arithmetic($a, $b, $c) {
        return $a($b, $c);
    }
    function add($b,$c){
        return $b+$c;
    }
    $d = arithmetic(&#39;add&#39;, 5, 9);
    echo &#39;5 + 9 =&#39;.$d;
?>

Output result:

In addition, PHP provides two functionscall_user_func() and call_user_func_array() to support callback functions.

The difference between these two functions is: call_user_func_array() receives the parameters of the callback function in the form of an array, while call_user_func() receives the parameters of the callback function in the form of specific parameters.

• call_user_func_array()

The call_user_func_array function can call the callback function and then use an array as the parameter of the callback function . The syntax format is as follows:

call_user_func_array ($callback ,$param_arr)

In the syntax format, $callback is the called callback function, $param_arr is an index array, let’s take an example to see it in practice:

<?php
    function arithmetic($f, $m, $n) {
        return call_user_func_array($f, array($m, $n));
    }
    function add($m,$n){
        return $m+$n;
    }
    $sum = arithmetic(&#39;add&#39;, 3, 4);
    echo &#39;3 + 4 =&#39;.$sum;
?>

Output result:

• ##call_user_func()

call_user_func function will One parameter is called as a callback function. The syntax format is as follows:

call_user_func ($callback [, $parameter, ... ])

Among them, $callback is the called callback function, and the remaining parameters are the parameters of the callback function. Use "

," between multiple parameters. "separated. Let’s take an example to see it in action:

<?php
    function arithmetic($f, $m, $n) {
        return call_user_func($f, $m, $n);
    }
    function add($m,$n){
        return $m+$n;
    }
    $sum = arithmetic(&#39;add&#39;, 250, 250);
    echo &#39;250 + 250 =&#39;.$sum;
?>

Output result:

Next, I will share with you a combination of variable function and callback function. Example:

<?php
function woziji($one,$two,$func){
       //我规定：检查$func是否是函数，如果不是函数停止执行本段代码，返回false
       if(!is_callable($func)){
               return false;
       }
       //我把$one、$two相加，再把$one和$two传入$func这个函数中处理一次
       //$func是一个变量函数，参见变量函数这一章
       echo $one + $two + $func($one,$two);
}
//我们定义几个函数试试
function plusx2( $foo , $bar){
       $result = ($foo+$bar)*2;
       return $result;
}
function jian( $x , $y ){
   $result = $x - $y;
   return $result;
}
//调用一下函数，woziji，向里面传入参数试试
echo woziji(20,10,&#39;plusx2&#39;);
//将plusx2改成jian试试结果
echo woziji(20,10,&#39;jian&#39;);
?>

Output result:

Recommended learning: "

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