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rand(3c)
Standard C Library Functions rand(3C)
NAME
rand, srand, rand_r - simple random-number generator
SYNOPSIS
#include <stdlib.h>
int rand(void);
void srand(unsigned int seed);
int rand_r(unsigned int *seed);
DESCRIPTION
The rand() function uses a multiplicative congruential random-number
generator with period 2^32 that returns successive pseudo-random num‐
bers in the range of 0 to RAND_MAX (defined in <stdlib.h>).
The srand() function uses the argument seed as a seed for a new
sequence of pseudo-random numbers to be returned by subsequent calls to
rand(). If srand() is then called with the same seed value, the
sequence of pseudo-random numbers will be repeated. If rand() is called
before any calls to srand() have been made, the same sequence will be
generated as when srand() is first called with a seed value of 1.
The rand_r() function has the same functionality as rand() except that
a pointer to a seed seed must be supplied by the caller. If rand_r() is
called with the same initial value for the object pointed to by seed
and that object is not modified between successive calls to rand_r(),
the same sequence as that produced by calls to rand() will be gener‐
ated.
The rand() and srand() functions provide per-process pseudo-random
streams shared by all threads. The same effect can be achieved if all
threads call rand_r() with a pointer to the same seed object. The
rand_r() function allows a thread to generate a private pseudo-random
stream by having the seed object be private to the thread.
USAGE
The spectral properties of rand() are limited. The drand48(3C) function
provides a better, more elaborate random-number generator.
Programmers should use /dev/urandom or /dev/random for most random-num‐
ber generation, especially for cryptographic purposes. See random(4D).
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelSafe _ Standard‐
See standards(7).
SEE ALSO
drand48(3C), random(4D), attributes(7), standards(7)
Oracle Solaris 11.4 16 May 2014 rand(3C)