本文介绍了PHP中函数前的感叹号是什么意思的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
Just as in the title, what does an exclamation mark before a function really mean in PHP?
For example is the following statement:
if (!stripos($haystack, $needle)) {}
the same as this:
if (stripos($haystack, $needle) === FALSE) {}
or this:
if (stripos($haystack, $needle) == FALSE) {}
Any clarification would be appreciated
解决方案
The ! preceding the function is the same as...
if (stripos($haystack, $needle) == FALSE) {}
It's the same because it is a == comparison which doesn't check types.
It's called the negation unary operator. It flips the Boolean value (coercing to Boolean if need be) of a value.
For example...
! 0; // True
! 1 ; // False
! ''; // True
! true; // False
!! 0 // False
The !! trick is handy in languages without a (bool) cast. By flipping a value twice, you get the Boolean version of its original value.
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