std::string str;

std::string::iterator i1 = str.begin();
auto i2 = str.begin();

std::basic_string<char,std::char_traits<char>,std::allocator<char> >::iterator i1

std::_String_iterator<std::_String_val<std::_String_base_types<char,std::allocator<char> >::_Val_types>::_Myt> i2

class A
{
    void f();
};

int main()
{
    auto a = A();
    return 0;
}

auto i = 3;    // Deduces int
auto d = 3.0;  // Deduces double
auto f = 3.0f; // Deduces double - wrong