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You might think that similar amendments to the engine,
tank_car, and caboose classes would enable you to display car
names using a for loop such as the following:
for (n = 0; n < car_count; ++n) {
train[n] -> display_short_name ( );
cout << endl;
}
After all, train[n] picks a particular pointer out of the array, and
the class-pointer operator, ->, tells C++ to go through the
pointer to get at display_short_name, a member function defined in
the definitions of all four car types.
Your C++ compiler rejects the program, nevertheless. The
reason is that the train array is supposed to contain
pointers to railroad_car objects, and you have defined no
display_short_name function for railroad_car
objects. At compile time, the compiler has no clue that the
pointers in the train array may actually point to objects
that belong to subclasses for which the display_short_name
function is defined.