While explicitly instantiating vector, what is the someType default constructor used for?

Question

It\'s an exercise from C++ Primer 5th Edition:

Exercise 16.26: Assuming NoDefault is a class that does not have a default constructor, can we e

Answer 1

While explicitly instantiating std::vector, what is the someType default constructor used for?

It's used to construct the elements of the array when resizing the std::vector. For example:

std::vector vector(10);

will default construct 10 elements of type T.