Question

Sometimes c++ plays me big time. I really can’t think of why this does/doesn’t work and I’d be happy if any of you knew.

I call this function once every second on a thread.

This code WORKS (prints what is on the list being iterated):

void DeltaList::print()
{
  pthread_mutex_lock (&mutex);
  printf("\n");
  list<Delta*>::iterator it;
  for(it=deltas.begin(); it!=deltas.end(); it++)
  {
    printf("%d   ", (int) (*it)->timeleft);
  }

  pthread_mutex_unlock (&mutex);
}

This one DOESN’T (nothing is printed):

void DeltaList::print()
{
  pthread_mutex_lock (&mutex);
  //printf("\n");
  list<Delta*>::iterator it;
  for(it=deltas.begin(); it!=deltas.end(); it++)
  {
    printf("%d   ", (int) (*it)->timeleft);
  }

  pthread_mutex_unlock (&mutex);
}

So… ?

Answer 1

This has nothing to do with threading or C++. The OS is buffering your output, and the \n implicitly flushes the buffer when stdout is a console. Call fflush(stdout) after the loop if you want every call to show its output immediately.