PHP strpos Examples

Here is a short summary on what not to do wrong when using strpos() and what other matching methods do exist in PHP.

Important: Use Correct Operator!

Most PHP beginners fall for this:
WRONG
if (strpos($str, $substr) != false) {
if (strpos($str, $substr) == false) {
CORRECT
if (strpos($str, $substr) === false) {
if (strpos($str, $substr) !== false) {
The reason for using the identical operators (that also check for the type of the value) "===" or "!==" is that strpos() might return "0" for match at the beginning or "false" for no match which cannot be distinguished by "==" or "!=". Simple rule: With strpos() functions always compare to "false" with the identical operators.

Case Sensitivity

It is simple:
strpos()case sensitive searching
stripos()case insensitive searching

Search From Offset

If you want to continue a search or want to skip something at the start use an offset as third parameter:
if (strpos($str, $substr, 5) === false) {
By using the return value of strpos() you can do repeated searches:
$pos1 = strpos($str, $substr);
$pos2 = strpos($str, $substr, $pos1 + strlen($pos1));

Search Backwards

There is an additional set of methods for backwards searching:
strrpos()case sensitive backwards searching
strripos()case insensitive backwards searching

Extract Found Strings

If you want to extract a string at the position you've found you need to use the substr() method. An example:
$pos = strpos($str, $substr);
$result = substr($str, $pos);

When not to use strpos()?

Do not use strpos() if you want to do the following things:
  1. Test for a pattern at the start or end of a string -> use preg_match()
  2. Extract multiple substrings -> use preg_match()
  3. Match a string for a complex pattern -> use preg_match()
  4. If you want to split a string a delimiters -> use strpbrk()

About Performance

If you are wondering how fast strpos() is compared to using regular expressions check this post: strpos() vs preg_match()