CFile seek backward

[C++ Programming]

Hi

I want to use CFile to seek backward. I did following:

int CmyClass::seekPos(CArchive& ar)
{
...
CFile* fp = ar.GetFile();
ULONGLONG lActual = fp->Seek( -5, CFile::current ); ----------> get error.
...
}


I found lActual = 12283? What is wrong?

Thanks,