UnlockFile

The UnlockFile function unlocks a region in an open file. Unlocking a region enables other processes to access the region.

BOOL UnlockFile(
  HANDLE hFile,           // handle of file to unlock
  DWORD dwFileOffsetLow,  // low-order word of lock region offset
  DWORD dwFileOffsetHigh,  // high-order word of lock region offset
  DWORD nNumberOfBytesToUnlockLow,
                          // low-order word of length to unlock
  DWORD nNumberOfBytesToUnlockHigh 
                          // high-order word of length to unlock
);
 

Parameters

hFile

Handle to a file that contains a region locked with LockFile. The file handle must have been created with either GENERIC_READ or GENERIC_WRITE access to the file.

dwFileOffsetLow

Specifies the low-order word of the starting byte offset in the file where the locked region begins.

dwFileOffsetHigh

Specifies the high-order word of the starting byte offset in the file where the locked region begins.

nNumberOfBytesToUnlockLow

Specifies the low-order word of the length of the byte range to be unlocked.

nNumberOfBytesToUnlockHigh

Specifies the high-order word of the length of the byte range to be unlocked.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

Unlocking a region of a file releases a lock on the file. The region to unlock must correspond exactly to an existing locked region. For example, two adjacent regions of a file cannot be locked separately and then unlocked as a single region that spans both locked regions.

A process should not be terminated with a portion of a file locked and a file that has locked regions should not be closed.

This function works on a file allocation table (FAT) – based file system only if the operating system is running SHARE.EXE.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in winbase.h.
  Import Library: Use kernel32.lib.

See Also

File I/O Overview, File Functions, CreateFile, LockFile