1RANDOM_R(3) Linux Programmer's Manual RANDOM_R(3)
2
6 random_r, srandom_r, initstate_r, setstate_r - reentrant random number
7 generator
8
10 #include <stdlib.h>
11 int random_r(struct random_data *restrict buf,
13 int32_t *restrict result);
14 int srandom_r(unsigned int seed, struct random_data *buf);
15 int initstate_r(unsigned int seed, char *restrict statebuf,
17 size_t statelen, struct random_data *restrict buf);
18 int setstate_r(char *restrict statebuf,
19 struct random_data *restrict buf);
20 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
22 random_r(), srandom_r(), initstate_r(), setstate_r():
24 /* Glibc since 2.19: */ _DEFAULT_SOURCE
25 || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
26
28 These functions are the reentrant equivalents of the functions de‐
29 scribed in random(3). They are suitable for use in multithreaded pro‐
30 grams where each thread needs to obtain an independent, reproducible
31 sequence of random numbers.
32 The random_r() function is like random(3), except that instead of using
34 state information maintained in a global variable, it uses the state
35 information in the argument pointed to by buf, which must have been
36 previously initialized by initstate_r(). The generated random number
37 is returned in the argument result.
38 The srandom_r() function is like srandom(3), except that it initializes
40 the seed for the random number generator whose state is maintained in
41 the object pointed to by buf, which must have been previously initial‐
42 ized by initstate_r(), instead of the seed associated with the global
43 state variable.
44 The initstate_r() function is like initstate(3) except that it initial‐
46 izes the state in the object pointed to by buf, rather than initializ‐
47 ing the global state variable. Before calling this function, the
48 buf.state field must be initialized to NULL. The initstate_r() func‐
49 tion records a pointer to the statebuf argument inside the structure
50 pointed to by buf. Thus, statebuf should not be deallocated so long as
51 buf is still in use. (So, statebuf should typically be allocated as a
52 static variable, or allocated on the heap using malloc(3) or similar.)
53 The setstate_r() function is like setstate(3) except that it modifies
55 the state in the object pointed to by buf, rather than modifying the
56 global state variable. state must first have been initialized using
57 initstate_r() or be the result of a previous call of setstate_r().
58
60 All of these functions return 0 on success. On error, -1 is returned,
61 with errno set to indicate the error.
62
64 EINVAL A state array of less than 8 bytes was specified to init‐
65 state_r().
66 EINVAL The statebuf or buf argument to setstate_r() was NULL.
68 EINVAL The buf or result argument to random_r() was NULL.
70
72 For an explanation of the terms used in this section, see at‐
73 tributes(7).
74 ┌───────────────────────────────────┬───────────────┬──────────────────┐
76 │Interface │ Attribute │ Value │
77 ├───────────────────────────────────┼───────────────┼──────────────────┤
78 │random_r(), srandom_r(), │ Thread safety │ MT-Safe race:buf │
79 │initstate_r(), setstate_r() │ │ │
80 └───────────────────────────────────┴───────────────┴──────────────────┘
81
83 These functions are nonstandard glibc extensions.
84
86 The initstate_r() interface is confusing. It appears that the ran‐
87 dom_data type is intended to be opaque, but the implementation requires
88 the user to either initialize the buf.state field to NULL or zero out
89 the entire structure before the call.
90
92 drand48(3), rand(3), random(3)
93
95 This page is part of release 5.13 of the Linux man-pages project. A
96 description of the project, information about reporting bugs, and the
97 latest version of this page, can be found at
98 https://www.kernel.org/doc/man-pages/.
99GNU 2021-03-22 RANDOM_R(3)