mkdir is a C runtime library function that creates directories.

In contrary to what could be understood from the MSDN documentation:

“…On an error, the function returns –1 and sets errno as follows.EEXIST Directory was not created because dirname is the name of an existing file, directory, or device.ENOENT Path was not found.For more information about these and other return codes, see _doserrno, errno, _sys_errlist, and _sys_nerr.”

mkdir might return other error values. For example when calling mkdir on an existing directory the function might return EEXIST but can also return EACCES (permission denied). The function error results seem to differ according to user access permissions on the system. This has been tested on Windows 2003/Vista/7. For more information and portability issues check out this discussion about mkdir portability in Kernel trap.

·         Note that this discussion applies to Microsoft’s implementation of the C run time library.