random(3) - Linux manual page (original) (raw)
random(3) Library Functions Manual random(3)
NAME top
random, srandom, initstate, setstate - random number generatorLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <stdlib.h>**
**long random(void);**
**void srandom(unsigned int** _seed_**);**
**char *initstate(unsigned int** _seed_**, char** _state_**[.**_n_**], 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 >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCEDESCRIPTION top
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 2^31 - 1. 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**().RETURN VALUE top
The **random**() function returns a value between 0 and _(2^31) - 1_.
The **srandom**() function returns no value.
The **initstate**() function returns a pointer to the previous state
array. On failure, it returns NULL, and _[errno](../man3/errno.3.html)_ is set to indicate
the error.
On success, **setstate**() returns a pointer to the previous state
array. On failure, it returns NULL, and _[errno](../man3/errno.3.html)_ is set to indicate
the error.ERRORS top
**EINVAL** The _state_ argument given to **setstate**() was NULL.
**EINVAL** A state array of less than 8 bytes was specified to
**initstate**().ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────────┼───────────────┼─────────┤
│ **random**(), **srandom**(), **initstate**(), │ Thread safety │ MT-Safe │
│ **setstate**() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘STANDARDS top
POSIX.1-2008.HISTORY top
POSIX.1-2001, 4.3BSD.NOTES top
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.CAVEATS top
The **random**() function should not be used in multithreaded programs
where reproducible behavior is required. Use [random_r(3)](../man3/random%5Fr.3.html) for that
purpose.BUGS top
According to POSIX, **initstate**() should return NULL on error. In
the glibc implementation, _[errno](../man3/errno.3.html)_ is (as specified) set on error,
but the function does not return NULL.SEE ALSO top
[getrandom(2)](../man2/getrandom.2.html), [drand48(3)](../man3/drand48.3.html), [rand(3)](../man3/rand.3.html), [random_r(3)](../man3/random%5Fr.3.html), [srand(3)](../man3/srand.3.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 random(3)
Pages that refer to this page:drand48(3), drand48_r(3), rand(3), random_r(3)