opensolaris man page for rand

rand(3C)						   Standard C Library Functions 						  rand(3C)

NAME
       rand, srand, rand_r - simple random-number generator

SYNOPSIS
       #include <stdlib.h>

       int rand(void);

       void srand(unsigned int seed);

       int rand_r(unsigned int *seed);

DESCRIPTION
       The  rand() function uses a multiplicative congruential random-number generator with period 2^32 that returns successive pseudo-random num-
       bers in the range of 0 to RAND_MAX (defined in <stdlib.h>).

       The  srand() function uses the argument seed as a seed for a new sequence of pseudo-random numbers to be returned by  subsequent  calls	to
       rand().	If  srand()  is then called with the same seed value, the sequence of pseudo-random numbers will be repeated.  If rand() is called
       before any calls to srand() have been made, the same sequence will be generated as when srand() is first called with a seed value of 1.

       The rand_r() function has the same functionality as rand() except that a pointer to a seed   seed  must	be  supplied  by  the  caller.	If
       rand_r()  is  called with the same initial value for the object pointed to by seed and that object is not modified between successive calls
       to rand_r(), the same sequence as that produced by calls to rand() will be generated.

       The rand() and srand() functions provide per-process pseudo-random streams shared by all threads. The same effect can be  achieved  if  all
       threads	call  rand_r()	with  a pointer to the same seed object. The rand_r() function allows a thread to generate a private pseudo-random
       stream by having the seed object be private to the thread.

USAGE
       The spectral properties of rand() are limited.  The drand48(3C) function provides a better, more elaborate random-number generator.

       When compiling multithreaded applications, the  _REENTRANT flag must be defined on the compile line.  This flag should be used only in mul-
       tithreaded applications.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO
       drand48(3C), attributes(5), standards(5)

SunOS 5.11							    19 May 2004 							  rand(3C)