Manual Pages for UNIX Operating System command usage for man srand

Standard C Library Functions                             rand(3C)



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

SYNOPSIS
     #include 

     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 suc-
     cessive pseudo-random numbers in the range of 0 to  RAND_MAX
     (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 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 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 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.




SunOS 5.11          Last change: 19 May 2004                    1






Standard C Library Functions                             rand(3C)



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

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



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | MT-Level                    | Safe                        |
    |_____________________________|_____________________________|
    | Standard                    | See standards(5).           |
    |_____________________________|_____________________________|


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
































SunOS 5.11          Last change: 19 May 2004                    2