This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding Linux
manual page for details of Linux behavior), or the interface may not be
implemented on Linux.
ftell, ftello — return a file offset in a stream
long ftell(FILE *stream);
off_t ftello(FILE *stream);
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here
and the ISO C standard is unintentional. This volume of
POSIX.1‐2017 defers to the ISO C standard.
The ftell() function shall obtain the current value of the
file-position indicator for the stream pointed to by stream.
The ftell() function shall not change the setting of
errno if successful.
The ftello() function shall be equivalent to
ftell(), except that the return value is of type off_t and the
ftello() function may change the setting of errno if
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, 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
- 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,
FIFO, or socket.
The following sections are informative.
Section 2.5, Standard I/O Streams, fgetpos(),
fopen(), fseek(), lseek()
The Base Definitions volume of POSIX.1‐2017,
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1-2017, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018
Edition, Copyright (C) 2018 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 .
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