Question

Let’s say you have a type T and subtypes TSub1, TSub2 etc.

Several of these subtypes are initialised with new TSub(...). The resulting pointers are then stored as elements in:

list<T*> tsList;

The same pointers are also used as keys in:

map<T*,V> tsMap;

Now consider an iteration over tsList, with iterator variable tIter.

Here are my questions:

1. Will tsMap[*tIter] and tsMap.find(*tIter) both successfully
   find the correct associated value?

2. Will delete *tIter successfully free the full memory block
   allocated for the relevant TSub even though STL sees the type as
   T?

3. Assume there is a defined method T::foo() and override TSub::foo().

   Will (*tIter)->foo() call T::foo() or TSub::foo() ?

The context is: each TSub is desired to be instantiated in singleton fashion, yet be stored in a manner allowing iterative consideration as the supertype, with methods overridden in the subclass being called.

I’d be very grateful for an informed explanation. Thank you for your time!

Answer 1

Will tsMap[*tIter] and tsMap.find(*tIter) both successfully find the
correct associated value?

Yes, but tsMap[*tIter] will create a default value if it doesn’t find the key.

Will delete *tIter successfully free the full memory block allocated
for the relevant TSub even though STL sees the type as T?

If and only if the destructor of T is virtual

Assume there is a defined method T::foo() and override TSub::foo().

Will (*tIter)->foo() call T::foo() or TSub::foo() ?

It will call T::foo if T::foo is not virtual. Otherwise it will call TSub::foo()