The ftell() function shall obtain the current value of the file-position
indicator for the stream pointed to by stream.
The ftello() function shall be equivalent to ftell(), except that
the return value is of type off_t.
Upon successful completion, ftell() and ftello()
shall return the current value of the file-position indicator for the
stream measured in bytes from the beginning of the file.
Otherwise, ftell() and ftello() shall return -1, cast to
long and off_t respectively, and set errno to indicate
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html