Why does a string in PHP not contain an empty string?

Question

Consider the following piece of code which somehow returns false:

<?php var_dump(stripos("foo", "")); ?>

It returns bool(false), not int(0) on PHP 7.4.

I thought every string contained the empty string.

So what is the cause of this behavior?

"Note that the needle may be a string of one or more characters.". — Alex Howansky, Jan 06 '22 at 01:51
This function returns the zero-based string offset where the needle can be found in the haystack. If empty strings were always a match, what offset should be returned? There's no way to extract an empty string from a PHP string using a offset. — Álvaro González, Jan 06 '22 at 13:09
In this example, `0` would also be `f`. An option could have been `-1`, but `$somestring[-1]` is not valid. — Álvaro González, Jan 07 '22 at 07:20

Yevgeniy Kosmak · Accepted Answer · 2022-01-06T01:59:52.780

1

Returns false if the needle was not found.

The purpose of this is possibility to strictly compare result with false in order to find out that needle is not found in haystack.

if (stripos("foo", "") === false) {
    // Here we definitely know "" is not contained in "foo"
}

edited Jan 06 '22 at 01:59

answered Jan 06 '22 at 01:51

Yevgeniy Kosmak

1

I thought `stripos("foo", "")` meant if `""` was contained in `"foo"`, not the other way around. – no ai please Jan 06 '22 at 01:58
Confused them, fixed, thanks. – Yevgeniy Kosmak Jan 06 '22 at 02:01

1 Answers1