A successful DosOpen request returns a handle for accessing the file. A file handle of zero is valid. The read/write pointer is set at the first byte of the file. The position of the pointer can be changed with DosSetFilePtr or by read and write operations on the file.

The file's date and time can be queried with DosQueryFileInfo. They are set with DosSetFileInfo.

The read-only attribute of a file can be set with the ATTRIB command.

ulAttribute cannot be set to Volume Label. To set volume-label information, issue DosSetFSInfo with a logical drive number. Volume labels cannot be opened.

cbFile affects the size of the file only when the file is new or a is replacement. If an existing file is opened, cbFile is ignored. To change the size of the existing file, issue DosSetFileSize.

The value in cbFile is a recommended size. If the full size cannot be allocated, the open request may still succeed. The file system makes a reasonable attempt to allocate the new size in an area that is as nearly contiguous as possible on the medium. When the file size is extended, the values of the new bytes are undefined.

The Direct Open bit provides direct access to an entire disk or diskette volume, independent of the file system. This mode of opening the volume that is currently on the drive returns a handle to the calling function; the handle represents the logical volume as a single file. The calling function specifies this handle with a DosDevIOCtl Category 8, DSK_LOCKDRIVE request to prevent other processes from accessing the logical volume. When you are finished using the logical volume, issue a DosDevIOCtl Category 8, DSK_UNLOCKDRIVE request to allow other processes to access the logical volume.

The file-handle state bits can be set by DosOpen and DosSetFHState. An application can query the file-handle state bits, as well as the rest of the Open Mode field, by issuing DosQueryFHState.

You can use an EAOP2 structure to set extended attributes in peaop2 when creating a file, replacing an existing file, or truncating an existing file. No extended attributes are set when an existing file is just opened.

A replacement operation is logically equivalent to atomically deleting and re-creating the file. This means that any extended attributes associated with the file also are deleted before the file is re-created.