std::map<int, int> m;

std::map<int, int>::const_iterator GetIterator()
{
    return m.begin();
}

const int &GetReference()
{
    return m[0];
}

int main()
{
    m[0] = 9999;
    
    std::map<int, int>::const_iterator it = GetIterator();
    std::cout << it->second << std::endl;

    const int& i = GetReference();
    std::cout << i << std::endl;
     
    return 0;
} 

9999
9999