stdlib/rand.3

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  32 .\"     @(#)rand.3      8.1 (Berkeley) 6/4/93
  33 .\" $FreeBSD: src/lib/libc/stdlib/rand.3,v 1.16 2007/01/09 00:28:10 imp Exp $
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  35 .Dd May 25, 1999
  36 .Dt RAND 3
  37 .Os
  38 .Sh NAME
  39 .Nm rand ,
  40 .Nm rand_r ,
  41 .Nm srand ,
  42 .Nm sranddev
  43 .Nd bad random number generator
  44 .Sh LIBRARY
  45 .Lb libc
  46 .Sh SYNOPSIS
  47 .In stdlib.h
  48 .Ft int
  49 .Fo rand
  50 .Fa void
  51 .Fc
  52 .Ft int
  53 .Fo rand_r
  54 .Fa "unsigned *seed"
  55 .Fc
  56 .Ft void
  57 .Fo srand
  58 .Fa "unsigned seed"
  59 .Fc
  60 .Ft void
  61 .Fo sranddev
  62 .Fa void
  63 .Fc
  64 .Sh DESCRIPTION
  65 .Bf -symbolic
  66 These interfaces are obsoleted by
  67 .Xr random 3 .
  68 .Ef
  69 .Pp
  70 The
  71 .Fn rand
  72 function computes a sequence of pseudo-random integers in the range
  73 of 0 to
  74 .Dv RAND_MAX
  75 (as defined by the header file
  76 .In stdlib.h ) .
  77 .Pp
  78 The
  79 .Fn srand
  80 function sets its argument
  81 .Fa seed
  82 as the seed for a new sequence of
  83 pseudo-random numbers to be returned by
  84 .Fn rand .
  85 These sequences are repeatable by calling
  86 .Fn srand
  87 with the same seed value.
  88 .Pp
  89 If no
  90 .Fa seed
  91 value is provided, the functions are automatically
  92 seeded with a value of 1.
  93 .Pp
  94 The
  95 .Fn sranddev
  96 function initializes a seed, using the
  97 .Xr random 4
  98 random number device which returns good random numbers.
  99 However, the
 100 .Fn rand
 101 function still remains unsuitable for cryptographic use.
 102 .Pp
 103 The
 104 .Fn rand_r
 105 function
 106 provides the same functionality as
 107 .Fn rand .
 108 A pointer to the context value
 109 .Fa seed
 110 must be supplied by the caller.
 111 .Sh SEE ALSO
 112 .Xr random 3 ,
 113 .Xr random 4
 114 .Sh STANDARDS
 115 The
 116 .Fn rand
 117 and
 118 .Fn srand
 119 functions
 120 conform to
 121 .St -isoC .
 122 .Pp
 123 The
 124 .Fn rand_r
 125 function is as proposed in the POSIX.4a Draft #6 document.