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PHP运算符问题

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WBOYOriginal
2016-06-06 20:33:431339browse

为什么if ($a = 100 && $b = 200) {var_dump($a, $b);}输出bool(true) int(200)
PHP运算符问题

<code><?php if ($a = 100 && $b = 200) {
    var_dump($a, $b);
}
</code></code>

回复内容:

为什么if ($a = 100 && $b = 200) {var_dump($a, $b);}输出bool(true) int(200)
PHP运算符问题

<code><?php if ($a = 100 && $b = 200) {
    var_dump($a, $b);
}
</code></code>

&&优先级比=高,所以会$a = (100 && $b = 200),在http://php.net/manual/en/language.operators.precedence.php中有一句
Although = has a lower precedence than most other operators, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the return value of foo() is put into $a.,虽然&&优先级高于=,但是200还是会被赋值给$b,由于100 && $b = 200均为真返回true,所以$a=true

实际上的优先级是这样的:

<code><?php if ($a = (100 && $b = 200)) {
    var_dump($a, $b);
}
</code></code>

所以$a是true。

赋值不是比较,你可能看错了

老生常谈的问题了

实际上是这样运行的

<code>php</code><code><br>if($a = (100 && $b = 200)){
    var_dump($a, $b);
}
</code>
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