RAND(3) BSD Programmer's Manual RAND(3)[top]NAMErand, rand_r,srand- bad random number generatorSYNOPSIS#include <stdlib.h> void srand(unsigned seed); int rand(void); int rand_r(unsigned int *seed);DESCRIPTIONThese interfaces are obsoleted by random(3). The rand() function computes a sequence of pseudo-random integers in the range of 0 to RAND_MAX (as defined by the header file <stdlib.h>). The srand() function sets its argument as the seed for a new sequence of pseudo-random numbers to be returned by rand(). These sequences are re- peatable by calling srand() with the same seed value. If no seed value is provided, the rand() function is automatically seeded with a value of 1. The rand_r() function computes a sequence of pseudo-random integers as in rand() but the value pointed to by seed is used to seed the random-number calculation. Calling rand(),and srand() within a multi-threaded application is sup- ported and provides a single process-specific random number sequence that is shared by the calling threads. The rand_r() function may be used to provide a per-thread random number sequence. The generator is a linear congruential type as described in Knuth, The Art of Computer Programming: Vol. 2, Seminumerical Algorithms, 1981. Each successive term is determined by the formula: x = x * 1103515245 + 12345 The modulus is achieved by using C's rules for unsigned arithmetic, and is therefore a power of two. By the mathematics governing such genera- tors, reducing this generator by a multiple of any smaller power of two also reduces the corresponding sequence period. For instance, the low bit of each successive term is alternately 0 and 1, regardless of the seed. In this sense, the upper bits of each number are ``more random'' than the lower bits. Thus, although the RAND_MAX constant is 32768, the rand() and rand_r() functions discard the lowest 16 bits of each term and return the next 15 bits. Users should discard additional low-order bits from the return value first, or better yet, use one of the alternative generators such as lrand48(3) or random(3).SEE ALSOlrand48(3), random(3)STANDARDSThe rand() and srand() functions conform to ANSI C X3.159-1989 (``ANSI C ''). The rand_r() function conforms to IEEE Std1003.1c (``POSIX'').BSDI BSD/OS June 4, 1993 1

List of man pages available for

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]

Polar

Member of Polar

Based on Fawad Halim's script.

....................................................................

Vote for polarhome |