I’m adding a known number of elements to a std::vector and noticed that its capacity changes several times while inserting elements.

For example:

std::vector values;

for (int i = 0; i < 1000; ++i) {
    values.push_back(i);
}

I understand that std::vector grows its capacity automatically, but I’m trying to understand the practical difference between:

std::vector values;
values.reserve(1000);

and:

std::vector values(1000);

Specifically:

1. How does reserve() affect reallocations and object construction?

2. When should I use reserve() instead of creating the vector with an initial size?

3. Is the vector’s growth strategy defined by the C++ standard, or does it depend on the implementation?