PHP strpos

Summary: in this tutorial, you’ll learn how to use the PHP strpos() function to get the index of the first occurrence of a substring in a string.

Introduction to the PHP strpos() function

The PHP strpos() function returns the index of the first occurrence of a substring within a string.

Here’s the syntax of the strpos() function:

strpos ( string $haystack , string $needle , int $offset = 0 ) : int|false
Code language: PHP (php)

The strpos() function has the following parameters:

  • The $haystack is a string to search in.
  • The $needle is a string value to search for.
  • The $offset is an integer that represents the index at which the strpos() function starts the search. The $offset defaults to 0.

The $offset can be positive or negative. If $offset is positive, the strpos() function starts the search at $offset number of characters to the end of the string.

If the $offset is negative, the strpos() function starts at the $offset number of characters to the beginning of the string.

If the strpos() doesn’t find the $needle in the $haystack, it returns false.

PHP strpos() function examples

Let’s take some examples of using the strpos() function.

1) Using PHP strpos() function to search for a substring example

The following example uses the strpos() function to search for the substring 'to' in the string 'To do or not to do':

<?php $str = 'To do or not to do'; $position = strpos($str, 'do'); echo $position; // 3
Code language: PHP (php)

Output:

3
Code language: PHP (php)
php strpos

2) Using PHP strpos() function to search for a substring with an offset example

The following example uses the strpos() function to search for the substring 'do' in the string 'To do or not to do' start from the index 5:

<?php $str = 'To do or not to do'; $position = strpos($str, 'do', 4); echo $position;
Code language: PHP (php)

Output:

16
Code language: PHP (php)

In this example, the strpos() returns the index of the second occurrence of the 'do' substring because it starts the search at index 4.

PHP strpos() function with offset

3) Using PHP strpos() function gotchas

The following example uses the strpos() function to search for the substring 'To' in the string 'To do or not to do':

<?php $str = 'To do or not to do'; $position = strpos($str, 'To'); if ($position) { echo $position; } else { echo 'Not found'; }
Code language: PHP (php)

Output:

Not found
Code language: PHP (php)

The string 'To' locates at the beginning of the string; therefore, the strpos() function returns 0. However, PHP evaluates 0 as false. So you see the 'not found' message in the output.

To avoid this issue, you should always compare the result of the strpos() function with true or false using the === or !== operator. For example:

<?php $str = 'To do or not to do'; $position = strpos($str, 'To'); if ($position !== false) { echo $position; // 0 } else { echo 'Not found'; }
Code language: PHP (php)

Output:

0
Code language: PHP (php)

PHP stripos() function

The stripos() function is like the strpos() function except that it searches for the substring case-insentively. The following example returns false:

<?php $str = 'PHP is cool'; $position = strpos($str, 'php'); var_dump($position); // bool(false)
Code language: PHP (php)

Output:

0
Code language: PHP (php)

To search for a substring case-insensitively, you use the stripos() function:

<?php $str = 'PHP is cool'; $position = stripos($str, 'php'); var_dump($position); // 0
Code language: PHP (php)

Summary

  • Use the strpos() function to return the index of the first occurrence of a substring in a string.
  • Use the stripos() function to search for the substring case-insensitively.
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