NAME
ftell ftello
— return a file offset in a stream
SYNOPSIS
#include
<stdio.h>
long ftell(FILE *stream); [CX] off_t ftello(FILE *stream);
DESCRIPTION
[CX] 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.
[CX] 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.
RETURN VALUE
Upon successful completion, ftell ()
[CX] 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.
ERRORS
The ftell () [CX] and
ftello () functions shall fail if:
- [EBADF]
- [CX] The file descriptor underlying stream is not an open file descriptor.
- [EOVERFLOW]
- [CX] For
ftell(), the current file offset cannot be represented correctly in an object of type long . - [EOVERFLOW]
- [CX] For ftello (), the current file offset cannot be represented correctly in an object of type off_t .
- [ESPIPE]
- [CX] The file descriptor underlying stream is associated with a pipe, FIFO, or socket.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
V2_chap02(3), fgetpos(3), fopen(3), fseek(3), lseek(3)
XBD <stdio.h>
CHANGE HISTORY
First released in Issue 1. Derived from Issue 1 of the SVID.
Issue 5
Large File Summit extensions are added.
Issue 6
Extensions beyond the ISO C standard are marked.
The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:
- The ftello () function is added.
- The [EOVERFLOW] error conditions are added.
An additional [ESPIPE] error condition is added for sockets.
Issue 7
POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0204 [105], XSH/TC1-2008/0205 [421], XSH/TC1-2008/0206 [122], XSH/TC1-2008/0207 [122], and XSH/TC1-2008/0208 [14] are applied.