/* Copyright (c) 1990 Regents of the University of California. All rights reserved. */ /* FUNCTION <>, <>---pseudo-random numbers INDEX rand INDEX srand INDEX rand_r SYNOPSIS #include int rand(void); void srand(unsigned int <[seed]>); int rand_r(unsigned int *<[seed]>); DESCRIPTION <> 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 <> 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 <>. You can set the random seed using <>; it does nothing beyond storing its argument in the static variable used by <>. 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 <>; or, if you wish to ensure (for example, while debugging) that successive runs of your program use the same ``random'' numbers, you can use <> to set the same random seed at the outset. RETURNS <> returns the next pseudo-random integer in sequence; it is a number between <<0>> and <> (inclusive). <> does not return a result. NOTES <> and <> are unsafe for multi-threaded applications. <> is thread-safe and should be used instead. PORTABILITY <> 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. <> requires no supporting OS subroutines. */ #ifndef _REENT_ONLY #define _DEFAULT_SOURCE #include void srand (unsigned int seed) { srandom(seed); } #endif /* _REENT_ONLY */