Standard C Library Functions                             rand(3C)



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

SYNOPSIS
     #include 

     int rand(void);


     void srand(unsigned int seed);


     int randr(unsigned int *seed);


DESCRIPTION
     The  rand()  function  uses  a  multiplicative  congruential
     random-number  generator  with period 2^32 that returns suc-
     cessive pseudo-random numbers in the range of 0 to  RANDMAX
     (defined in ).


     The  srand() function uses the argument seed as a seed for a
     new sequence of pseudo-random numbers to be returned by sub-
     sequent 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 randr() function has the same functionality  as  rand()
     except  that  a  pointer to a seed  seed must be supplied by
     the caller. If randr() is  called  with  the  same  initial
     value  for  the object pointed to by seed and that object is
     not modified between successive calls to randr(), the  same
     sequence  as  that  produced by calls to rand() will be gen-
     erated.


     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 randr() with a  pointer
     to  the  same  seed  object.  The randr() 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.




SunOS 5.11          Last change: 19 May 2004                    1






Standard C Library Functions                             rand(3C)



     When compiling multithreaded applications,  the   RENTRANT
     flag  must be defined on the compile line.  This flag should
     be used only in multithreaded applications.

ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     
           ATRIBUTE TYPE               ATRIBUTE VALUE       
    
     Interface Stability          Standard                    
    
     MT-Level                     Safe                        
    


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


































SunOS 5.11          Last change: 19 May 2004                    2