Programming

struct sharedInfo {
     string szName;
     int iAge;
     string szAddrees;
};

extern "C" {
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
}

#include <iostream>
#include <vector>

using namespace std;


typedef struct sample{
        int iCount;
        string szName;
}sample;

int CreateSharedMem(key_t key) {
        int shmid=-1;
        if ((shmid = shmget(key,sizeof(sample),IPC_CREAT|0666)) < 0) {
                cout << "Unable to get value " << endl;
                perror("shmget");
                return -1;
        }
        return shmid;
}

int main() {
        pid_t pid;
        int shmid;
        key_t key;
        key = 1001;
        /* create shared memory */
        shmid = CreateSharedMem(key);

        sample *ostData;

        /* attach shared memory */
        if ( (ostData = (sample *) shmat(shmid,NULL,0)) == NULL) {
                cout << " Unable to attach to Shared region." << endl;
                exit(1);
        }

        sample *smp = new (ostData) sample();
        smp->szName = "abcxyz";
        /* doing above b'coz can't assign directly to szName */

        ostData->iCount = 0;

        if ( (pid = fork())< 0 ) {
                perror("pid");
                exit(1);
        }else if(pid == 0) { // child
                if((shmid = shmget(key,sizeof(sample),0666)) < 0) {
                        cout << "Faild to create shared segment." << endl;
                        exit(1);
                }
                sample *ostData =(sample *) shmat(shmid,NULL,0);
                cout << "---------------- child ------------------- " << endl;
                cout << "ostData->szName : " << ostData->szName <<endl;
                cout << "ostData->iCount : " << ostData->iCount <<endl;
                /* changing in child */
                ostData->szName = "xyzabc";
                ostData->iCount = 10;

                shmdt(ostData);
        }else { // parent
                int status;
                waitpid(pid,&status,WNOHANG);
                cout << "-------------- Parent ------------------- " << endl;
                cout << "ostData->szName : " << ostData->szName <<endl;
                cout << "ostData->iCount : " << ostData->iCount << endl;
                /* in parent the change of count is reflected but name doesn't */
        }
        ostData->~sample();
        shmdt(ostData);
        shmctl(shmid,IPC_RMID,NULL);
        return 0;
}