std::basic_string<CharT,Traits,Allocator>::capacity

#include <iomanip>
#include <iostream>
#include <string>

void show_capacity(std::string const& s)
{
    std::cout << std::quoted(s) << "   " << s.capacity() << ".\n";
}

int main()
{
    std::string s{"Exemplar"};
    show_capacity(s);

    s += "   .";
    show_capacity(s);

    s.clear();
    show_capacity(s);

    std::cout << "\n   ."
                 "\n:  :  :\n" << std::left;

    std::string g;
    auto old_cap{g.capacity()};

    for (int mark{}; mark != 5; ++mark)
    {
        while (old_cap == g.capacity())
            g.push_back('.');

        std::cout << std::setw( 9) << g.size()
                  << std::setw(10) << g.capacity()
                  << std::setw(12) << g.capacity() / static_cast<float>(old_cap) << '\n';

        old_cap = g.capacity();
    }
}