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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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INITSTATE(3P) POSIX Programmer's Manual INITSTATE(3P)
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.
initstate, random, setstate, srandom — pseudo-random number
functions
#include <stdlib.h>
char *initstate(unsigned seed, char *state, size_t size);
long random(void);
char *setstate(char *state);
void srandom(unsigned seed);
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
seed.
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
array.
If initstate() is called with size less than 8, it shall return
NULL.
The random() function shall return the generated pseudo-random
number.
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.
No errors are defined.
The following sections are informative.
None.
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
POSIX.1‐2008.
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.
None.
None.
drand48(3p), rand(3p)
The Base Definitions volume of POSIX.1‐2017, stdlib.h(0p)
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
http://www.opengroup.org/unix/online.html .
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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
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)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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