NAME
fgetpos, fseek,
fseeko, fsetpos,
ftell, ftello,
rewind —
reposition a stream
LIBRARY
library “libc”
SYNOPSIS
#include
<stdio.h>
int
fseek(FILE
*stream, long int
offset, int
whence);
int
fseeko(FILE
*stream, off_t
offset, int
whence);
long int
ftell(FILE
*stream);
off_t
ftello(FILE
*stream);
void
rewind(FILE
*stream);
int
fgetpos(FILE
* restrict stream, fpos_t
* restrict pos);
int
fsetpos(FILE
* restrict stream, const
fpos_t * restrict pos);
DESCRIPTION
Thefseek()
function sets the file position indicator for the stream pointed to by
stream. The new position, measured in bytes, is obtained
by adding offset bytes to the position specified by
whence. If whence is set to
SEEK_SET, SEEK_CUR, or
SEEK_END, the offset is relative to the start of the
file, the current position indicator, or end-of-file, respectively. A
successful call to the fseek() function clears the
end-of-file indicator for the stream and undoes any effects of the
ungetc(3) function on the same stream.
The
fseeko()
function is identical to the fseek() function except
that the offset argument is of type
off_t.
The
ftell()
function obtains the current value of the file position indicator for the
stream pointed to by stream.
The
ftello()
function is identical to the ftell() function except
that the return value is of type off_t.
The
rewind()
function sets the file position indicator for the stream pointed to by
stream to the beginning of the file. It is equivalent
to:
(void)fseek(stream, 0L,
SEEK_SET)except that the error indicator for the stream is also cleared (see clearerr(3)).
In this implementations,
“fpos_t” is a complex object that
represents both the position and the parse state of the stream, making these
routines as the only way to portably reposition a text stream. The
pos argument of
fsetpos()
must always be initialized by a call to
fgetpos().
RETURN VALUES
The rewind() function returns no
value.
Upon successful completion, fgetpos(),
fseek(), fseeko(), and
fsetpos() return 0, whereas the functions
ftell() and ftello() return
the current offset. On failure, fseek(),
fseeko(), ftell(), and
ftello() return -1, while
fgetpos() and fsetpos()
return a nonzero value.
On error all functions set the global variable
errno to indicate the error. Since the
rewind() function does not return an error code,
applications need to clear errno before calling it in
order to detect errors.
ERRORS
- [
EBADF] - The stream specified is not a seekable stream.
- [
EINVAL] - The whence argument to
fseek() was notSEEK_SET,SEEK_END, orSEEK_CUR. - [
EOVERFLOW] - For
ftell(), the current file offset cannot be represented correctly in an object of type long.
The function fgetpos(),
fseek(), fseeko(),
fsetpos(), ftell(),
ftello(), and rewind() may
also fail and set errno for any of the errors
specified for the routines
fflush(3),
fstat(2), lseek(2), and
malloc(3).
SEE ALSO
STANDARDS
The fgetpos(),
fsetpos(), fseek(),
ftell(), and rewind()
functions conform to ANSI X3.159-1989
(“ANSI C89”). The
fseeko() and ftello()
functions conform to X/Open System Interfaces and Headers
Issue 5 (“XSH5”).
BUGS
The fgetpos() and
fsetpos() functions don't store/set shift states of
the stream in this implementation.