The ftello function is identical to the ftell function, except
    that the return value is of type off_t instead of long int.

    The off_t data type is either a 64-bit or 32-bit integer. The 64-
    bit interface allows for file sizes greater than 2 GB, and can be
    selected at compile time by defining the _LARGEFILE feature-test
    macro as follows:

    CC/DEFINE=_LARGEFILE