How to find index of a substring in a string in PHP?

In this PHP tutorial, you shall learn how to find the index of a specific substring in a given string using strpos() function, with example programs.

PHP – Find index of a substring in a string

To find the index of a substring in a string in PHP, call strpos() function and pass given string and substring as arguments.

The strpos() function returns an integer value of the index if the substring is present in the string, else, the function returns a boolean value of false.

Syntax

The syntax to find the index of substring search in the string str is

strpos($str, $search)

Examples

1. Positive Scenario – String contains search string

In this example, we take string values in str and search. We find the index of first occurrence of the search string search in the string str.

For given input values, strpos() returns an integer value of 9.

PHP Program

<?php
  $str = 'Apple is red in color.';
  $search = 'red';
  $index = strpos($str, $search);
  echo "Index of substring : " . $index;
?>

Output

2. Negative Scenario – String does not contain search string

In this example, we take a string in str and search string search, such that the string str does not contain search.

For given input values, strpos() returns false.

PHP Program

<?php
  $str = 'Apple is red in color.';
  $search = 'yellow';
  $index = strpos($str, $search);
  echo "Index of substring : " . $index;
?>

Output

Conclusion

In this PHP Tutorial, we learned how to find the index of a substring (search string) in a given string, using strpos() function, with the help of examples.