The LockFile function locks a region in an open file. Locking a region prevents other processes from accessing the region.
BOOL LockFile(
HANDLE hFile, // handle of file to lock
 
WORD dwFileOffsetLow, // low-order word of lock region offset
 
WORD dwFileOffsetHigh, // high-order word of lock region offset
 
WORD nNumberOfBytesToLockLow, // low-order word of length to lock
 
WORD nNumberOfBytesToLockHigh // high-order word of length to lock
 
;
Parameters
hFile
Identifies the file with a region to be locked. The file handle must have been created with GENERIC_READ or GENERIC_WRITE access to the file (or both).
dwFileOffsetLow
Specifies the low-order word of the starting byte offset in the file where the lock should begin.
dwFileOffsetHigh
Specifies the high-order word of the starting byte offset in the file where the lock should begin.
nNumberOfBytesToLockLow
Specifies the low-order word of the length of the byte range to be locked.
nNumberOfBytesToLockHigh
Specifies the high-order word of the length of the byte range to be locked.
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.