man3/random_r.3

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  26 .TH RANDOM_R 3  2016-03-15 "GNU" "Linux Programmer's Manual"
  27 .SH NAME
  28 random_r, srandom_r, initstate_r, setstate_r \- reentrant
  29 random number generator
  30 .SH SYNOPSIS
  31 .nf
  32 .B #include <stdlib.h>
  33 .sp
  34 .BI "int random_r(struct random_data *" buf ", int32_t *" result );
  35
  36 .BI "int srandom_r(unsigned int " seed ", struct random_data *" buf );
  37
  38 .BI "int initstate_r(unsigned int " seed ", char *" statebuf ,
  39 .BI "                size_t " statelen ", struct random_data *" buf );
  40 .br
  41 .BI "int setstate_r(char *" statebuf ", struct random_data *" buf );
  42 .fi
  43 .sp
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .sp
  49 .ad l
  50 .BR random_r (),
  51 .BR srandom_r (),
  52 .BR initstate_r (),
  53 .BR setstate_r ():
  54 .RS 4
  55 /* Glibc since 2.19: */ _DEFAULT_SOURCE
  56     || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
  57 .RE
  58 .ad b
  59 .SH DESCRIPTION
  60 These functions are the reentrant equivalents
  61 of the functions described in
  62 .BR random (3).
  63 They are suitable for use in multithreaded programs where each thread
  64 needs to obtain an independent, reproducible sequence of random numbers.
  65
  66 The
  67 .BR random_r ()
  68 function is like
  69 .BR random (3),
  70 except that instead of using state information maintained
  71 in a global variable,
  72 it uses the state information in the argument pointed to by
  73 .IR buf ,
  74 which must have been previously initialized by
  75 .BR initstate_r ().
  76 The generated random number is returned in the argument
  77 .IR result .
  78
  79 The
  80 .BR srandom_r ()
  81 function is like
  82 .BR srandom (3),
  83 except that it initializes the seed for the random number generator
  84 whose state is maintained in the object pointed to by
  85 .IR buf ,
  86 which must have been previously initialized by
  87 .BR initstate_r (),
  88 instead of the seed associated with the global state variable.
  89
  90 The
  91 .BR initstate_r ()
  92 function is like
  93 .BR initstate (3)
  94 except that it initializes the state in the object pointed to by
  95 .IR buf ,
  96 rather than initializing the global state variable.
  97
  98 The
  99 .BR setstate_r ()
 100 function is like
 101 .BR setstate (3)
 102 except that it modifies the state in the object pointer to by
 103 .IR buf ,
 104 rather than modifying the global state variable.
 105 .SH RETURN VALUE
 106 All of these functions return 0 on success.
 107 On error, \-1 is returned, with
 108 .I errno
 109 set to indicate the cause of the error.
 110 .SH ERRORS
 111 .TP
 112 .B EINVAL
 113 A state array of less than 8 bytes was specified to
 114 .BR initstate_r ().
 115 .TP
 116 .B EINVAL
 117 The
 118 .I statebuf
 119 or
 120 .I buf
 121 argument to
 122 .BR setstate_r ()
 123 was NULL.
 124 .TP
 125 .B EINVAL
 126 The
 127 .I buf
 128 or
 129 .I result
 130 argument to
 131 .BR random_r ()
 132 was NULL.
 133 .SH ATTRIBUTES
 134 For an explanation of the terms used in this section, see
 135 .BR attributes (7).
 136 .TS
 137 allbox;
 138 lbw27 lb lb
 139 l l l.
 140 Interface       Attribute       Value
 141 T{
 142 .BR random_r (),
 143 .BR srandom_r (),
 144 .br
 145 .BR initstate_r (),
 146 .BR setstate_r ()
 147 T}      Thread safety   MT-Safe race:buf
 148 .TE
 149 .SH CONFORMING TO
 150 These functions are nonstandard glibc extensions.
 151 .\" These functions appear to be on Tru64, but don't seem to be on
 152 .\" Solaris, HP-UX, or FreeBSD.
 153 .SH SEE ALSO
 154 .BR drand48 (3),
 155 .BR rand (3),
 156 .BR random (3)