Definition and Usage

PHP Version
5+

The stripos() function for strings searches for the specified substring in a string and returns the index of its first occurrence.
This function performs a case-insensitive search.
If the specified substring is not found, it returns false.

This function is useful for finding the position of a substring in a string or for checking whether it exists, in a case-insensitive manner.

Features

  • The comparison is case-insensitive.
  • This function does not support multi-byte strings such as Japanese, Korean, or Chinese.

Basic Example

PHP 
$str = 'Hello, World!';
$substring = 'world'; // Case-insensitive search

$pos = stripos($str, $substring);

if ($pos !== false) {
    echo "Found at position: $pos";
} else {
    echo 'Not found.';
}

// Output: Found at position: 7

/*
 * Note:
 * String indexes in PHP start at 0.
 * The index of the first character is 0, and the second character is 1.
 */

Useful Tips

  • For multi-byte strings such as Japanese, Korean, or Chinese, use the mb_stripos() function instead.
  • If you need a case-sensitive search, use the strpos() function.

Syntax

PHP 
stripos(string $haystack, string $needle, int $offset = 0): int|false

Parameters

Description of the parameters used in the stripos() function
$haystack The input string to be searched.
$needle The substring to search for.
The comparison is case-insensitive.
$offset Optional. The zero-based index at which to start the search.
  • If omitted, the default value is 0.
  • As of PHP 7.1.0, negative values are allowed. When a negative value is given, the search starts that many characters from the end of the string.

Return Values

Returns the position (index) of the first occurrence of the specified substring ($needle) within the input string ($haystack).

Note:
String positions (indexes) start at 0, not 1.

  • Returns false if the specified substring ($needle) is not found.
  • Returns false if the given substring ($needle) is an empty string ('').

Important:
The strpos() function triggers a warning in PHP versions earlier than 8.0 when the given substring ($needle) is an empty string (''), unlike stripos().

PHP versions earlier than 8.0 
$haystack = 'Hello, World!';

var_dump(stripos($haystack, '')); // bool(false)
var_dump(strpos($haystack, '')); // Warning: strpos(): Empty needle in

Changelog

Version history of the stripos() function
VersionDescription
8.2.0 Prior to PHP 8.2.0, the results of case-insensitive comparisons for certain non-ASCII characters (e.g., Japanese, Korean, Chinese) could vary depending on the setlocale() setting. Starting with PHP 8.2.0, only ASCII characters are compared in a case-insensitive manner; all other characters are compared at the byte level.
8.0.0 Empty strings ('') are now allowed for the $needle parameter.
8.0.0 Passing an integer (int) to the $needle parameter is no longer supported.
7.3.0 Passing an integer (int) to the $needle parameter has been deprecated.
7.1.0 Negative values are now allowed for the $offset parameter.

Things to Keep in Mind

String indexes start at 0.
The first character has an index of 0, and the second character has an index of 1.

PHP String indexes start at 0. 
$newstring = 'abcdef ghijk';
$pos = stripos($newstring, 'a');

var_dump($pos); // int(0)

Be careful when using this function's return value in a Boolean context.
To properly test the return value, always use the === operator.

If the specified substring ($needle) is found at the very beginning of the string ($haystack), the function returns 0.

However, because 0 is loosely evaluated as false in PHP, using == may lead to incorrect results. For strict comparison, use ===.

PHP Always use the === operator when testing the return value. 
$str = 'Hello, World!';
$substring = 'Hello';

$pos = stripos($str, $substring);

var_dump($pos); // int(0)

if ($pos === false) {
    echo "The string 'Hello' was not found.";
} else {
    echo "The string 'Hello' is included in the text.";
}

// Output: The string 'Hello' is included in the text.

Practical Examples

The stripos() function is useful for finding the position of a substring in a string. Its main feature is that it performs a case-insensitive search, allowing you to locate substrings without worrying about letter case.

Searching User Input

PHP 
$user_input = $_GET['search_query'];
$content = 'This is a sample text for searching.';

if (stripos($content, $user_input) !== false) {
    echo 'The search term was found.';
} else {
    echo 'The search term was not found.';
}

Case-Insensitive Substring Check

PHP 
$string = 'The school bell rings, time to gather!';
$search_term = 'Bell';

if (stripos($string, $search_term) !== false) {
    echo 'The search term was found.';
} else {
    echo 'The search term was not found.';
}

// Output: The search term was found.

Checking if a String Starts with a Specific Word

PHP 
$string = 'Hello, world!';
$prefix = 'hello';

if (stripos($string, $prefix) === 0) {
    echo "The string starts with '$prefix'.";
} else {
    echo "The string does not start with '$prefix'.";
}

// Output: The string starts with 'hello'.

References

See also