fseek, ftell, rewind - reposition a stream
fseek(stream, offset, ptrname)
Fseek sets the position of the next input or output operation on the
stream. The new position is at the signed distance offset bytes from
the beginning, the current position, or the end of the file, according
as ptrname has the value 0, 1, or 2.
Fseek undoes any effects of ungetc(3).
Ftell returns the current value of the offset relative to the beginning
of the file associated with the named stream. It is measured in bytes
on UNIX; on some other systems it is a magic cookie, and the only fool-
proof way to obtain an offset for fseek.
Rewind(stream) is equivalent to fseek(stream, 0L, 0).
Fseek returns -1 for improper seeks.