problems at a half-duplix shared-memory based chat app

[ENG H]

Hi there ...
I'm trying to build two process that uses Shared memory to exchange messages...
what I'm doing as you will see , is requesting for a shared memory and then putting a struct in it .
the struct consist of a string , Bool flag and an enum values ..
the string should hold the message , the flag should tell whether this message has been seen or not by the other side (cause no one is allowed to add a message if there is a unread message in the memory )
I'm suffering from several problems
1- i cant reach the string at the string....
2- when i replaced the string with an int , i face a problem at the client side when trying to get to the memory
and this is the code ...




Server's side

#include <iostream>
#include <sys/types.h>
#include <sys/ipc.h>
#include <string.h>
#include <sys/shm.h>
using namespace std;
enum e {Server,Client}; //enumeration that will be used to determine who wrote the message
struct chat             // struct that will reside in the memory
{
   string  letter;      //the message it self

    bool ifread;        //boolian variable to determine if the message has been raed or not
    e who;
    int x;
    };


int main(void)
{
   string name;

    cout << "Welcome to the chat room application....please enter your Alias" << endl;
    cin>>name; //taking the name that will be used in the chat

   int shmid; //the id of the shard memory area
   key_t key=ftok(".",'g');//generating a key for the shared memory
   shmid=shmget(key,sizeof(chat),IPC_CREAT | 0666); //creating the shared memory
    if (shmid<0)
    {cout<<"an Error has happend please try again"<<endl;
    return(1);
    }
    chat *str ;         // pointer to the struct
    str=(chat*)shmat(shmid,NULL,0);// attaching the shared memory area to the struct's pointer...
    int temp;           //temp area to store the read input
    /*while(temp!=5)    //keep waiting for the right input to quit
    {
        cout<<"please enter the num"<<endl;
        cin>>temp;

        if(str->ifread)
        {str->ifread=false;
        str->x=temp;
        str->who=Server;
        }
        else if(!str->ifread && str->who==Client)
        {
            cout<<str->x<<endl;

            }
        else{sleep(1);}

  }
*/
while(str->x!=5)
{
    str->ifread=false;
    cout<<"Enter #"<<endl;
    cin>>str->x;

while(str->ifread==false)
{
cout<<"waiting"<<endl;
sleep(1);
}

cout<<str->x<<endl;
}

shmctl (shmid, IPC_RMID, NULL);

}

Client's Side

#include <iostream>
#include <sys/types.h>
#include <sys/ipc.h>
#include <string.h>
#include <sys/shm.h>
using namespace std;
enum e {Server,Client}; //enumeration that will be used to determine who wrote the message
struct chat             // struct that will reside in the memory
{
   string  letter;      //the message it self

    bool ifread;        //boolian variable to determin if the message has been raed or not
    e who;
    int x;
    };


int main(void)
{
   string name;

    cout << "Welcome to the chat room application....please enter your Aliase" << endl;
    cin>>name; //taking the name that will be used in the chat

   int shmid; //the id of the shard memory area
   key_t key=ftok(".",'g');//generating a key for the shared memory
  
   shmid=shmget(key,sizeof(chat),0666); //requesting the shared memory
    if (shmid<0)
    {cout<<"an Error has happened please try again"<<endl;
    return(1);
    }
    chat *str ;         // pointer to the struct
    str=(chat*)shmat(shmid,NULL,0);// attaching the shared memory area to the struct's pointer...
    int temp;           //temp area to store the read input
   /* while(temp!=5)    //keep waiting for the right input to quit
    {
        cout<<"please enter the num"<<endl;
        cin>>temp;
        
        if(str->ifread)
        {str->ifread=false;
        str->x=temp;
        str->who=Client;
        }
        else if(!str->ifread && str->who==Server)
        {
            cout<<str->x;

            }
        else{sleep(1);}

    }

*/
while(str->x!=5)
{
str->ifread=false;
cout<<"please #"<<endl;
cin>>str->x;
while(str->ifread==false)
{sleep(1);
cout<<"waiting"<<endl;
}
cout<<str->x<<endl;


}
shmctl (shmid, IPC_RMID, NULL);
}

Thanks in advance , and sorry for the bad English .....

[kbw]

You can't do that. If you're going to use shared memory, you can only put POD (plain old data) types in it; you know, int, long, double, char ... and arrays of those types.

Why? Because objects (like string) allocate memory and use pointers to that memory. A pointer is only meaningful within a process.