Passing a structure with shared memory

Question

Hi I want to pass my structure from father to son in C (not c# or c++ ). My problem is to do parsing data in shared memory and out share memory , I must to do this i can't use FIFO or other system

you can assume struct operazione and I use an array of this operazione structure[number]

typedef struct {
    int id;
    char operatore[1];
    int operandoprimo;
    int operandosecondo;
    int risultato;
    int risultato;
    int semid;
} operazione;

sorry some comments are in italian but you can understand easily .

father:

 /* CREO ZONA DI MEMORIA */
   int shmid = cMemC(KEY_MEMORIA,righeoperazioni*(sizeof(operazione)),IPC_CREAT|0666);    
    // 

         // attacco memoria condivisa
          shm =attacMemC(shmid,NULL,0);

          s = shm;

          for(exa=0 ; exa<righeoperazioni ; exa++){

                sprintf(*s++,"%d",comandi[exa].id);
                sprintf(*s++,"%s",comandi[exa].operatore);
                sprintf(*s++,"%d",comandi[exa].operandoprimo);
                sprintf(*s++,"%d",comandi[exa].operandosecondo);
                sprintf(*s++,"%d",comandi[exa].risultato);
                sprintf(*s++,"%d",comandi[exa].semid);
                    }
           s=NULL;

    // 

to son :

operazione comandif[righe];

/* CREO ZONA DI MEMORIA */
    int shmid = cMemC(KEY_MEMORIA,oper*(sizeof(operazione)),IPC_EXCL|0666);   
    // attacco memoria condivisa
    shmf =attacMemC(shmid,NULL,0);
    ss = shmf;
    exa=0;
    for(ss=0 ; ss != NULL ; ss++){
                            sprintf(temp,"%d",*ss);
                comandif[exa].id=atoi(temp);
                sprintf(temp,"%d",*ss);
                sprintf(comandif[exa].operatore,"%s",temp);
                sprintf(temp,"%d",*ss);
                comandif[exa].operandoprimo=atoi(temp);
                sprintf(temp,"%d",*ss);
                comandif[exa].operandosecondo=atoi(temp);
                sprintf(temp,"%d",*ss);
                comandif[exa].risultato=atoi(temp);
                sprintf(temp,"%d",*ss);
                comandif[exa].semid=atoi(temp);
                exa++;
           }

Answer 1

The for loop using sprintf() to 'write' to the shared memory is bogus. What is the type of s ? Its declaration isn't shown, but it doesn't matter much. If it is a char ** , as it should be for its use, you are writing multi-digit numbers into 'single bytes' of memory (it's a bit more complex than that, but it bears no resemblance to copying the structure into shared memory as you should be doing).

You probably need:

operazione *target = (operazione *)shm;
memmove(target, commandi, righeoperazioni * sizeof(operazione));

This will give you copies of the commandi array of operazione structures in your shared memory. You actually don't need the target variable; you could use just:

memmove(shm, commandi, righeoperazione * sizeof(operazione));