7e6cabd06e
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
270 lines
6.0 KiB
Groff
270 lines
6.0 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek and the American National Standards Committee X3,
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.\" on Information Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)fseek.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd March 19, 2004
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.Dt FSEEK 3
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.Os
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.Sh NAME
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.Nm fgetpos ,
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.Nm fseek ,
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.Nm fseeko ,
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.Nm fsetpos ,
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.Nm ftell ,
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.Nm ftello ,
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.Nm rewind
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.Nd reposition a stream
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdio.h
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.Ft int
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.Fn fseek "FILE *stream" "long offset" "int whence"
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.Ft long
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.Fn ftell "FILE *stream"
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.Ft void
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.Fn rewind "FILE *stream"
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.Ft int
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.Fn fgetpos "FILE * restrict stream" "fpos_t * restrict pos"
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.Ft int
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.Fn fsetpos "FILE *stream" "const fpos_t *pos"
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.In sys/types.h
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.Ft int
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.Fn fseeko "FILE *stream" "off_t offset" "int whence"
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.Ft off_t
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.Fn ftello "FILE *stream"
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.Sh DESCRIPTION
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The
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.Fn fseek
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function sets the file position indicator for the stream pointed
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to by
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.Fa stream .
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The new position, measured in bytes, is obtained by adding
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.Fa offset
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bytes to the position specified by
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.Fa whence .
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If
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.Fa whence
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is set to
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.Dv SEEK_SET ,
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.Dv SEEK_CUR ,
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or
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.Dv SEEK_END ,
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the offset is relative to the
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start of the file, the current position indicator, or end-of-file,
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respectively.
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A successful call to the
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.Fn fseek
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function clears the end-of-file indicator for the stream and undoes
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any effects of the
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.Xr ungetc 3
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and
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.Xr ungetwc 3
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functions on the same stream.
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.Pp
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The
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.Fn ftell
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function
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obtains the current value of the file position indicator for the
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stream pointed to by
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.Fa stream .
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.Pp
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The
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.Fn rewind
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function sets the file position indicator for the stream pointed
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to by
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.Fa stream
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to the beginning of the file.
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It is equivalent to:
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.Pp
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.Dl (void)fseek(stream, 0L, SEEK_SET)
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.Pp
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except that the error indicator for the stream is also cleared
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(see
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.Xr clearerr 3 ) .
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.Pp
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Since
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.Fn rewind
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does not return a value,
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an application wishing to detect errors should clear
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.Va errno ,
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then call
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.Fn rewind ,
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and if
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.Va errno
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is non-zero, assume an error has occurred.
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.Pp
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The
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.Fn fseeko
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function is identical to
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.Fn fseek ,
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except it takes an
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.Fa off_t
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argument
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instead of a
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.Fa long .
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Likewise, the
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.Fn ftello
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function is identical to
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.Fn ftell ,
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except it returns an
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.Fa off_t .
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.Pp
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The
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.Fn fgetpos
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and
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.Fn fsetpos
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functions
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are alternate interfaces for retrieving and setting the current position in
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the file, similar to
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.Fn ftell
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and
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.Fn fseek ,
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except that the current position is stored in an opaque object of
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type
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.Vt fpos_t
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pointed to by
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.Fa pos .
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These functions provide a portable way to seek to offsets larger than
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those that can be represented by a
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.Vt long int .
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They may also store additional state information in the
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.Vt fpos_t
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object to facilitate seeking within files containing multibyte
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characters with state-dependent encodings.
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Although
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.Vt fpos_t
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has traditionally been an integral type,
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applications cannot assume that it is;
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in particular, they must not perform arithmetic on objects
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of this type.
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.Pp
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If the stream is a wide character stream (see
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.Xr fwide 3 ) ,
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the position specified by the combination of
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.Fa offset
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and
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.Fa whence
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must contain the first byte of a multibyte sequence.
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.Sh RETURN VALUES
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The
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.Fn rewind
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function
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returns no value.
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.Pp
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.Rv -std fgetpos fseek fseeko fsetpos
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.Pp
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Upon successful completion,
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.Fn ftell
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and
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.Fn ftello
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return the current offset.
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Otherwise, \-1 is returned and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa stream
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argument
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is not a seekable stream.
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.It Bq Er EINVAL
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The
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.Fa whence
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argument is invalid or
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the resulting file-position
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indicator would be set to a negative value.
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.It Bq Er EOVERFLOW
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The resulting file offset would be a value which
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cannot be represented correctly in an object of type
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.Fa off_t
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for
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.Fn fseeko
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and
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.Fn ftello
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or
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.Fa long
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for
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.Fn fseek
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and
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.Fn ftell .
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.It Bq Er ESPIPE
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The file descriptor underlying stream is associated with a pipe or FIFO
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or file-position indicator value is unspecified
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(see
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.Xr ungetc 3 ) .
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.El
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.Pp
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The functions
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.Fn fgetpos ,
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.Fn fseek ,
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.Fn fseeko ,
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.Fn fsetpos ,
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.Fn ftell ,
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.Fn ftello ,
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and
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.Fn rewind
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may also fail and set
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.Va errno
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for any of the errors specified for the routines
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.Xr fflush 3 ,
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.Xr fstat 2 ,
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.Xr lseek 2 ,
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and
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.Xr malloc 3 .
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.Sh SEE ALSO
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.Xr lseek 2 ,
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.Xr clearerr 3 ,
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.Xr fwide 3 ,
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.Xr ungetc 3 ,
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.Xr ungetwc 3
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.Sh STANDARDS
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The
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.Fn fgetpos ,
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.Fn fsetpos ,
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.Fn fseek ,
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.Fn ftell ,
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and
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.Fn rewind
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functions
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conform to
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.St -isoC .
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.Pp
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The
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.Fn fseeko
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and
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.Fn ftello
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functions conform to
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.St -p1003.1-2001 .
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