A brief discussion on the usage of goto syntax in PHP

This article will introduce to you how to use goto syntax in PHP. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

Usage of goto syntax in PHP

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In C, Java and many languages, there is a magic The syntax is goto. As the name suggests, its use is to go somewhere directly. From a code perspective, it means jumping directly to the specified place. We also have this function in PHP. Let's first take a look at how it is used:

goto a;
echo "1"; // 不会输出

a:
echo '2'; // 2

When the code runs to the goto position, it jumps to the line of code where a: is located and continues execution. . It feels very fun. This function is very useful for complex nested ifs or jumping out of some loops, especially for handling certain exceptions or error situations, such as:

for ($i = 0, $j = 50; $i < 100; $i++) {
    while ($j--) {
        if ($j == 17) { // 假设$j==17是一种异常情况
            goto end; // 直接跳走了，循环结束的结果也不输出了
        }

    }
}
echo "i = $i";
end:
echo &#39;j hit 17&#39;; // 直接到这里输出或者处理异常情况了

It feels pretty good, right? However, the goto syntax also has some limitations:

• The target location can only be located in the same file and scope, which means that you cannot jump out of one function or class method, nor into another. The function
• cannot jump into any loop or switch structure
• To jump out of the loop or switch, the usual usage is to use goto instead of multiple layers break

For example, the following codes are invalid:

$a = 1;
goto switchgo;
switch ($a){
    case 1:
        echo 'bb';
    break;
    case 2:
        echo 'cc';
        switchgo:
            echo "bb";
    break;
}

goto whilego;
while($a < 10){
    $a++;
    whilego:
        echo $a;
}


// Fatal error: &#39;goto&#39; to undefined label &#39;ifgo&#39;

They will all report the same error because the defined goto tag cannot be found due to the scope. In addition, it should be noted that using goto may cause an infinite loop, as shown below:

b:
    echo 'b';

goto b;

When the code is executed to goto, it jumps back to the previous b label line, and then continues to execute downwards, reaching goto again. , became an endless loop. It feels a bit like while(true). However, there is no break in this goto loop, you can only go to other places in goto.

So, the use of goto syntax is very rare, because it will disrupt the logical flow of your code, but people who like it will feel that it can make the code very flexible. This requires a judgment of benevolence and wisdom. Currently, the use of this syntax is not strongly advocated in the documentation of most languages, including PHP. My suggestion is that if it is not a very special situation or to show off your skills, try not to use goto syntax. When the project code becomes complicated, it is easy to confuse others or yourself.

测试代码：https://github.com/zhangyue0503/dev-blog/blob/master/php/201911/goto%E8%AF%AD%E6%B3%95%E5%9C%A8PHP%E4%B8%AD%E7%9A%84%E4%BD%BF%E7%94%A8.md

参考文档：https://www.php.net/manual/zh/control-structures.goto.php

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