PHP stripos() Function: Case‑Insensitive Search for a Substring Position

The stripos() function in PHP finds the position of the first occurrence of a needle string inside a haystack string without regard to case.

Syntax:

int stripos(string $haystack, string $needle [, int $offset = 0])

Description: It returns the numeric position where $needle first appears in $haystack. The search can start at an optional $offset, but the returned position is always relative to the beginning of $haystack.

Parameters:

haystack : The string to be searched.

needle : The string (or single character) to look for; non‑string values are cast to integers.

offset (optional): The character position in $haystack where the search should begin.

Return value: The function returns the position of $needle in $haystack (starting at 0). If the needle is not found, it returns FALSE.

Example:

<?php
$findme = 'a';
$mystring1 = 'xyz';
$mystring2 = 'ABC';

$pos1 = stripos($mystring1, $findme);
$pos2 = stripos($mystring2, $findme);

// $pos1 will be FALSE because 'a' is not in 'xyz'
if ($pos1 === false) {
    echo "The string '$findme' was not found in the string '$mystring1'";
}

// $pos2 will be 0 because 'a' (case‑insensitive) is at the start of 'ABC'
if ($pos2 !== false) {
    echo "We found '$findme' in '$mystring2' at position $pos2";
}
?>

The example demonstrates that a strict identity check ( ===) is required to distinguish a valid position of 0 from FALSE, and shows how stripos() behaves with different case variations.