1 .\" Copyright 2008 Michael Kerrisk <mtk.manpages@gmail.com>
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
6 .\" preserved on all copies.
8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
26 .TH RANDOM_R 3 2021-03-22 "GNU" "Linux Programmer's Manual"
28 random_r, srandom_r, initstate_r, setstate_r \- reentrant
29 random number generator
32 .B #include <stdlib.h>
34 .BI "int random_r(struct random_data *restrict " buf ,
35 .BI " int32_t *restrict " result );
36 .BI "int srandom_r(unsigned int " seed ", struct random_data *" buf );
38 .BI "int initstate_r(unsigned int " seed ", char *restrict " statebuf ,
39 .BI " size_t " statelen ", struct random_data *restrict " buf );
40 .BI "int setstate_r(char *restrict " statebuf ,
41 .BI " struct random_data *restrict " buf );
45 Feature Test Macro Requirements for glibc (see
46 .BR feature_test_macros (7)):
54 /* Glibc since 2.19: */ _DEFAULT_SOURCE
55 || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
58 These functions are the reentrant equivalents
59 of the functions described in
61 They are suitable for use in multithreaded programs where each thread
62 needs to obtain an independent, reproducible sequence of random numbers.
68 except that instead of using state information maintained
70 it uses the state information in the argument pointed to by
72 which must have been previously initialized by
74 The generated random number is returned in the argument
81 except that it initializes the seed for the random number generator
82 whose state is maintained in the object pointed to by
84 which must have been previously initialized by
86 instead of the seed associated with the global state variable.
92 except that it initializes the state in the object pointed to by
94 rather than initializing the global state variable.
95 Before calling this function, the
97 field must be initialized to NULL.
100 function records a pointer to the
102 argument inside the structure pointed to by
106 should not be deallocated so long as
111 should typically be allocated as a static variable,
112 or allocated on the heap using
120 except that it modifies the state in the object pointed to by
122 rather than modifying the global state variable.
123 \fIstate\fP must first have been initialized
126 or be the result of a previous call of
129 All of these functions return 0 on success.
130 On error, \-1 is returned, with
132 set to indicate the error.
136 A state array of less than 8 bytes was specified to
157 For an explanation of the terms used in this section, see
165 Interface Attribute Value
171 T} Thread safety MT-Safe race:buf
177 These functions are nonstandard glibc extensions.
178 .\" These functions appear to be on Tru64, but don't seem to be on
179 .\" Solaris, HP-UX, or FreeBSD.
183 interface is confusing.
184 .\" FIXME . https://sourceware.org/bugzilla/show_bug.cgi?id=3662
187 type is intended to be opaque,
188 but the implementation requires the user to either initialize the
190 field to NULL or zero out the entire structure before the call.