Thread: column duplicated in IPC shared memory

Hello, i have tried everything i can imagine but i cant figure out whats going wrong here.

in the player struct , there is a 6x6 matrix, which i fill in the create_player function but when i print it i got 7 columns? then i try to place a '0' in the matrix with the place_ship function, but when the column is 5 it add 2 ceros?

if i reduce the j iterations then i got duplicated in the column 4? or 3 or 2...

is this really a duplicated column? or am i doing something wrong in the code? i searched and tried different things the hole day but cant get it

hope anyone can help me,
Thanks in advice!!

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <pthread.h>
#include <signal.h>     


#define SHMEM_SIZE 1024
#define SHM_KEY 1210
#define SHM_V_KEY 1012


typedef struct{
      char board[6][6]; 
      int thread_ret;
      pthread_t thread;
}player;


player *shm;
int *shm_v;


void *shoot(void *target){
      printf("under construction\n");
}


//shm[shm_v[1]]->thread_ret = pthread_create(&shm[shm_v[1]]->thread, NULL, shoot, );


void fill_matrix(){
      for (size_t i = 0; i < 6; i++) {
            for (size_t j = 0; j < 6; j++) {
                  shm[shm_v[1]].board[i][j] = '*';
            }
      }
}


void place_ship(){
      int x, y;      srand(time(NULL));
      x = rand() & 5;
      y = rand() & 5;
      printf("x = %d\ny = %d\n", x,y);
      shm[shm_v[1]]->board[3][5] = '0';
}


void print_player(player *p){
      for (size_t i = 0; i < 6; i++) {
            for (size_t j = 0; j < 6; j++) {
                  printf("|%c", shm[shm_v[1]].board[i][j]);
                  if (j == 5) {
                        printf("|%c|\n", shm[shm_v[1]].board[i][j]);
                  }
            }
      }
}


void new_player(){
      for (size_t i = 0; i < 6; i++) {
            for (size_t j = 0; j < 6; j++) {
                  shm[shm_v[1]].board[i][j] = '*';
            }
      }
}


int main(int argc, char *argv[]) {
      int id_shm, id_shm_v;


      id_shm  = shmget(SHM_KEY, SHMEM_SIZE, 0777 | IPC_CREAT);
      id_shm_v  = shmget(SHM_V_KEY, SHMEM_SIZE, 0777 | IPC_CREAT);


      if (id_shm == -1 || id_shm_v == -1) {
            perror("No se pudo reservar la memoria");
            exit(-1);
      }


      shm = (player *) shmat(id_shm, 0, 0);
      shm_v = (int *) shmat(id_shm_v, 0, 0);




      if(shm == -1 || shm_v == -1){
            perror("No se pudo acceder a la memoria");
            exit(-1);
      }
      new_player();
      print_player(&shm[shm_v[1]]);
      shm_v[1]++;


      //fill_matrix();
      //print_player(&shm[shm_v[1]]);


      while (1) {
            printf("Id del servidor: %d, cantida de jugadores actualmente %d\n", shm_v[0],shm_v[1]);
            sleep(2);
      }


      //shmdt(shm); //
      //shmctl(id_shm, IPC_RMID, 0);
}

Originally Posted by Salem

Code:

                  printf("|%c", shm[shm_v[1]].board[i][j]);
                  if (j == 5) {
                        printf("|%c|\n", shm[shm_v[1]].board[i][j]);
                  }

Because you always print the last column twice.

Also, storing a thread id in shared memory doesn't buy you anything. The result isn't usable in any other process context.

really thank you buddy that was the thing -.-
about the thread id you mean the shv_v[0]? im doing this to know who is the server process so i can send from other process signals