require() fails even though file_exists() claims file is there

Question

Here is my code:

if (file_exists('config.php')) {
    require('config.php'); // This is line 38
}

Which somehow produces the error:

Warning: require(config.php) [function.require]: failed to open stream: No such file or directory in /path/name/file.php on line 38

How on earth is this possible?

Update: The following does work:

if (file_exists(getcwd(). '/config.php')) {
     require(getcwd(). '/config.php');
}

Answer 1

Try absolute path. Using dirname(__FILE__).

require(dirname(__FILE__) . '/config.php');

Answer 2

The PHP include and require operate in the same way and use an include path (include). Therefore will use this path to find the file and if you have not set it correctly it will not look in the current directory.

Use get include path to find out the value for this.