Shared memory with forked child - c

Question

I have the following code which is supposed to create a forked process to execute the Collatz conjecture (based on a passed value), and push the integers into shared memory. When the child process is done, the parent process is supposed to print out the values. For some reason, my code works sometimes but not others. From debug statements, I can see the values get pushed in but sometimes the code to print out the values doesn't appear to execute (just some blank lines get printed). I am using Debian Linux in a virtual box.
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/shm.h>
#include <sys/mman.h>
int main()
{
const int SIZE = 2048;
const char *name = "SHARON";
int shm_fd;
void *ptr;
int count = 1;
/* Setup shared memory */
shm_fd = shm_open(name, O_CREAT | O_RDWR, 0666);
ftruncate(shm_fd, SIZE);
ptr = mmap(0, SIZE, PROT_WRITE, MAP_SHARED, shm_fd, 0);
/* Get the starting value */
int value;
printf("Enter a positive integer value: ");
scanf("%d", &value);
printf("\n");
if (value < 0)
{
printf("ERROR: Integer value must be positive!");
return 1;
}
/* Fork child process */
pid_t pid;
pid = fork();
fork();
if (pid < 0)
{
fprintf(stderr, "FORK FAILED\n");
return 1;
}
else if (pid > 0) /*parent process*/
{
wait(); /*wait for child to send */
while (atoi((char *)ptr) != 0) /*0 is terminate value*/
{
printf("%s", (char *)ptr);
ptr += sizeof(int);
if (atoi((char *)ptr) != 0)
printf(", ");
}
printf("\n");
shm_unlink(name);
}
else if (pid == 0) /* child process */
{
sprintf(ptr, "%d", value);
ptr += sizeof(value);
while (value != 1)
{
if (value % 2 == 0)
value /= 2;
else
value = value * 3 + 1;
sprintf(ptr, "%d", value);
ptr += sizeof(value);
}
sprintf(ptr,"0"); //push a "terminate" value
ptr += sizeof(value);
}
return 0;
}
Any hints on what I'm doing wrong?

Answer 1

There is two fork() call. which will create two child.
pid = fork();
//fork();
Can you try with above.