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

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

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

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.