Thread: Converting to values in an Enum Type

  1. #1
    Registered User
    Join Date
    Nov 2012

    Converting to values in an Enum Type


    I am trying to define a card class for a card game and am having trouble connecting the values provided to the constructor to some predefined enum types.

    If I defined two enum types to be:

    enum Rank {Two, Three, [..other cards..] Jack, Queen, King, Ace};
    enum Suit {Spades, Diamonds, Clubs, Hearts};
    And a constructor which took in two chars representing the rank and the suit (because the user would enter it this way via standard input):

    Card (Rank r, Suit s);

    e.g. Card(J,D) -> Is internally equivalent to Card(Jack, Diamonds)

    How do I make that connection?

    I am also given:

    string Card::RankName = "23456789TJQKA";
    string Card::SuitName = "SDCH";
    Any help would be much appreciated!

  2. #2
    Registered User
    Join Date
    Jun 2005
    All sorts of ways. Probably the simplest is to create a second constructor that accepts two char's and does the mapping. With C++-11 you can use a delegating constructor. If your compiler does not support delegating constructors, simply use a (private) helper function that can implement the common details from both constructors.

    If you're happy to expose the user of your class to the need for mapping (which is rarely a good idea, and more indicative of a lazy programmer than anything else) create a helper function so they can create a Card using Card(MapRank('J'), MapSuit('D'));

    Actually doing the mapping (eg switch statements, or by using std::map's) is implementation detail.
    Right 98% of the time, and don't care about the other 3%.

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  3. #3
    Frequently Quite Prolix dwks's Avatar
    Join Date
    Apr 2005
    One easy way to do the conversion from char to enum value is
    Rank rankFromChar(char r) {
        return static_cast<Rank>(RankName.find(r));
    Since RankName is a string, you can find the position of r in the string, and cast that index to an enum value.

    This is without error checking. You may also want to make sure the position isn't std::string::npos, which would mean the character wasn't found....

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