Manpage of RAND

RAND

Section: NEWLIB (3)
Updated: 2005 Feb 23
Index Return to Main Contents

NAME

1.29 `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 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.

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.

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.

This document was created by man2html, using the manual pages.
Time: 21:25:29 GMT, May 16, 2005