1.\" Copyright (c) 1990, 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the American National Standards Committee X3, on Information 6.\" 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.\" $OpenBSD: rand.3,v 1.16 2014/07/17 23:12:28 deraadt Exp $ 33.\" 34.Dd $Mdocdate: July 17 2014 $ 35.Dt RAND 3 36.Os 37.Sh NAME 38.Nm rand , 39.Nm rand_r , 40.Nm srand 41.Nd bad random number generator 42.Sh SYNOPSIS 43.In stdlib.h 44.Ft void 45.Fn srand "unsigned int seed" 46.Ft int 47.Fn rand void 48.Ft int 49.Fn rand_r "unsigned int *seed" 50.Sh DESCRIPTION 51.Bf -symbolic 52These interfaces are obsoleted by 53.Xr random 3 , 54which is also unsafe. 55Consider using 56.Xr arc4random 3 . 57.Ef 58.Pp 59The 60.Fn rand 61function computes a sequence of pseudo-random integers in the range 62of 0 to 63.Dv RAND_MAX 64(as defined by the header file 65.In stdlib.h ) . 66.Pp 67The 68.Fn srand 69function sets its argument as the seed for a new sequence of 70pseudo-random numbers to be returned by 71.Fn rand . 72These sequences are repeatable by calling 73.Fn srand 74with the same seed value. 75.Pp 76If no seed value is provided, the functions are automatically 77seeded with a value of 1. 78.Pp 79The 80.Fn rand_r 81is a thread-safe version of 82.Fn rand . 83Storage for the seed must be provided through the 84.Fa seed 85argument, and needs to have been initialized by the caller. 86.Sh SEE ALSO 87.Xr arc4random 3 , 88.Xr rand48 3 , 89.Xr random 3 90.Sh STANDARDS 91The 92.Fn rand 93and 94.Fn srand 95functions conform to 96.St -ansiC . 97.Pp 98The 99.Fn rand_r 100function conforms to 101.St -p1003.1-2008 . 102.Sh HISTORY 103The functions 104.Fn rand 105and 106.Fn srand 107first appeared in 108.At v3 . 109