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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
RANDOM(3) Linux Programmer's Manual RANDOM(3)
random, srandom, initstate, setstate - random number generator
#include <stdlib.h>
long int random(void);
void srandom(unsigned int seed);
char *initstate(unsigned int seed, char *state, size_t n);
char *setstate(char *state);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
random(), srandom(), initstate(), setstate():
_XOPEN_SOURCE >= 500
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
The random() function uses a nonlinear additive feedback random
number generator employing a default table of size 31 long integers
to return successive pseudo-random numbers in the range from 0 to
RAND_MAX. The period of this random number generator is very large,
approximately 16 * ((2^31) - 1).
The srandom() function sets its argument as the seed for a new
sequence of pseudo-random integers to be returned by random(). These
sequences are repeatable by calling srandom() with the same seed
value. If no seed value is provided, the random() function is
automatically seeded with a value of 1.
The initstate() function allows a state array state to be initialized
for use by random(). The size of the state array n is used by
initstate() to decide how sophisticated a random number generator it
should use—the larger the state array, the better the random numbers
will be. Current "optimal" values for the size of the state array n
are 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down
to the nearest known amount. Using less than 8 bytes results in an
error. seed is the seed for the initialization, which specifies a
starting point for the random number sequence, and provides for
restarting at the same point.
The setstate() function changes the state array used by the random()
function. The state array state is used for random number generation
until the next call to initstate() or setstate(). state must first
have been initialized using initstate() or be the result of a
previous call of setstate().
The random() function returns a value between 0 and RAND_MAX. The
srandom() function returns no value.
The initstate() function returns a pointer to the previous state
array. On error, errno is set to indicate the cause.
On success, setstate() returns a pointer to the previous state array.
On error, it returns NULL, with errno set to indicate the cause of
the error.
EINVAL The state argument given to setstate() was NULL.
EINVAL A state array of less than 8 bytes was specified to
initstate().
For an explanation of the terms used in this section, see
attributes(7).
┌────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────┼───────────────┼─────────┤
│random(), srandom(), │ Thread safety │ MT-Safe │
│initstate(), setstate() │ │ │
└────────────────────────┴───────────────┴─────────┘
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
The random() function should not be used in multithreaded programs
where reproducible behavior is required. Use random_r(3) for that
purpose.
Random-number generation is a complex topic. Numerical Recipes in C:
The Art of Scientific Computing (William H. Press, Brian P. Flannery,
Saul A. Teukolsky, William T. Vetterling; New York: Cambridge
University Press, 2007, 3rd ed.) provides an excellent discussion of
practical random-number generation issues in Chapter 7 (Random
Numbers).
For a more theoretical discussion which also covers many practical
issues in depth, see Chapter 3 (Random Numbers) in Donald E. Knuth's
The Art of Computer Programming, volume 2 (Seminumerical Algorithms),
2nd ed.; Reading, Massachusetts: Addison-Wesley Publishing Company,
1981.
According to POSIX, initstate() should return NULL on error. In the
glibc implementation, errno is (as specified) set on error, but the
function does not return NULL.
getrandom(2), drand48(3), rand(3), random_r(3), srand(3)
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GNU 2017-03-13 RANDOM(3)
Pages that refer to this page: drand48(3), drand48_r(3), rand(3), random_r(3)