Linux and Windows use
0 to indicate that the operation is successful and an integer that is larger than 0 for some errors.
Linux System Error Codes
On Linux, the system error codes is defined in 2 headers which you can find on your own box:
You can view those for Linux 3.13.7 here:
Windows System Error Codes
For Windows, please find a list of error codes on MSDN: http://msdn.microsoft.com/en-us/library/windows/desktop/ms681381(v=vs.85).aspx