How to replace a nth occurrence in a string

Question

I need a simple and fast solution to replace nth occurrence (placeholder) in a string.

For example, nth question mark in sql query should be replaced with a provide

Answer 1

Instead of using question marks, why don't use markers like that :

$subject = "SELECT uid FROM users WHERE uid = :uid or username = :username";
$parameters = array(
    ':uid' => 42,
    ':username' => 'John',
);
$subject = str_replace(array_keys($parameters), $parameters, $subject);