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.\" $FreeBSD$ 38.\" 39.Dd March 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 LIBRARY 52.Lb libc 53.Sh SYNOPSIS 54.In stdio.h 55.Ft int 56.Fn fseek "FILE *stream" "long offset" "int whence" 57.Ft long 58.Fn ftell "FILE *stream" 59.Ft void 60.Fn rewind "FILE *stream" 61.Ft int 62.Fn fgetpos "FILE *stream" "fpos_t *pos" 63.Ft int 64.Fn fsetpos "FILE *stream" "const fpos_t *pos" 65.In sys/types.h 66.Ft int 67.Fn fseeko "FILE *stream" "off_t offset" "int whence" 68.Ft off_t 69.Fn ftello "FILE *stream" 70.Sh DESCRIPTION 71The 72.Fn fseek 73function sets the file position indicator for the stream pointed 74to by 75.Fa stream . 76The new position, measured in bytes, is obtained by adding 77.Fa offset 78bytes to the position specified by 79.Fa whence . 80If 81.Fa whence 82is set to 83.Dv SEEK_SET , 84.Dv SEEK_CUR , 85or 86.Dv SEEK_END , 87the offset is relative to the 88start of the file, the current position indicator, or end-of-file, 89respectively. 90A successful call to the 91.Fn fseek 92function clears the end-of-file indicator for the stream and undoes 93any effects of the 94.Xr ungetc 3 95function on the same stream. 96.Pp 97The 98.Fn ftell 99function 100obtains the current value of the file position indicator for the 101stream pointed to by 102.Fa stream . 103.Pp 104The 105.Fn rewind 106function sets the file position indicator for the stream pointed 107to by 108.Fa stream 109to the beginning of the file. 110It is equivalent to: 111.Pp 112.Dl (void)fseek(stream, 0L, SEEK_SET) 113.Pp 114except that the error indicator for the stream is also cleared 115(see 116.Xr clearerr 3 ) . 117.Pp 118Since 119.Fn rewind 120does not return a value, 121an application wishing to detect errors should clear 122.Va errno , 123then call 124.Fn rewind , 125and if 126.Va errno 127is non-zero, assume an error has occurred. 128.Pp 129The 130.Fn fseeko 131function is identical to 132.Fn fseek , 133except it takes an 134.Fa off_t 135argument 136instead of a 137.Fa long . 138Likewise, the 139.Fn ftello 140function is identical to 141.Fn ftell , 142except it returns an 143.Fa off_t . 144.Pp 145The 146.Fn fgetpos 147and 148.Fn fsetpos 149functions 150are alternate interfaces equivalent to 151.Fn ftell 152and 153.Fn fseek 154(with whence set to 155.Dv SEEK_SET ) , 156setting and storing the current value of 157the file offset into or from the object referenced by 158.Fa pos . 159On some 160.Pq non- Ns Tn UNIX 161systems an 162.Dq Fa fpos_t 163object may be a complex object 164and these routines may be the only way to portably reposition a text stream. 165.Sh RETURN VALUES 166The 167.Fn rewind 168function 169returns no value. 170.Pp 171.Rv -std fgetpos fseek fseeko fsetpos 172.Pp 173Upon successful completion, 174.Fn ftell 175and 176.Fn ftello 177return the current offset. 178Otherwise, \-1 is returned and the global variable 179.Va errno 180is set to indicate the error. 181.Sh ERRORS 182.Bl -tag -width Er 183.It Bq Er EBADF 184The 185.Fa stream 186specified 187is not a seekable stream. 188.It Bq Er EINVAL 189The 190.Fa whence 191argument is invalid or 192the resulting file-position 193indicator would be set to a negative value. 194.It Bq Er EOVERFLOW 195The resulting file offset would be a value which 196cannot be represented correctly in an object of type 197.Fa off_t 198for 199.Fn fseeko 200and 201.Fn ftello 202or 203.Fa long 204for 205.Fn fseek 206and 207.Fn ftell . 208.It Bq Er ESPIPE 209The file descriptor underlying stream is associated with a pipe or FIFO 210or file-position indicator value is unspecified 211(see 212.Xr ungetc 3 ) . 213.El 214.Pp 215The functions 216.Fn fgetpos , 217.Fn fseek , 218.Fn fseeko , 219.Fn fsetpos , 220.Fn ftell , 221and 222.Fn ftello 223may also fail and set 224.Va errno 225for any of the errors specified for the routines 226.Xr fflush 3 , 227.Xr fstat 2 , 228.Xr lseek 2 , 229and 230.Xr malloc 3 . 231.Sh SEE ALSO 232.Xr lseek 2 , 233.Xr clearerr 3 , 234.Xr ungetc 3 235.Sh STANDARDS 236The 237.Fn fgetpos , 238.Fn fsetpos , 239.Fn fseek , 240.Fn ftell , 241and 242.Fn rewind 243functions 244conform to 245.St -isoC . 246.Pp 247The 248.Fn fseeko 249and 250.Fn ftello 251functions conform to 252.St -susv2 . 253