|::LockFileEx doesn't work ?

See more:

C++

Win32

API

Does anyone have any idea why after locking a file I can still read and write it using a hex editor??? My code is below. LockFileEx doesn't fail. I have not written the Unlock code yet (so it is impossible to have been unlocked accidentally). The file seems to be still open when I read/write it. I try to lock the entire file.
I just wonder if someone can find any silly mistake I'm making (if any) and save me from a lot of search time. Thanks in advance.

LARGE_INTEGER LI;
memset(&LI, 0, sizeof(LI));
BOOL ret = ::GetFileSizeEx(hFile, &LI);
if(ret==0) goto ER;

OVERLAPPED ov;
memset(&ov, 0, sizeof(ov));
ov.hEvent = NULL;
ov.Offset = 0;
ov.OffsetHigh = 0;
ov.Pointer = NULL;
ov.Internal = 0;
ov.InternalHigh = 0;
ret = ::LockFileEx(hFile, LOCKFILE_EXCLUSIVE_LOCK|LOCKFILE_FAIL_IMMEDIATELY, 0, LI.LowPart, LI.HighPart, &ov);
if(ret==0) goto ER;