Сегменты памяти

#include <stdio.h>
#include <string.h>
#include <sys/shm.h>
#include <fstream>
#include <iostream>
 
#define SHMEM_SIZE 4096
#define SH_MESSAGE "Hello World!\n"
 
 
int digSum(int n) {
       int sum = 0;
       while(n > 0 || sum > 9) {
            if(n == 0) {
              n = sum;
              sum = 0;
            }
            sum += n % 10;
            n /= 10;
        }
 return sum;
}
 
int main () {
        int shm_id;
        char * shm_buf;
        int shm_size;
        struct shmid_ds ds;
 
        shm_id = shmget (IPC_PRIVATE, SHMEM_SIZE, IPC_CREAT | IPC_EXCL | 0600);
        if (shm_id == -1) {
        std::cerr << "shmget() error" << std::endl;
        return 1;
        }
 
        shm_buf = (char *) shmat (shm_id, NULL, 0);
        if (shm_buf == (char *) -1) {
           std::cerr << "shmat() error" << std::endl;
           return 1;
        }
 
        shmctl (shm_id, IPC_STAT, &ds);
        shm_size = ds.shm_segsz;
        if (shm_size < strlen (SH_MESSAGE)) {
           std::cerr << "Error: segsize= " << shm_size << std::endl;
           return 1;
        }
 
        strcpy (shm_buf, SH_MESSAGE);
        std::cout << "ID: " << shm_id << std::endl;
 
        int n = 1234;
        std::cout << "Number: " << n << std::endl;
        std::cout << "Answer: " << digSum(n) << std::endl;
 
        std::cout << "Press <Enter> to exit";
        fgetc (stdin);
 
        shmdt (shm_buf);
        shmctl (shm_id, IPC_RMID, NULL);
        return 0;
}

#include <sys/shm.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
 
int main(int argc, char** argv) {
        int shm_id;
        char* shm_buf;
 
        if (argc < 2) {
           std::cerr << "Too few arguments" << std::endl;
           return 1;
        }
 
        shm_id = atoi (argv[1]);
        shm_buf = (char*) shmat (shm_id, 0, 0);
 
        if (shm_buf == (char*)-1) {
        std::cerr << "shmat() error" << std::endl;
        return 1;
        }
 
        std::cout << "Message: " <<  shm_buf << std::endl;
        shmdt (shm_buf);
        return 0;
}

        std::cout << "ID: " << shm_id << std::endl;
 
        int n = 1234;
        int sum = digSum(n);
 
        std::cout << "Number: " << n << std::endl;
        std::cout << "Answer: " << sum << std::endl;
 
        sprintf(shm_buf, "%s; answer: %d\n", SH_MESSAGE, sum);
 
        std::cout << "Press <Enter> to exit";
        fgetc (stdin);