Pointers inside shared memory segment

Question

I\'ve been trying this for hours, and google all the things I kind think of, but I\'m going crazy.

I have a struct:

typedef struct {
  int rows;
  in         


        

Answer 1

ctrl = (mem *)shmat(shmemid, 0, 0); 

This only assigns valid memory to the ctrl pointer, not to ctrl->mat or ctrl->IDs_row.

You probably want:

mem *ctrl;
shmemid = shmget(KEY, sizeof(ctrl), IPC_CREAT | 0666);
//allocate memory for the structure
ctrl = (mem *)shmat(shmemid, 0, 0);

//allocate memory for the int*
shmemid = shmget(KEY,((i-1)*num_cons))*sizeof(int), IPC_CREAT | 0666);
ctrl->mat = (int*)shmat(shmemid, 0, 0);

//allocate memory for the char*
shmemid = shmget(KEY,i*26*sizeof(char), IPC_CREAT | 0666);
ctrl->IDs_row = (char*)shmat(shmemid,0,0);