RAND(3) NEWLIB RAND(3)NAME
2.32 `rand', `srand'--pseudo-random numbers
SYNOPSIS
#include <stdlib.h>
int rand(void);
void srand(unsigned int SEED);
int rand_r(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 suc‐
cessive 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 sig‐
nificant 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.
RETURNS
`rand' returns the next pseudo-random integer in sequence; it is a num‐
ber between `0' and `RAND_MAX' (inclusive).
`srand' does not return a result.
PORTABILITY
`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.
SEE ALSOrand is part of the library. The full documentation for is maintained
as a Texinfo manual. If info and are properly installed at your site,
the command
info
will give you access to the complete manual.
NEWLIB April 2010 RAND(3)
