rand,
srand
[pseudo-random numbers]
SYNOPSIS
#include
<stdlib.h>
int rand(void);
void srand(unsigned
int seed);
int _rand_r(void
*reent);
void _srand_r(void
*reent, unsigned
int seed);
DESCRIPTION
rand
returns a different integer each time
it is called; each integer is chosen by an algorithm designed to be unpredictable,
so that you can use rand
when you require a random number. The
algorithm depends on a static variable called the random seed; starting
with a given value of the random seed always produces the same sequence
of numbers in successive calls to rand.
You can set the random seed using srand; it does nothing beyond storing its argument in the static variable used by rand. You can exploit this to make the pseudo-random sequence less predictable, if you wish, by using some other unpredictable value (often the least significant parts of a time-varying value) as the random seed before beginning a sequence of calls to rand; or, if you wish to ensure (for example, while debugging) that successive runs of your program use the same random numbers, you can use srand to set the same random seed at the outset.
_rand_r and _srand_r are reentrant versions of rand and srand. The extra argument, reent, is a pointer to a reentrancy structure.
RETURNS
rand
returns the next pseudo-random integer
in sequence; it is a number between 0
and RAND_MAX
(inclusive).
srand does not return a result.
COMPLIANCE
rand
is required by ANSI, but the algorithm
for pseudo-random number generation is not specified; therefore, even if
you use the same random seed, you cannot expect the same sequence of results
on two different systems.
rand requires no supporting OS subroutines.
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