Playing with shmat and shm_open

I just read the manpages for shm_open and shmat and was trying out the following example. In a file test.c I do,

int main(int argc, char **argv) {
  void *retval;
  long shmid = atol(argv[1]);

  retval = shmat(shmid, NULL, SHM_RDONLY);
  printf("%p\n", retval);
}

And in a wrapper file I do,

int setupshm(char *name) {
  int shmid;
  shmid = shm_open(name, O_CREAT|O_RDWR, 0666);
  return shmid;
}

int main() {
  char **envp = NULL;
  char *argv[3];
  char num[10];

  sprintf(num, "%d", setupshm("whatever"));

  argv[1] = "./test";
  argv[2] = num;
  argv[3] = NULL;

  execve("./test", argv, envp);
}

I tried adding in a strerror(errno) at test.c and I get Identifier removed. What does that mean? What am I doing wrong? Given a shared memory identifier(shmid), shouldn't I be able to access the shared memory from any process?