How can i user string or vector ins shared memory ?

For example i have a structure sharedInfo like below

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

Hi,

Fire your favorite web browser, and give in your favorite search engine "stl container shared memory". You should be lucky.

The fastest way is probably to reuse the wheel others have already invented:
Chapter 9. Boost.Interprocess

Cheers,
Loïc

Yes, it will crash because "string" (if this is C) would be a char * allocated on the heap, and if this is c++, is probably the same (but I suppose the C++ STL could implement it any way they wanted). Regardless, it's not going to be compatible with shared memory.

So...as Loic said, you'll have to either live with a predefined size for the entire shared memory segment, or use a separated shared memory management library. It seems even the shared memory management library he supplies, however, is unfortunately not going to be directly compatible with string. Or at least at first blush, it didn't appear to be. It just allows you to dynamically allocate from a shared memory segment (which still must have a fixed size).

Is there any other alternative to use STL in Shared memory ? What about memory mapped files ?

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;
}