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

       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

       │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

       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

       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,

       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)

       This page is part of release 5.02 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

GNU                               2019-03-06                         RANDOM(3)