Why use !== FALSE to check stripos in php?

The answer is that in PHP a "false" value can be satisfied by a handful of values, such as an empty array, an empty string, a NULL, integer 0, etc. See the empty() function page for a full list:

http://php.net/empty

So this would always yield incorrect results:

if(strpos("abc", "a")) {   echo "Yes";} else {  echo "No";}

Since the "a" occurs at the first position (index 0) then PHP considers "if (0)" to be false.

When strpos does NOT find the needle in your haystack it will return the boolean FALSE, which is what you want to check with the triple-equal operator which checks both type and value. See the docs on comparison operators

http://www.php.net/manual/en/language.operators.comparison.php

stripos returns the position of a string inside another, and if the string is not found, it returns false, so it's recommended to use the identity comparison operators (===, !==), because PHP considers 0 as a "falsy" value, consider this example:

// Find the position of the 'a' character in the 'abc' string:stripos('abc', 'a') !== false; // true, position is 0stripos('abc', 'a') != false; // false, 0 is "falsy"

In PHP, !== means not of the same type AND value.

If stripos() returns anything other than false (and exactly 'false', and not zero), it means it has found something, even if the position is 0 and int(0) is returned. 0 and false are equal when doing a standard comparison with the == but not when using the identity === operator, so the only way to know if stripos() has found something for certain is to compare false's value and type using !== (not identical, ie of both the same type and value of strpos()'s return value.)