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#include <stdio.h>
#include<sys/types.h>
#include<unistd.h>
#include<stdlib.h>
#include<string.h>
#include<fcntl.h>
#include<sys/shm.h>
#include<sys/stat.h>
 
int main() {
	// your code goes here
	const int nSize = 4096;
	const char *pName = "OS";
	int shm_fd;
	void *ptr = NULL;
 
	printf("Please input a positive number\n");
	int n;
	scanf("%d",&n);
	if(n <= 0)
	{
		printf("Input positive number\n");
		return 1;
	}
 
 
	pid_t pid;
	pid = fork();
	if(pid < 0)
	{
		printf("fork error\n");
		return 1;
	}
	else if(pid == 0)
	{
		shm_fd = shm_open(pName,O_CREAT|O_RDRW,0666);
		ftruncate(shm_fd,nSize);
		ptr = mmap(0,nSize,PROT_WRITE,MAP_SHARED,shm_fd,0);
 
		char buf[10];
		sprintf(buf,"%d ",n);
		sprintf(ptr,"%s",buf);
		ptr += strlen(buf);
		while(n > 1)
		{
			if(n%2 == 0)
			{
				n /=2;
				sprintf(buf,"%d ",n);
				sprintf(ptr,"%s",buf);
				ptr += strlen(buf);
			}
			else
			{	
				n =3*n + 1;
				sprintf(buf,"%d ",n);
				sprintf(ptr,"%s",buf);
				ptr += strlen(buf);
			}
		}
	}
	else
	{
		//sleep(10);
		int st;
		wait(&st);
		shm_fd = shm_open(pName,O_RDONLY,0666);
		ptr = mmap(0,nSize,PROT_READ,MAP_SHARED,shm_fd,0);
		printf("Child[%d] Complete[%d]\n",pid,st);
		printf("%s\n",(char *)ptr);
		shm_unlink(pName);
	}
	return 0;
}
 

prog.c: In function ‘main’:
prog.c:36:12: warning: implicit declaration of function ‘shm_open’; did you mean ‘shmget’? [-Wimplicit-function-declaration]
   shm_fd = shm_open(pName,O_CREAT|O_RDRW,0666);
            ^~~~~~~~
            shmget
prog.c:36:35: error: ‘O_RDRW’ undeclared (first use in this function); did you mean ‘O_RDWR’?
   shm_fd = shm_open(pName,O_CREAT|O_RDRW,0666);
                                   ^~~~~~
                                   O_RDWR
prog.c:36:35: note: each undeclared identifier is reported only once for each function it appears in
prog.c:38:9: warning: implicit declaration of function ‘mmap’ [-Wimplicit-function-declaration]
   ptr = mmap(0,nSize,PROT_WRITE,MAP_SHARED,shm_fd,0);
         ^~~~
prog.c:38:22: error: ‘PROT_WRITE’ undeclared (first use in this function)
   ptr = mmap(0,nSize,PROT_WRITE,MAP_SHARED,shm_fd,0);
                      ^~~~~~~~~~
prog.c:38:33: error: ‘MAP_SHARED’ undeclared (first use in this function)
   ptr = mmap(0,nSize,PROT_WRITE,MAP_SHARED,shm_fd,0);
                                 ^~~~~~~~~~
prog.c:66:3: warning: implicit declaration of function ‘wait’; did you mean ‘main’? [-Wimplicit-function-declaration]
   wait(&st);
   ^~~~
   main
prog.c:68:22: error: ‘PROT_READ’ undeclared (first use in this function)
   ptr = mmap(0,nSize,PROT_READ,MAP_SHARED,shm_fd,0);
                      ^~~~~~~~~
prog.c:71:3: warning: implicit declaration of function ‘shm_unlink’; did you mean ‘unlink’? [-Wimplicit-function-declaration]
   shm_unlink(pName);
   ^~~~~~~~~~
   unlink
prog.c:19:2: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
  ^~~~~~~~~~~~~~
prog.c:37:3: warning: ignoring return value of ‘ftruncate’, declared with attribute warn_unused_result [-Wunused-result]
   ftruncate(shm_fd,nSize);
   ^~~~~~~~~~~~~~~~~~~~~~~

Standard output is empty