1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Chris Torek and the American National Standards Committee X3, 6.\" on Information Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)fseek.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD: src/lib/libc/stdio/fseek.3,v 1.27 2007/06/18 02:13:04 ache Exp $ 34.\" $DragonFly: src/lib/libc/stdio/fseek.3,v 1.3 2007/07/30 22:11:33 swildner Exp $ 35.\" 36.Dd March 19, 2004 37.Dt FSEEK 3 38.Os 39.Sh NAME 40.Nm fgetpos , 41.Nm fseek , 42.Nm fseeko , 43.Nm fsetpos , 44.Nm ftell , 45.Nm ftello , 46.Nm rewind 47.Nd reposition a stream 48.Sh LIBRARY 49.Lb libc 50.Sh SYNOPSIS 51.In stdio.h 52.Ft int 53.Fn fseek "FILE *stream" "long offset" "int whence" 54.Ft long 55.Fn ftell "FILE *stream" 56.Ft void 57.Fn rewind "FILE *stream" 58.Ft int 59.Fn fgetpos "FILE * restrict stream" "fpos_t * restrict pos" 60.Ft int 61.Fn fsetpos "FILE *stream" "const fpos_t *pos" 62.In sys/types.h 63.Ft int 64.Fn fseeko "FILE *stream" "off_t offset" "int whence" 65.Ft off_t 66.Fn ftello "FILE *stream" 67.Sh DESCRIPTION 68The 69.Fn fseek 70function sets the file position indicator for the stream pointed 71to by 72.Fa stream . 73The new position, measured in bytes, is obtained by adding 74.Fa offset 75bytes to the position specified by 76.Fa whence . 77If 78.Fa whence 79is set to 80.Dv SEEK_SET , 81.Dv SEEK_CUR , 82or 83.Dv SEEK_END , 84the offset is relative to the 85start of the file, the current position indicator, or end-of-file, 86respectively. 87A successful call to the 88.Fn fseek 89function clears the end-of-file indicator for the stream and undoes 90any effects of the 91.Xr ungetc 3 92and 93.Xr ungetwc 3 94functions on the same stream. 95.Pp 96The 97.Fn ftell 98function 99obtains the current value of the file position indicator for the 100stream pointed to by 101.Fa stream . 102.Pp 103The 104.Fn rewind 105function sets the file position indicator for the stream pointed 106to by 107.Fa stream 108to the beginning of the file. 109It is equivalent to: 110.Pp 111.Dl (void)fseek(stream, 0L, SEEK_SET) 112.Pp 113except that the error indicator for the stream is also cleared 114(see 115.Xr clearerr 3 ) . 116.Pp 117Since 118.Fn rewind 119does not return a value, 120an application wishing to detect errors should clear 121.Va errno , 122then call 123.Fn rewind , 124and if 125.Va errno 126is non-zero, assume an error has occurred. 127.Pp 128The 129.Fn fseeko 130function is identical to 131.Fn fseek , 132except it takes an 133.Fa off_t 134argument 135instead of a 136.Fa long . 137Likewise, the 138.Fn ftello 139function is identical to 140.Fn ftell , 141except it returns an 142.Fa off_t . 143.Pp 144The 145.Fn fgetpos 146and 147.Fn fsetpos 148functions 149are alternate interfaces for retrieving and setting the current position in 150the file, similar to 151.Fn ftell 152and 153.Fn fseek , 154except that the current position is stored in an opaque object of 155type 156.Vt fpos_t 157pointed to by 158.Fa pos . 159These functions provide a portable way to seek to offsets larger than 160those that can be represented by a 161.Vt long int . 162They may also store additional state information in the 163.Vt fpos_t 164object to facilitate seeking within files containing multibyte 165characters with state-dependent encodings. 166Although 167.Vt fpos_t 168has traditionally been an integral type, 169applications cannot assume that it is; 170in particular, they must not perform arithmetic on objects 171of this type. 172.Pp 173If the stream is a wide character stream (see 174.Xr fwide 3 ) , 175the position specified by the combination of 176.Fa offset 177and 178.Fa whence 179must contain the first byte of a multibyte sequence. 180.Sh RETURN VALUES 181The 182.Fn rewind 183function 184returns no value. 185.Pp 186.Rv -std fgetpos fseek fseeko fsetpos 187.Pp 188Upon successful completion, 189.Fn ftell 190and 191.Fn ftello 192return the current offset. 193Otherwise, \-1 is returned and the global variable 194.Va errno 195is set to indicate the error. 196.Sh ERRORS 197.Bl -tag -width Er 198.It Bq Er EBADF 199The 200.Fa stream 201argument 202is not a seekable stream. 203.It Bq Er EINVAL 204The 205.Fa whence 206argument is invalid or 207the resulting file-position 208indicator would be set to a negative value. 209.It Bq Er EOVERFLOW 210The resulting file offset would be a value which 211cannot be represented correctly in an object of type 212.Fa off_t 213for 214.Fn fseeko 215and 216.Fn ftello 217or 218.Fa long 219for 220.Fn fseek 221and 222.Fn ftell . 223.It Bq Er ESPIPE 224The file descriptor underlying stream is associated with a pipe or FIFO 225or file-position indicator value is unspecified 226(see 227.Xr ungetc 3 ) . 228.El 229.Pp 230The functions 231.Fn fgetpos , 232.Fn fseek , 233.Fn fseeko , 234.Fn fsetpos , 235.Fn ftell , 236.Fn ftello , 237and 238.Fn rewind 239may also fail and set 240.Va errno 241for any of the errors specified for the routines 242.Xr fflush 3 , 243.Xr fstat 2 , 244.Xr lseek 2 , 245and 246.Xr malloc 3 . 247.Sh SEE ALSO 248.Xr lseek 2 , 249.Xr clearerr 3 , 250.Xr fwide 3 , 251.Xr ungetc 3 , 252.Xr ungetwc 3 253.Sh STANDARDS 254The 255.Fn fgetpos , 256.Fn fsetpos , 257.Fn fseek , 258.Fn ftell , 259and 260.Fn rewind 261functions 262conform to 263.St -isoC . 264.Pp 265The 266.Fn fseeko 267and 268.Fn ftello 269functions conform to 270.St -p1003.1-2001 . 271