269 lines
6.0 KiB
Groff
269 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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.\" 4. 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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and
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.Fn ftello
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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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