Understanding PHP strpos(): Finding the Position of a Substring

The article introduces the PHP strpos() function, which searches for the first occurrence of a substring within a string and returns its numeric position.

Syntax :

mixed strpos(string $haystack, mixed $needle, int $offset = 0)

Parameters

haystack : The string to be searched.

needle : The substring to look for; if not a string it is converted to an integer representing a character code.

offset : Optional start position for the search; must be a non‑negative integer.

Return value : The position of needle in haystack (starting from 0) or FALSE if the needle is not found.

Example 1 – Basic usage

<?php
$mystring = 'abc';
$findme   = 'a';
$pos = strpos($mystring, $findme);
if ($pos === false) {
    echo "The string '$findme' was not found in the string '$mystring'";
} else {
    echo "The string '$findme' was found in the string '$mystring'";
}
echo " and exists at position $pos";
?>

This example shows a straightforward search and demonstrates the importance of using the strict comparison operator === because the position 0 is considered falsy in loose comparisons.

Example 2 – Using strict inequality

<?php
$mystring = 'abc';
$findme   = 'a';
$pos = strpos($mystring, $findme);
if ($pos !== false) {
    echo "The string '$findme' was found in the string '$mystring'";
    echo " and exists at position $pos";
} else {
    echo "The string '$findme' was not found in the string '$mystring'";
}
?>

Here the strict inequality !== is used to correctly handle the case where the needle is found at position 0.

Example 3 – Searching with an offset

<?php
$newstring = 'abcdef abcdef';
$pos = strpos($newstring, 'a', 1); // start searching after the first character
// $pos will be 7, not 0
?>

This demonstrates how the optional $offset parameter can be used to ignore characters before a certain index, allowing searches to begin later in the string.

Overall, the article provides a concise reference for using strpos() effectively in PHP backend development.