initstate(3p) — Linux manual page


INITSTATE(3P)           POSIX Programmer's Manual          INITSTATE(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       initstate, random, setstate, srandom — pseudo-random number

SYNOPSIS         top

       #include <stdlib.h>

       char *initstate(unsigned seed, char *state, size_t size);
       long random(void);
       char *setstate(char *state);
       void srandom(unsigned seed);

DESCRIPTION         top

       The random() function shall use a non-linear additive feedback
       random-number generator employing a default state array size of
       31 long integers to return successive pseudo-random numbers in
       the range from 0 to 231-1. The period of this random-number
       generator is approximately 16 x (231-1). The size of the state
       array determines the period of the random-number generator.
       Increasing the state array size shall increase the period.

       With 256 bytes of state information, the period of the random-
       number generator shall be greater than 269.

       Like rand(), random() shall produce by default a sequence of
       numbers that can be duplicated by calling srandom() with 1 as the

       The srandom() function shall initialize the current state array
       using the value of seed.

       The initstate() and setstate() functions handle restarting and
       changing random-number generators. The initstate() function
       allows a state array, pointed to by the state argument, to be
       initialized for future use. The size argument, which specifies
       the size in bytes of the state array, shall be used by
       initstate() to decide what type of random-number generator to
       use; the larger the state array, the more random the numbers.
       Values for the amount of state information are 8, 32, 64, 128,
       and 256 bytes. Other values greater than 8 bytes are rounded down
       to the nearest one of these values. If initstate() is called with
       8≤size<32, then random() shall use a simple linear congruential
       random number generator. The seed argument specifies a starting
       point for the random-number sequence and provides for restarting
       at the same point. The initstate() function shall return a
       pointer to the previous state information array.

       If initstate() has not been called, then random() shall behave as
       though initstate() had been called with seed=1 and size=128.

       Once a state has been initialized, setstate() allows switching
       between state arrays. The array defined by the state argument
       shall be used for further random-number generation until
       initstate() is called or setstate() is called again. The
       setstate() function shall return a pointer to the previous state

RETURN VALUE         top

       If initstate() is called with size less than 8, it shall return

       The random() function shall return the generated pseudo-random

       The srandom() function shall not return a value.

       Upon successful completion, initstate() and setstate() shall
       return a pointer to the previous state array; otherwise, a null
       pointer shall be returned.

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top



       After initialization, a state array can be restarted at a
       different point in one of two ways:

        1. The initstate() function can be used, with the desired seed,
           state array, and size of the array.

        2. The setstate() function, with the desired state, can be used,
           followed by srandom() with the desired seed. The advantage of
           using both of these functions is that the size of the state
           array does not have to be saved once it is initialized.

       Although some implementations of random() have written messages
       to standard error, such implementations do not conform to

       Issue 5 restored the historical behavior of this function.

       Threaded applications should use erand48(), nrand48(), or
       jrand48() instead of random() when an independent random number
       sequence in multiple threads is required.

       These functions should be avoided whenever non-trivial
       requirements (including safety) have to be fulfilled.

RATIONALE         top




SEE ALSO         top

       drand48(3p), rand(3p)

       The Base Definitions volume of POSIX.1‐2017, stdlib.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see .

IEEE/The Open Group               2017                     INITSTATE(3P)

Pages that refer to this page: stdlib.h(0p)drand48(3p)gethostid(3p)rand(3p)random(3p)setstate(3p)srandom(3p)