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.\" 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.\" @(#)rand.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd December 14, 2019 36.Dt RAND 3 37.Os 38.Sh NAME 39.Nm rand , 40.Nm srand , 41.Nm rand_r 42.Nd bad random number generator 43.Sh LIBRARY 44.Lb libc 45.Sh SYNOPSIS 46.In stdlib.h 47.Ft void 48.Fn srand "unsigned seed" 49.Ft int 50.Fn rand void 51.Ft int 52.Fn rand_r "unsigned *ctx" 53.Sh DESCRIPTION 54.Bf -symbolic 55The functions described in this manual page are not cryptographically 56secure. 57Applications which require unpredictable random numbers should use 58.Xr arc4random 3 59instead. 60.Ef 61.Pp 62These interfaces are obsoleted by 63.Xr random 3 . 64.Pp 65The 66.Fn rand 67function computes a sequence of pseudo-random integers in the range 68of 0 to 69.Dv RAND_MAX 70(as defined by the header file 71.In stdlib.h ) . 72.Pp 73The 74.Fn srand 75function sets its argument 76.Fa seed 77as the seed for a new sequence of 78pseudo-random numbers to be returned by 79.Fn rand . 80These sequences are repeatable by calling 81.Fn srand 82with the same seed value. 83.Pp 84If no 85.Fa seed 86value is provided, the functions are automatically 87seeded with a value of 1. 88.Pp 89The 90.Fn rand_r 91function 92provides the same functionality as 93.Fn rand . 94A pointer to the context value 95.Fa ctx 96must be supplied by the caller. 97.Pp 98For better generator quality, use 99.Xr random 3 100or 101.Xr lrand48 3 . 102.Sh SEE ALSO 103.Xr arc4random 3 , 104.Xr lrand48 3 , 105.Xr random 3 , 106.Xr random 4 107.Sh STANDARDS 108The 109.Fn rand 110and 111.Fn srand 112functions 113conform to 114.St -isoC . 115.Pp 116The 117.Fn rand_r 118function is marked as obsolescent in POSIX and may be removed in a future 119revision of the standard. 120