248 lines
5.4 KiB
Groff
248 lines
5.4 KiB
Groff
.\" $NetBSD: fseek.3,v 1.28 2017/01/01 12:39:33 abhinav Exp $
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.\"
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.\" 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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.\"
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.Dd January 1, 2017
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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 int offset" "int whence"
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.Ft int
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.Fn fseeko "FILE *stream" "off_t offset" "int whence"
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.Ft long int
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.Fn ftell "FILE *stream"
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.Ft off_t
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.Fn ftello "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 * restrict stream" "const fpos_t * restrict pos"
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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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function on the same stream.
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.Pp
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The
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.Fn fseeko
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function is identical to the
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.Fn fseek
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function except that the
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.Fa offset
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argument is of type
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.Fa off_t .
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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 ftello
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function is identical to the
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.Fn ftell
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function except that the return value is of type
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.Fa off_t .
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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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In this implementations,
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.Dq Fa fpos_t
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is a complex object that represents both the position and the parse
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state of the stream, making these routines as the only way to portably
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reposition a text stream.
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The
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.Ar pos
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argument of
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.Fn fsetpos
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must always be initialized by
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a call to
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.Fn fgetpos .
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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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Upon successful completion,
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.Fn fgetpos ,
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.Fn fseek ,
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.Fn fseeko ,
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and
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.Fn fsetpos
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return 0,
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whereas the functions
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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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On failure,
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.Fn fseek ,
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.Fn fseeko ,
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.Fn ftell ,
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and
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.Fn ftello
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return \-1, while
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.Fn fgetpos
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and
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.Fn fsetpos
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return a nonzero value.
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.Pp
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On error all functions set the global variable
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.Va errno
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to indicate the error.
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Since the
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.Fn rewind
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function does not return an error code, applications need to clear
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.Va errno
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before calling it in order to detect errors.
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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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specified
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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 to
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.Fn fseek
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was not
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.Dv SEEK_SET ,
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.Dv SEEK_END ,
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or
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.Dv SEEK_CUR .
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.It Bq Er EOVERFLOW
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For
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.Fn ftell ,
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the current file offset cannot be represented correctly in an object of type
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.Fa long .
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.El
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.Pp
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The function
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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 ungetc 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 -ansiC .
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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 -xsh5 .
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.Sh BUGS
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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 don't store/set shift states of the stream in this implementation.
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