Updated: October 2010
Changes the working drive.
If drive is not in the range from 1 through 26, the invalid-parameter handler is invoked as described in Parameter Validation. If execution is allowed to continue, the _chdrive function returns -1, errno is set to EACCES, and _doserrno is set to ERROR_INVALID_DRIVE.
The _chdrive function is not thread-safe because it depends on the SetCurrentDirectory function, which is itself not thread-safe. To use _chdrive safely in a multi-threaded application, you must provide your own thread synchronization. For more information, see SetCurrentDirectory at MSDN Library.
The _chdrive function changes only the working drive; _chdir changes the working directory.