Hey friends please explain me this code and say how <vector> works ?And why output is 6?below

Question

#include <iostream>
#include <vector>
using namespace std;
class A{
public :
static int cnt;
A(int a){}
~A(){ ++cnt;}

};
int A::cnt =0;

int main() {
vector <A> v(4,1);
v.push_back(1);
cout<<A::cnt<<endl;
return 0;
}

//output is 6;

Answer 1

KrOW Nice explanation

Answer 2

Albert Whittaker :Fan Of😍 Motu Patlu😍 This is the logic:

1) at "v" construction a temporary "A" object will be created from casting second param (1) in an "A" object... Because its a temporary object, destructor will be called and "cnt" incremented (after this line, "cnt" is 1)

2) On
push_back call, you have "v" with 4 items and because you have not setted an larger capacity, it will resize if grow. This mean that if "v" grows, all items going copied in a a new "space" and old item deallocated. Then, on push_back two things happens: first is created a temporary "A" object (destroyed at end of statement), second push_back copy/allocate and destroy old 4 items. Because of this "cnt" will be incremented 4 (deallocation old items) + 1 (temporary object deallocation) = 5 times and added to previous "cnt" value (1) it will be 6

I hope that i been clear.. If not please ask

Answer 3

Ketan Lalcheta Thank you 😊😊😊