Why capacity changes for bool but not for int

Question

Please refer code below :

Capacity and size should be same for vector as I just have initialized data.

When checked size and capacity for vector of int, it is three as expected

This is not true for bool.... Why am I getting size as 64 intead of 3 for vBool ?
https://code.sololearn.com/cNBnY9fKP1Bo/?ref=app

Answer 1

Hm, interesting. I did some research and it seems that vector<bool> is a specialized template that is stored differently than other vectors.

1 boolean in C++ is actually 8 bit long for technical reasons. However, vector<bool> is a special structure optimized to store 1 boolean value per bit, so it can store 8 as many boolean values.
The structure used internally to solve this is 64 bits large, so the capacity of vector<bool> will always be a multiple of 64.