1RANDOM(3) Linux Programmer's Manual RANDOM(3)
2
6 random, srandom, initstate, setstate - random number generator
7
9 #include <stdlib.h>
10 long int random(void);
12 void srandom(unsigned int seed);
14 char *initstate(unsigned int seed, char *state, size_t n);
16 char *setstate(char *state);
17 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
19 random(), srandom(), initstate(), setstate(): _SVID_SOURCE ||
21 _BSD_SOURCE || _XOPEN_SOURCE >= 500
22
24 The random() function uses a non-linear additive feedback random number
25 generator employing a default table of size 31 long integers to return
26 successive pseudo-random numbers in the range from 0 to RAND_MAX. The
27 period of this random number generator is very large, approximately
28 16 * ((2^31) - 1).
29 The srandom() function sets its argument as the seed for a new sequence
31 of pseudo-random integers to be returned by random(). These sequences
32 are repeatable by calling srandom() with the same seed value. If no
33 seed value is provided, the random() function is automatically seeded
34 with a value of 1.
35 The initstate() function allows a state array state to be initialized
37 for use by random(). The size of the state array n is used by init‐
38 state() to decide how sophisticated a random number generator it should
39 use — the larger the state array, the better the random numbers will
40 be. seed is the seed for the initialization, which specifies a start‐
41 ing point for the random number sequence, and provides for restarting
42 at the same point.
43 The setstate() function changes the state array used by the random()
45 function. The state array state is used for random number generation
46 until the next call to initstate() or setstate(). state must first
47 have been initialized using initstate() or be the result of a previous
48 call of setstate().
49
51 The random() function returns a value between 0 and RAND_MAX. The
52 srandom() function returns no value. The initstate() and setstate()
53 functions return a pointer to the previous state array, or NULL on
54 error.
55
57 EINVAL A state array of less than 8 bytes was specified to initstate().
58
60 4.3BSD, POSIX.1-2001.
61
63 Current "optimal" values for the size of the state array n are 8, 32,
64 64, 128, and 256 bytes; other amounts will be rounded down to the near‐
65 est known amount. Using less than 8 bytes will cause an error.
66 This function should not be used in cases where multiple threads use
68 random() and the behavior should be reproducible. Use random_r(3) for
69 that purpose.
70 Random-number generation is a complex topic. Numerical Recipes in C:
72 The Art of Scientific Computing (William H. Press, Brian P. Flannery,
73 Saul A. Teukolsky, William T. Vetterling; New York: Cambridge Univer‐
74 sity Press, 2007, 3rd ed.) provides an excellent discussion of practi‐
75 cal random-number generation issues in Chapter 7 (Random Numbers).
76 For a more theoretical discussion which also covers many practical
78 issues in depth, see Chapter 3 (Random Numbers) in Donald E. Knuth's
79 The Art of Computer Programming, volume 2 (Seminumerical Algorithms),
80 2nd ed.; Reading, Massachusetts: Addison-Wesley Publishing Company,
81 1981.
82
84 drand48(3), rand(3), random_r(3), srand(3)
85
87 This page is part of release 3.22 of the Linux man-pages project. A
88 description of the project, and information about reporting bugs, can
89 be found at http://www.kernel.org/doc/man-pages/.
90GNU 2009-02-03 RANDOM(3)