Superfluous clearing of containers

[heplesser]

As noticed by @diesmann and @mlober, the (*it)->clear() calls in the code below are most likely superfluous, since the vector pointed to by it is deleted immediately afterwards:

nest-simulator/nestkernel/event_delivery_manager.cpp

Lines 119 to 131 in d70928e

	for ( auto it = emitted_spikes_register_.begin(); it < emitted_spikes_register_.end(); ++it )
	{
	( *it )->clear();
	delete ( *it );
	}
	emitted_spikes_register_.clear();
	for ( auto it = off_grid_emitted_spikes_register_.begin(); it < off_grid_emitted_spikes_register_.end(); ++it )
	{
	( *it )->clear();
	delete ( *it );
	}
	off_grid_emitted_spikes_register_.clear();

The loops would also become simpler and more robust using C++11-style container iteration.

[terhorstd]

The explicit clear() is necessary, because the vector contains explicit pointers to inner vectors. The delete removes all elements of the outer vector (pointers!), but the inner vector instances need to have their elements removed before the pointer is deleted.
Note that the clear() call does a double "dereferencing": it is the iterator, *it is a pointer and -> dereferences to the vector<>.

[heplesser]

@terhorstd I don't quite agree with your analysis. We have

std::vector< std::vector< SpikeDataWithRank >* > emitted_spikes_register_;

and

auto it = emitted_spikes_register_.begin();

so *it gives us the first element of the outer vector, i.e., a pointer to an std::vector<SpikeDataWithRank> object. The entries in this vector are non-pointer entries, and (*it)->clear() clears these entries. Afterwards,

delete (*it);

destroys the std::vector<SpikeDataWithRank> object that *it points to. In my understanding of C++ containers, deleting a container that contains only non-pointer objects, will properly delete all objects contained in the container, i.e., call their destructors, before deleting the container itself. Therefore, the (*it)->clear() is superfluous. Afterwards,

emitted_spikes_register_.clear(); 

removes the now invalid pointers.

[terhorstd]

After our discussion we concluded that indeed this should also do:

 for ( auto vec_spikedata_ptr : emitted_spikes_register_ ) 
 { 
   delete vec_spikedata_ptr; 
 } 
 emitted_spikes_register_.clear(); // remove stale pointers