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UnlockFile Function

The UnlockFile function releases a previously locked region of a file.

Syntax

            
                BOOL UnlockFile(

                  HANDLE hFile,

                  DWORD dwFileOffsetLow,

                  DWORD dwFileOffsetHigh,

                  DWORD nNumberOfBytesToUnlockLow,

                  DWORD nNumberOfBytesToUnlockHigh

                );

Parameters

Parameter	Description
`hFile`	A handle to the file that contains the locked region. This handle must have been created by a call to the `CreateFile` function.
`dwFileOffsetLow`	The low-order 32 bits of the starting byte offset of the region to unlock.
`dwFileOffsetHigh`	The high-order 32 bits of the starting byte offset of the region to unlock.
`nNumberOfBytesToUnlockLow`	The low-order 32 bits of the number of bytes to unlock.
`nNumberOfBytesToUnlockHigh`	The high-order 32 bits of the number of bytes to unlock.

Return Value

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

The UnlockFile function releases byte-range locks previously placed on a file by the LockFile function. The parameters specify the file handle, the starting offset of the locked region, and the number of bytes in the locked region.

It is important that the parameters passed to UnlockFile exactly match those used in the corresponding LockFile call. If there is a mismatch, the behavior is undefined.

This function is typically used in scenarios where multiple processes might need to access different parts of the same file concurrently. By using LockFile and UnlockFile, applications can ensure data integrity by preventing simultaneous modification of critical file sections.

Important Considerations:

All locks on a file are released automatically when the file handle is closed.
This function does not grant or release access to the file. It only affects byte-range locks.
Ensure that the file handle has the necessary access rights for file operations.

Requirements

Attribute	Value
Minimum supported client	Windows 2000 Professional
Minimum supported server	Windows 2000 Server
Header	`fileapi.h`
Library	`Kernel32.lib`
DLL	`Kernel32.dll`