The ftell() function shall obtain the current value of the file-position
indicator for the stream pointed to by
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 the error.
The ftell() and ftello() functions
shall fail if:
The file descriptor underlying stream is not an open file descriptor.
For ftell(), the current file offset cannot be represented correctly
in an object of type long.
For ftello(), the current file offset cannot be represented
correctly in an object of type off_t.
The file descriptor underlying stream is associated with a pipe
The ftell() function may fail if:
The file descriptor underlying stream is associated with a socket.
The following sections are informative.
fgetpos() , fopen() , fseek()
, lseek() , the Base Definitions volume of IEEE Std 1003.1-2001,
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