Vector and Class Relationship Confusion

Question

I posted the code here:
https://www.sololearn.com/post/419897/?ref=app

Answer 1

If you look at std::vector constructor definitions, the fill constructor, vector(n, val):

"... Constructs a container with n elements. Each element is a *copy* of val."

What vector<A> v(5,1) does, is create a vector of 5 elements of type class A, each initialized using the value 1.

http://www.cplusplus.com/reference/vector/vector/vector/

In this case, it appears that the fill constructor initializes one instance of class A, and makes 5 copies of the same object which fills the vector. Hence, the destructor was called once for that object, incrementing A::cnt by 1. Interesting!

Consider the example of not using the fill constructor:

vector<A> v = {A(1), A(1), A(1), A(1), A(1)};

In this case, 5 distinct temporary objects were created, and the destructor will be called five times in total, resulting in the value of A::cnt being 5.

https://code.sololearn.com/c9oyM2cdqrS1/?ref=app

Answer 2

Oh thanks @Hatsy Rei! :D

Answer 3

Is it because the class is called once by initiating vector<A>?