A question

Question

Why the answer is 6 not 5?

I won't write necessary headers, please don't say it will give an error.

class A{
public:
static int cnt;
A(int a){}
~A(){++cnt;}
};

int main(){
vector<A> v(4,1);
v.push_back(1);
cout<<A::cnt<<endl;
}

Answer 1

i think its the following reason, but i‘m not 100% sure. vector<A> v(4,1) creates 4 objects so 4 constructor calls
and v.push_back(1) creates a temporary object from 1 by calling the constructor, it gets passed by value to push_back, now the temporary object is no longer needed and gets deleted so 1 deconstructor call. so overall 5 constructor calls and 1 deconstructor call
by the way i think your constructor is incomplete

Answer 2

It seems so complex, because I couldn't understand how this vector class works. Thank you.