ftell man page
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
#include <stdio.h> 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.1-2008 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 successful.
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 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, 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.1-2008, <stdio.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
fgetpos(3p), fseek(3p), fsetpos(3p), stdio.h(0p).