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. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the University of 19.\" California, Berkeley and its contributors. 20.\" 4. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.\" @(#)fseek.3 8.1 (Berkeley) 6/4/93 37.\" $Id$ 38.\" 39.Dd Mar 5, 1999 40.Dt FSEEK 3 41.Os 42.Sh NAME 43.Nm fgetpos , 44.Nm fseek , 45.Nm fseeko , 46.Nm fsetpos , 47.Nm ftell , 48.Nm ftello , 49.Nm rewind 50.Nd reposition a stream 51.Sh SYNOPSIS 52.Fd #include <stdio.h> 53.Ft int 54.Fn fseek "FILE *stream" "long offset" "int whence" 55.Ft long 56.Fn ftell "FILE *stream" 57.Ft void 58.Fn rewind "FILE *stream" 59.Ft int 60.Fn fgetpos "FILE *stream" "fpos_t *pos" 61.Ft int 62.Fn fsetpos "FILE *stream" "const fpos_t *pos" 63.Fd #include <sys/types.h> 64.Ft int 65.Fn fseeko "FILE *stream" "off_t offset" "int whence" 66.Ft off_t 67.Fn ftello "FILE *stream" 68.Sh DESCRIPTION 69The 70.Fn fseek 71function sets the file position indicator for the stream pointed 72to by 73.Fa stream . 74The new position, measured in bytes, is obtained by adding 75.Fa offset 76bytes to the position specified by 77.Fa whence . 78If 79.Fa whence 80is set to 81.Dv SEEK_SET , 82.Dv SEEK_CUR , 83or 84.Dv SEEK_END , 85the offset is relative to the 86start of the file, the current position indicator, or end-of-file, 87respectively. 88A successful call to the 89.Fn fseek 90function clears the end-of-file indicator for the stream and undoes 91any effects of the 92.Xr ungetc 3 93function on the same stream. 94.Pp 95The 96.Fn ftell 97function 98obtains the current value of the file position indicator for the 99stream pointed to by 100.Fa stream . 101.Pp 102The 103.Fn rewind 104function sets the file position indicator for the stream pointed 105to by 106.Fa stream 107to the beginning of the file. 108It is equivalent to: 109.Pp 110.Dl (void)fseek(stream, 0L, SEEK_SET) 111.Pp 112except that the error indicator for the stream is also cleared 113(see 114.Xr clearerr 3 ) . 115.Pp 116The 117.Fn fseeko 118function is identical to 119.Fn fseek , 120except it takes an 121.Fa off_t 122argument 123instead of a 124.Fa long . 125Likewise, the 126.Fn ftello 127function is identical to 128.Fn ftell , 129except it returns an 130.Fa off_t . 131.Pp 132The 133.Fn fgetpos 134and 135.Fn fsetpos 136functions 137are alternate interfaces equivalent to 138.Fn ftell 139and 140.Fn fseek 141(with whence set to 142.Dv SEEK_SET ) , 143setting and storing the current value of 144the file offset into or from the object referenced by 145.Fa pos . 146On some 147.Pq non- Ns Tn UNIX 148systems an 149.Dq Fa fpos_t 150object may be a complex object 151and these routines may be the only way to portably reposition a text stream. 152.Sh RETURN VALUES 153The 154.Fn rewind 155function 156returns no value. 157Upon successful completion, 158.Fn fgetpos , 159.Fn fseek , 160.Fn fseeko , 161and 162.Fn fsetpos 163return 0, 164and 165.Fn ftell 166and 167.Fn ftello 168return the current offset. 169Otherwise, \-1 is returned and the global variable errno is set to 170indicate the error. 171.Sh ERRORS 172.Bl -tag -width [EINVAL] 173.It Bq Er EBADF 174The 175.Fa stream 176specified 177is not a seekable stream. 178.It Bq Er EINVAL 179The 180.Fa whence 181argument to 182.Fn fseek 183was not 184.Dv SEEK_SET , 185.Dv SEEK_END , 186or 187.Dv SEEK_CUR . 188.It Bq Er EOVERFLOW 189For 190.Fn ftell , 191the resulting file offset would be a value which 192cannot be represented correctly in an object of type long. 193.El 194.Pp 195The functions 196.Fn fgetpos , 197.Fn fseek , 198.Fn fseeko , 199.Fn fsetpos , 200.Fn ftell , 201and 202.Fn ftello 203may also fail and set 204.Va errno 205for any of the errors specified for the routines 206.Xr fflush 3 , 207.Xr fstat 2 , 208.Xr lseek 2 , 209and 210.Xr malloc 3 . 211.Sh SEE ALSO 212.Xr lseek 2 213.Sh STANDARDS 214The 215.Fn fgetpos , 216.Fn fsetpos , 217.Fn fseek , 218.Fn ftell , 219and 220.Fn rewind 221functions 222conform to 223.St -ansiC . 224.Pp 225The 226.Fn fseeko 227and 228.Fn ftello 229functions conform to 230.St -susv2 . 231