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.\" 4. 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 October 6, 2010 36.Dt RAND 3 37.Os 38.Sh NAME 39.Nm rand , 40.Nm srand , 41.Nm sranddev , 42.Nm rand_r 43.Nd bad random number generator 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In stdlib.h 48.Ft void 49.Fn srand "unsigned seed" 50.Ft void 51.Fn sranddev void 52.Ft int 53.Fn rand void 54.Ft int 55.Fn rand_r "unsigned *ctx" 56.Sh DESCRIPTION 57.Bf -symbolic 58These interfaces are obsoleted by 59.Xr random 3 . 60.Ef 61.Pp 62The 63.Fn rand 64function computes a sequence of pseudo-random integers in the range 65of 0 to 66.Dv RAND_MAX 67(as defined by the header file 68.In stdlib.h ) . 69.Pp 70The 71.Fn srand 72function sets its argument 73.Fa seed 74as the seed for a new sequence of 75pseudo-random numbers to be returned by 76.Fn rand . 77These sequences are repeatable by calling 78.Fn srand 79with the same seed value. 80.Pp 81If no 82.Fa seed 83value is provided, the functions are automatically 84seeded with a value of 1. 85.Pp 86The 87.Fn sranddev 88function initializes a seed using the 89.Xr random 4 90random number device which returns good random numbers. 91However, the 92.Fn rand 93function still remains unsuitable for cryptographic use. 94.Pp 95The 96.Fn rand_r 97function 98provides the same functionality as 99.Fn rand . 100A pointer to the context value 101.Fa ctx 102must be supplied by the caller. 103.Pp 104For better generator quality, use 105.Xr random 3 106or 107.Xr lrand48 3 . 108Applications requiring cryptographic quality randomness should use 109.Xr arc4random 3 . 110.Sh SEE ALSO 111.Xr arc4random 3 , 112.Xr lrand48 3 , 113.Xr random 3 , 114.Xr random 4 115.Sh STANDARDS 116The 117.Fn rand 118and 119.Fn srand 120functions 121conform to 122.St -isoC . 123.Pp 124The 125.Fn rand_r 126function is as proposed in the POSIX.4a Draft #6 document. 127