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)
Hi!
IN THE FOLLOWING PROGRAM THE VALUE OF j REMAINS UNCHANGED . WHY ? IF I WANT A VARIABLE VALUE TO CHANGE LIKE THIS , IS THERE ANY WAY TO DO IT ?
Or do we have to use shared memory variables?
main()
{
int return_pid, i, total;
int j=1;
total = TOTALRECS+1;
for... (2 Replies)
Hi,
I am having trouble with generating random numbers. can this be done with awk?
So I have a file that looks like this:
23 30
24 40
26 34
So column1 is start and column2 is end. I want to generate 3 random #'s between start and stop:
So the output will look like this:
... (9 Replies)
Im new to C, and Im having a hard time getting a random number.
In bash, I would do something similar to the following to get a random number;
#!/bin/bash
seed1=$RANDOM
seed2=$RANDOM
seed3=$RANDOM
SEED=`expr $seed1 * $seed2 / $seed3`
echo ${SEED%.*}
Now, in online examples... (4 Replies)
Hi everyone
i am very new to linux , working on bash shell.
I am trying to solve the given problem
1. Create a process and then create children using fork
2. Check the Status of the application for successful running.
3. Kill all the process(threads) except parent and first child... (2 Replies)
Hi there I am trying to generate a random number between 40 and 70 using the shell here is my code so far and it keeps going above 70. all help much appreciated!
comp=$(( RANDOM%70+40 ))
echo $comp (4 Replies)
Having a hard time with this. Very new to scripting and linux. Spent all sunday trying to do this. Appreciate some help and maybe help breaking down what the syntax does.
Create a Bash program. It should have the following properties
• Creates a secret number between 1 and 100
i. The... (3 Replies)
Hi Guys and gals...
As you know I am getting to grips with POSIX and hit this stumbling block.
Generating two random numbers 0 to 255 POSIXly. Speed in not important hence the 'sleep 1' command.
I have done a demo that works, but it sure is ugly! Is there a better way?
#!/bin/sh
# Random... (12 Replies)
Hi All
Below code is working as expected but creating too many child processes when the url is not up and every minute that process is sending false email alerts
any help with the logic not to generate child process and not to send duplicate alerts
app="https://url"
appresult=$(wget... (2 Replies)
Discussion started by: srilinux09
2 Replies
LEARN ABOUT CENTOS
rand
RAND(3) Linux Programmer's Manual RAND(3)NAME
rand, rand_r, srand - pseudo-random number generator
SYNOPSIS
#include <stdlib.h>
int rand(void);
int rand_r(unsigned int *seedp);
void srand(unsigned int seed);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
rand_r(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
DESCRIPTION
The rand() function returns a pseudo-random integer in the range 0 to RAND_MAX inclusive (i.e., the mathematical range [0, RAND_MAX]).
The srand() function sets its argument as the seed for a new sequence of pseudo-random integers to be returned by rand(). These sequences
are repeatable 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 function rand() is not reentrant or thread-safe, since it uses hidden state that is modified on each call. This might just be the seed
value to be used by the next call, or it might be something more elaborate. In order to get reproducible behavior in a threaded applica-
tion, this state must be made explicit; this can be done using the reentrant function rand_r().
Like rand(), rand_r() returns a pseudo-random integer in the range [0, RAND_MAX]. The seedp argument is a pointer to an unsigned int that
is used to store state between calls. If rand_r() is called with the same initial value for the integer pointed to by seedp, and that
value is not modified between calls, then the same pseudo-random sequence will result.
The value pointed to by the seedp argument of rand_r() provides only a very small amount of state, so this function will be a weak pseudo-
random generator. Try drand48_r(3) instead.
RETURN VALUE
The rand() and rand_r() functions return a value between 0 and RAND_MAX (inclusive). The srand() function returns no value.
CONFORMING TO
The functions rand() and srand() conform to SVr4, 4.3BSD, C89, C99, POSIX.1-2001. The function rand_r() is from POSIX.1-2001.
POSIX.1-2008 marks rand_r() as obsolete.
NOTES
The versions of rand() and srand() in the Linux C Library use the same random number generator as random(3) and srandom(3), so the lower-
order bits should be as random as the higher-order bits. However, on older rand() implementations, and on current implementations on dif-
ferent systems, the lower-order bits are much less random than the higher-order bits. Do not use this function in applications intended to
be portable when good randomness is needed. (Use random(3) instead.)
EXAMPLE
POSIX.1-2001 gives the following example of an implementation of rand() and srand(), possibly useful when one needs the same sequence on
two different machines.
static unsigned long next = 1;
/* RAND_MAX assumed to be 32767 */
int myrand(void) {
next = next * 1103515245 + 12345;
return((unsigned)(next/65536) % 32768);
}
void mysrand(unsigned seed) {
next = seed;
}
The following program can be used to display the pseudo-random sequence produced by rand() when given a particular seed.
#include <stdlib.h>
#include <stdio.h>
int
main(int argc, char *argv[])
{
int j, r, nloops;
unsigned int seed;
if (argc != 3) {
fprintf(stderr, "Usage: %s <seed> <nloops>
", argv[0]);
exit(EXIT_FAILURE);
}
seed = atoi(argv[1]);
nloops = atoi(argv[2]);
srand(seed);
for (j = 0; j < nloops; j++) {
r = rand();
printf("%d
", r);
}
exit(EXIT_SUCCESS);
}
SEE ALSO drand48(3), random(3)COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2010-10-01 RAND(3)