folgendes steht im
msdn zu SetFilePointer (was intern durch seek aufgerufen wird)
Zitat:
You can use SetFilePointer to determine the length of a file. To do this, use FILE_END for dwMoveMethod and seek to location zero (0). The file offset returned is the length of the file. However, this practice can have unintended side effects, for example, failure to save the current file pointer so that the program can return to that location. It is best to use GetFileSize instead.