PHP的5 strpos()返回0和false之间的区别? [英] php 5 strpos() difference between returning 0 and false?

问题描述

if(strpos("http://www.example.com","http://www.")==0){ // do work}

我希望这能解决，但确实如此.但是当我这样做时会发生什么

I'd expect this to resolve as true, which it does. But what happens when I do

if(strpos("abcdefghijklmnop","http://www.")==0){// do work}

这在php 5上也可以通过，因为据我所知strpos返回false，它表示为0.

This also passes on php 5 because as far as I can work out the strpos returns false which translates as 0.

这是正确的想法/行为吗?如果是这样，测试该子字符串在另一个字符串的开头的解决方法是什么?

Is this correct thinking/behaviour? If so what is the workaround for testing for that a substring is at the beginning of another string?

推荐答案

是的，这是正确的/预期的行为:

Yes, this is correct / expected behavior :

当字符串开头存在匹配项时，
• strpos可以返回0
• ，如果没有匹配项，它将返回false

• strpos can return 0 when there is a match at the beginning of the string
• and it will return false when there is no match

问题是您不应该使用==来比较0和false；您应该像这样使用===:

The thing is you should not use == to compare 0 and false ; you should use ===, like this :

if(strpos("abcdefghijklmnop","http://www.") === 0) {

}

或:

if(strpos("abcdefghijklmnop","http://www.") === false) {

}

有关更多信息，请参见比较运算符:

For more informations, see Comparison Operators :

如果$a等于$b，则
• $a == $b将为TRUE.
如果$a等于$b，并且它们具有相同的类型，则
• $a === $b将是TRUE.

• $a == $b will be TRUE if $a is equal to $b.
• $a === $b will be TRUE if $a is equal to $b, and they are of the same type.

然后引用 strpos 的手册页:

And, quoting the manual page of strpos :

此函数可能返回布尔值 FALSE，但也可能返回一个 非布尔值，其计算结果为 FALSE，例如0或"".
请 请阅读布尔值部分 更多信息.
使用 === 运算符以测试退货 该函数的值.

This function may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE, such as 0 or "".
Please read the section on Booleans for more information.
Use the === operator for testing the return value of this function.

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