Libc-763.13.tar.gz

[apple/libc.git] / stdlib / rand.3

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.\"     @(#)rand.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/stdlib/rand.3,v 1.16 2007/01/09 00:28:10 imp Exp $
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.Dd May 25, 1999
.Dt RAND 3
.Os
.Sh NAME
.Nm rand ,
.Nm rand_r ,
.Nm srand ,
.Nm sranddev
.Nd bad random number generator
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fo rand
.Fa void
.Fc
.Ft int
.Fo rand_r
.Fa "unsigned *seed"
.Fc
.Ft void
.Fo srand
.Fa "unsigned seed"
.Fc
.Ft void
.Fo sranddev
.Fa void
.Fc
.Sh DESCRIPTION
.Bf -symbolic
These interfaces are obsoleted by
.Xr random 3 .
.Ef
.Pp
The
.Fn rand
function computes a sequence of pseudo-random integers in the range
of 0 to
.Dv RAND_MAX
(as defined by the header file
.In stdlib.h ) .
.Pp
The
.Fn srand
function sets its argument
.Fa seed
as the seed for a new sequence of
pseudo-random numbers to be returned by
.Fn rand .
These sequences are repeatable by calling
.Fn srand
with the same seed value.
.Pp
If no
.Fa seed
value is provided, the functions are automatically
seeded with a value of 1.
.Pp
The
.Fn sranddev
function initializes a seed, using the
.Xr random 4
random number device which returns good random numbers.
However, the
.Fn rand
function still remains unsuitable for cryptographic use.
.Pp
The
.Fn rand_r
function
provides the same functionality as
.Fn rand .
A pointer to the context value
.Fa seed
must be supplied by the caller.
.Sh SEE ALSO
.Xr random 3 ,
.Xr random 4
.Sh STANDARDS
The
.Fn rand
and
.Fn srand
functions
conform to
.St -isoC .
.Pp
The
.Fn rand_r
function is as proposed in the POSIX.4a Draft #6 document.