Hash function to switch on a string

Bonjour friends,

I am trying to get to work a switch on a string in C++, with the help of a hash. It became personal between me and this code, so I don't wanna give up and use an enum, even though I finally have only like 8 strings to put in switch cases.

Combining what I saw on other topics, I wrote this very simple and not so reliable function, but that is enough for what I want to do, as it's not professional.

My function :

constexpr long hashstr (const string &str, int h=0)
{
    return !str[h] ? 55 : ( hashstr(str, h+1) *33) + (unsigned char)str[h];
}

I then call it in this very simple main function (for now), but it won't compile, telling me that the case is wrong (not a constant). I don't understand this issue, as for me the string taken in arg is a constant, plus the function returns a constant expression.

My main :

int main (void) {

    string teststr;
    cout << "test string :::>  ";
    cin >> teststr;
    int tt = hashstr(teststr);
    cout << "res -->  " << tt << endl;

    switch ( hashstr(teststr) )
    {
    case hashstr("rosathefloridaturtle") :
        cout << "ROSA OK" << endl;
        break;

    default:
        cout << "ERROR" << endl;
        break;
    }

    return EXIT_SUCCESS;
}

Hoping that some of you can tell me what I'm not doing right...

Thank you by advance and greeting from France,

Haughty hi from Rosa the turtle,

SB