Generating Random Number in Child Process using Fork Post: 302597315

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Top Forums Programming Generating Random Number in Child Process using Fork Post 302597315 by manisum on Friday 10th of February 2012 01:45:22 AM

02-10-2012

Registered User

Generating Random Number in Child Process using Fork

Hello All, I am stuck up in a program where the rand functions ends up giving all the same integers. Tried sleep, but the numbers turned out to be same... Can anyone help me out how to fix this issue ? I have called the srand once in the program, but I feel like when I call fork the child process again calls the srand.. any fix for that ?

This is my working code (just the rand function messing up)

Code:

int main (int argc, char *argv[])  
{ 
    
    int seed = time(0);
    sleep(10);
    srand(seed);    
    int i, nproc;
    nproc = atoi(argv[1]);
    pid_t child[nproc];
    
    int status;
    
    if (argc < 2)
    {
        fork(); // if no argument - only one child process is created
    }

    else
    {
        for(i = 0; i < nproc; i++) 
        {
            switch(pid = child[i] = fork())
                {
                    case -1:
                    perror("fork-error");
                    exit(1);

                    case 0:
                    printf("id = %d : RND = %d",i, (int)(rand()% 100 +1)); //generating random number for each child
                    exit(i);

                    default:
                    waitpid(child[i], &status, 0); //wait for the child to terminate
                    printf("Exiting %d = %d\n", i, WEXITSTATUS(status));
                    break;

                }
            
        }
    }    
    return 0; 
}

Last edited by manisum; 02-10-2012 at 02:51 AM..

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LEARN ABOUT SUNOS

rand_r

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 5.10							    19 May 2004 							  rand(3C)

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