PHP运算符差异&&和“和”[重复](PHP operator difference && and “and” [duplicate])

PHP运算符差异&&和“和”[重复](PHP operator difference && and “and” [duplicate])

可能重复： 'AND'和'&&'作为运算符

对不起，基本的问题，但我开始学习PHP只是一个星期前，并找不到在谷歌/ stackoverflow这个问题的答案。

我经历了下面的程序：

$one = true; $two = null; $a = isset($one) && isset($two); $b = isset($one) and isset($two); echo $a.'<br>'; echo $b;

它的输出是：

false true

我读&& /和是一样的。 两者的结果有何不同？ 有人能说出真实的原因吗？

Possible Duplicate: 'AND' vs '&&' as operator

Sorry for very basic question but I started learning PHP just a week ago & couldn't find an answer to this question on google/stackoverflow.

I went through below program:

$one = true; $two = null; $a = isset($one) && isset($two); $b = isset($one) and isset($two); echo $a.'<br>'; echo $b;

Its output is:

false true

I read &&/and are same. How is the result different for both of them? Can someone tell the real reason please?

最满意答案

原因是运营商优先 。 在您使用&& and ＆ =三个运算符中，优先顺序是

&& = and

因此，程序中的$b按照预期进行计算，但对于$b ，首先计算语句$b = isset($one) ，从而给出意想不到的结果。 它可以如下修复。

$b = (isset($one) and isset($two));

The reason is operator precedence. Among three operators you used &&, and & =, precedence order is

&& = and

So $a in your program calculated as expected but for $b, statement $b = isset($one) was calculated first, giving unexpected result. It can be fixed as follow.

$b = (isset($one) and isset($two));