c++ stl: enclosing difficulty reuse after clearing?

in programming face several situations where mandatory middle stl containers following instance depicts:

while(true)
{
    set < int > tempset;

    (int i = 0; i < n; i ++)
    {
        (m.size() == min && m.size() <= max)
        {
            tempset.insert(i);
        }
    }
    //some condition contrast code
}

or

set < int > tempset;

while(true)
{
    (int i = 0; i < n; i ++)
    {
        (m.size() == min && m.size() <= max)
        {
            tempset.insert(i);
        }
    }
    tempset.clear();

    //some condition contrast code
}

which proceed improved terms space complexity deliberation donation state c++ compliers?