Непонятные функции std::vector

        vector<int> vec(30,444);//10 элементов, значение 7
    cout <<"vec.size()= "<<vec.size()<<endl;//30
    cout <<"vec.capacity()= "<<vec.capacity()<<endl;//30
    
        vec.reserve(35);//увеличивает емкость 
    cout <<"vec.size()= "<<vec.size()<<endl;//30
    cout <<"vec.capacity()= "<<vec.capacity()<<endl;//35
 
        vec.reserve(35);//увеличивает емкость 
    cout <<"vec.size()= "<<vec.size()<<endl;//30
    cout <<"vec.capacity()= "<<vec.capacity()<<endl;//35

#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v;
    v.resize(100);
    v.reserve(400);
    std::cout << sizeof(v) << std::endl;
 
    return 0;
}

    vector<int> v;
    cout <<v.size()<<' '<<v.capacity()<<endl;
    v.reserve(10);
    cout <<v.size()<<' '<<v.capacity()<<endl;
    cout <<sizeof(v)<<endl;//20
    vector<int> v1(10);
    cout <<sizeof(v1)<<endl;//20

vector<int> v(20);
cout << v.capacity() * sizeof(int);

/**  Returns the number of elements in the %vector.  */
size_type
size() const _GLIBCXX_NOEXCEPT
{ return size_type(this->_M_impl._M_finish - this->_M_impl._M_start); }
 
/**
 *  Returns the total number of elements that the %vector can
 *  hold before needing to allocate more memory.
 */
size_type
capacity() const _GLIBCXX_NOEXCEPT
{ return size_type(this->_M_impl._M_end_of_storage
                   - this->_M_impl._M_start); }