var_dump(DIRECTORY_SEPARATOR) // string '\' (length=1)
var_dump(file_exists("C:/1212.txt")); // true
var_dump(file_exists("C:\1212.txt")); // false
var_dump(file_exists("C:".DIRECTORY_SEPARATOR."1212.txt")); // false

DIRECTORY_SEPARATOR ne yapar? Neden kullanırken yukarıdaki durumda false DIRECTORY_SEPARATOR?