C++ enum from char

Question

Ok, I'm new at C++. I got Bjarne's book, and I'm trying to follow the calculator code.

However, the compiler is spitting out an error about this section:

token_value get_token()
{
    char ch;

    do {        // skip whitespace except '\n'
        if(!std::cin.get(ch)) return curr_tok = END;
    } while (ch!='\n' && isspace(ch));

    switch (ch) {
        case ';':
        case '\n':
            std::cin >> WS;      // skip whitespace
            return curr_tok=PRINT;
        case '*':
        case '/':
        case '+':
        case '-':
        case '(':
        case ')':
        case '=':
            return curr_tok=ch;
        case '0': case '1': case '2': case '3': case '4': case '5':
        case '6': case '7': case '8': case '9': case '.':
            std::cin.putback(ch);
            std::cin >> number_value;
            return curr_tok=NUMBER;
        default:            // NAME, NAME=, or error
            if (isalpha(ch)) {
                char* p = name_string;
                *p++ = ch;
                while (std::cin.get(ch) && isalnum(ch)) *p++ = ch;
                std::cin.putback(ch);
                *p = 0;
                return curr_tok=NAME;
            }
            error("bad token");
            return curr_tok=PRINT;
}

The error it's spitting out is this:

calc.cpp:42: error: invalid conversion from ‘char’ to ‘token_value’

token_value is an enum that looks like:

enum token_value {
    NAME,       NUMBER,     END,
    PLUS='+',   MINUS='-',  MUL='*',  DIV='/',
    PRINT=';',  ASSIGN='=', LP='(',   RP=')'
};
token_value curr_tok;

My question is, how do I convert ch (from cin), to the associated enum value?

Answer 1

You can't implicitly cast from char to an enum - you have to do it explicitly:

return curr_tok = static_cast<token_value> (ch);

But be careful! If none of your enum values match your char, then it'll be hard to use the result :)