273 lines
6.3 KiB
Groff
273 lines
6.3 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to Berkeley by
|
|
.\" Chris Torek and the American National Standards Committee X3,
|
|
.\" on Information Processing Systems.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)fseek.3 8.1 (Berkeley) 6/4/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd March 19, 2004
|
|
.Dt FSEEK 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm fgetpos ,
|
|
.Nm fseek ,
|
|
.Nm fseeko ,
|
|
.Nm fsetpos ,
|
|
.Nm ftell ,
|
|
.Nm ftello ,
|
|
.Nm rewind
|
|
.Nd reposition a stream
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In stdio.h
|
|
.Ft int
|
|
.Fn fseek "FILE *stream" "long offset" "int whence"
|
|
.Ft long
|
|
.Fn ftell "FILE *stream"
|
|
.Ft void
|
|
.Fn rewind "FILE *stream"
|
|
.Ft int
|
|
.Fn fgetpos "FILE * restrict stream" "fpos_t * restrict pos"
|
|
.Ft int
|
|
.Fn fsetpos "FILE *stream" "const fpos_t *pos"
|
|
.In sys/types.h
|
|
.Ft int
|
|
.Fn fseeko "FILE *stream" "off_t offset" "int whence"
|
|
.Ft off_t
|
|
.Fn ftello "FILE *stream"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn fseek
|
|
function sets the file position indicator for the stream pointed
|
|
to by
|
|
.Fa stream .
|
|
The new position, measured in bytes, is obtained by adding
|
|
.Fa offset
|
|
bytes to the position specified by
|
|
.Fa whence .
|
|
If
|
|
.Fa whence
|
|
is set to
|
|
.Dv SEEK_SET ,
|
|
.Dv SEEK_CUR ,
|
|
or
|
|
.Dv 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
|
|
.Fn fseek
|
|
function clears the end-of-file indicator for the stream and undoes
|
|
any effects of the
|
|
.Xr ungetc 3
|
|
and
|
|
.Xr ungetwc 3
|
|
functions on the same stream.
|
|
.Pp
|
|
The
|
|
.Fn ftell
|
|
function
|
|
obtains the current value of the file position indicator for the
|
|
stream pointed to by
|
|
.Fa stream .
|
|
.Pp
|
|
The
|
|
.Fn rewind
|
|
function sets the file position indicator for the stream pointed
|
|
to by
|
|
.Fa stream
|
|
to the beginning of the file.
|
|
It is equivalent to:
|
|
.Pp
|
|
.Dl (void)fseek(stream, 0L, SEEK_SET)
|
|
.Pp
|
|
except that the error indicator for the stream is also cleared
|
|
(see
|
|
.Xr clearerr 3 ) .
|
|
.Pp
|
|
Since
|
|
.Fn rewind
|
|
does not return a value,
|
|
an application wishing to detect errors should clear
|
|
.Va errno ,
|
|
then call
|
|
.Fn rewind ,
|
|
and if
|
|
.Va errno
|
|
is non-zero, assume an error has occurred.
|
|
.Pp
|
|
The
|
|
.Fn fseeko
|
|
function is identical to
|
|
.Fn fseek ,
|
|
except it takes an
|
|
.Fa off_t
|
|
argument
|
|
instead of a
|
|
.Fa long .
|
|
Likewise, the
|
|
.Fn ftello
|
|
function is identical to
|
|
.Fn ftell ,
|
|
except it returns an
|
|
.Fa off_t .
|
|
.Pp
|
|
The
|
|
.Fn fgetpos
|
|
and
|
|
.Fn fsetpos
|
|
functions
|
|
are alternate interfaces for retrieving and setting the current position in
|
|
the file, similar to
|
|
.Fn ftell
|
|
and
|
|
.Fn fseek ,
|
|
except that the current position is stored in an opaque object of
|
|
type
|
|
.Vt fpos_t
|
|
pointed to by
|
|
.Fa pos .
|
|
These functions provide a portable way to seek to offsets larger than
|
|
those that can be represented by a
|
|
.Vt long int .
|
|
They may also store additional state information in the
|
|
.Vt fpos_t
|
|
object to facilitate seeking within files containing multibyte
|
|
characters with state-dependent encodings.
|
|
Although
|
|
.Vt fpos_t
|
|
has traditionally been an integral type,
|
|
applications cannot assume that it is;
|
|
in particular, they must not perform arithmetic on objects
|
|
of this type.
|
|
.Pp
|
|
If the stream is a wide character stream (see
|
|
.Xr fwide 3 ) ,
|
|
the position specified by the combination of
|
|
.Fa offset
|
|
and
|
|
.Fa whence
|
|
must contain the first byte of a multibyte sequence.
|
|
.Sh RETURN VALUES
|
|
The
|
|
.Fn rewind
|
|
function
|
|
returns no value.
|
|
.Pp
|
|
.Rv -std fgetpos fseek fseeko fsetpos
|
|
.Pp
|
|
Upon successful completion,
|
|
.Fn ftell
|
|
and
|
|
.Fn ftello
|
|
return the current offset.
|
|
Otherwise, \-1 is returned and the global variable
|
|
.Va errno
|
|
is set to indicate the error.
|
|
.Sh ERRORS
|
|
.Bl -tag -width Er
|
|
.It Bq Er EBADF
|
|
The
|
|
.Fa stream
|
|
argument
|
|
is not a seekable stream.
|
|
.It Bq Er EINVAL
|
|
The
|
|
.Fa whence
|
|
argument is invalid or
|
|
the resulting file-position
|
|
indicator would be set to a negative value.
|
|
.It Bq Er EOVERFLOW
|
|
The resulting file offset would be a value which
|
|
cannot be represented correctly in an object of type
|
|
.Fa off_t
|
|
for
|
|
.Fn fseeko
|
|
and
|
|
.Fn ftello
|
|
or
|
|
.Fa long
|
|
for
|
|
.Fn fseek
|
|
and
|
|
.Fn ftell .
|
|
.It Bq Er ESPIPE
|
|
The file descriptor underlying stream is associated with a pipe or FIFO
|
|
or file-position indicator value is unspecified
|
|
(see
|
|
.Xr ungetc 3 ) .
|
|
.El
|
|
.Pp
|
|
The functions
|
|
.Fn fgetpos ,
|
|
.Fn fseek ,
|
|
.Fn fseeko ,
|
|
.Fn fsetpos ,
|
|
.Fn ftell ,
|
|
and
|
|
.Fn ftello
|
|
may also fail and set
|
|
.Va errno
|
|
for any of the errors specified for the routines
|
|
.Xr fflush 3 ,
|
|
.Xr fstat 2 ,
|
|
.Xr lseek 2 ,
|
|
and
|
|
.Xr malloc 3 .
|
|
.Sh SEE ALSO
|
|
.Xr lseek 2 ,
|
|
.Xr clearerr 3 ,
|
|
.Xr fwide 3 ,
|
|
.Xr ungetc 3 ,
|
|
.Xr ungetwc 3
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn fgetpos ,
|
|
.Fn fsetpos ,
|
|
.Fn fseek ,
|
|
.Fn ftell ,
|
|
and
|
|
.Fn rewind
|
|
functions
|
|
conform to
|
|
.St -isoC .
|
|
.Pp
|
|
The
|
|
.Fn fseeko
|
|
and
|
|
.Fn ftello
|
|
functions conform to
|
|
.St -p1003.1-2001 .
|