This simple function will check if a file exists, this could be good to use when you have to include a config file.

<? 

if (!file_exists("config.php")){ 

    die("Please check that the config file exists and is readable"); 

}else{ 

    include ("config.php"); 

} 

?>

This checks if the file exists, if the file doesnt exist then it will stop executing and display the error message. Although if it does exist then it will carry on and include the file.