Understanding return value optimization and returning temporaries - C++

Please consider the three functions.

std::string get_a_string()
{
    return "hello";
}

std::string get_a_string1()
{
    return std::string("hello");
}

std::string get_a_string2()
{
    std::string str("hello");
    return str;
}

1. Will RVO be applied in all the three cases?
2. Is it OK to return a temporary like in the above code? I believe it is OK since I am returning it by value rather than returning any reference to it.

Any thoughts?