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#include <iostream>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <cstdlib>
#include <cstring>
#include <errno.h>
 
using namespace std;
 
static void usage(const char *progname);
 
int
main(int argc, char *argv[]) {
 
  if (argc != 2)
    usage(argv[0]);
 
  int key = atoi(argv[1]);
 
  int semid = semget(key, 1, 0660 );
 
  if (semid == -1) {
    cerr << "Error abrir el semaforo: " <<
      strerror(errno) << endl;
    return EXIT_FAILURE;
  }
 
  for (;;) {
    struct sembuf op[1];
 
    op[0].sem_num = 0;
    op[0].sem_op = -1;
    op[0].sem_flg = 0;
 
    cout << "Esperando para imprimir" << endl;
    semop(semid, op, 1);
    cout << "Impresion lista" << endl;
  }
 
  return EXIT_SUCCESS;
}
 
static void usage(const char *progname) {
  cerr << "Uso: " << progname << " <semkey> "
       << endl;
  exit(EXIT_FAILURE);
}