CODEWITHSUNDEEP
c++stl
NeonGlow
NeonGlow

Reputation: 1692

Specifying STL Map key with 3 components

I am fairly new to STL. So pardon me if the question is naive.

I have a pair like this that is used as a key to a map.

typedef pair <int, int> KeyPair;

My map is as shown below

typedef map <KeyPair, uint32> NvInfoMap;

Now I want to introduce a new integer into the Key part of the map.

Which is the easiest way to do this?

Do I have to make another pair that will take the existing pair as its latter part?

Please note that I am on a restricted environment where boost library is not available.

Thanks for your time.

Upvotes: 2

Views: 2098

Answers (1)

Mike Seymour
Mike Seymour

Reputation: 254751

If your restrictions allow C++11, then

typedef std::tuple<int, int, int> KeyTriple;

Otherwise, you could define your own type

struct KeyTriple {
    int a;
    int b;
    int c;
};

with an ordering to allow it to be used as a key

bool operator<(KeyTriple const & lhs, KeyTriple const & rhs) {
    if (lhs.a < rhs.a) return true;
    if (rhs.a < lhs.a) return false;
    if (lhs.b < rhs.b) return true;
    if (rhs.b < lhs.b) return false;
    if (lhs.c < rhs.c) return true;
    return false;

    // Alternatively, if you can use C++11 but don't want a tuple for a key
    return std::tie(lhs.a, lhs.b, lhs.c) < std::tie(rhs.a, rhs.b, rhs.c);
}

or, as you suggest, you could use a nested pair

typedef std::pair<int, std::pair<int, int>>;

with the advantage that it defines the necessary comparison operator for you, but the disadvantage that creating one and accessing its elements is a bit of a faff.

Upvotes: 6

Related Questions