.\" 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: src/lib/libc/stdio/fseek.3,v 1.25 2004/03/20 08:38:27 tjr Exp $ .\" .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 .Fo fgetpos .Fa "FILE *restrict stream" .Fa "fpos_t *restrict pos" .Fc .Ft int .Fo fseek .Fa "FILE *stream" .Fa "long offset" .Fa "int whence" .Fc .Ft int .Fo fseeko .Fa "FILE *stream" .Fa "off_t offset" .Fa "int whence" .Fc .Ft int .Fo fsetpos .Fa "FILE *stream" .Fa "const fpos_t *pos" .Fc .Ft long .Fo ftell .Fa "FILE *stream" .Fc .Ft off_t .Fo ftello .Fa "FILE *stream" .Fc .Ft void .Fo rewind .Fa "FILE *stream" .Fc .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 LEGACY SYNOPSIS .Fd #include <stdio.h> .Fd #include <sys/types.h> .Pp .Ft int .br .Fo fseeko .Fa "FILE *stream" .Fa "off_t offset" .Fa "int whence" .Fc ; .Pp The include file .In sys/types.h supplies the definition for .Vt off_t . .Sh SEE ALSO .Xr lseek 2 , .Xr clearerr 3 , .Xr fwide 3 , .Xr ungetc 3 , .Xr ungetwc 3 , .Xr compat 5 .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 .