C++ long error message i cannot resolve

Question

I get this message and it just goes on and on for ages and I can't see why. It says there is a problem with the template usage maybe but I don't think I did something wrong:

using std::shared_ptr;
using std::set;

class User{
    set<CoinBalance> holdings;
    ApiConnection api;

public:
    void newHolding(const shared_ptr<Coin>&, double amount = 0);
    void addToHolding(const shared_ptr<Coin>&, double amount = 0);
    void decreaseFromHolding(const shared_ptr<Coin>&, double amount = 0);

    double getHondingsUsdValue();
};

and this is how I used shared_ptr:

class CoinBalance {
    shared_ptr<Coin> coin;
    double amount;
};

Please, can you provide thee error message in a snippet instead of an image ? — Alex Placet, Jul 27 '18 at 07:58
Going out on a limb, it looks like `std::set` requires a less compare (< operator) on `CoinBalance`, which isn't there by default. — 500 - Internal Server Error, Jul 27 '18 at 08:01
Your `CoinBalance` class probably needs an `operator<` member since you're creating an `std::set` of them. — G.M., Jul 27 '18 at 08:01
but i overloaded == and != isn't it enough for the set to compare? — Dr. Prof. Patrick, Jul 27 '18 at 08:22
no, becase set uses tree structure internally so less-than is required. you can try hash_set instead, but that needs equality operator and hash function. — Hitobat, Jul 27 '18 at 08:27
Look up "strict weak ordering" and see also https://stackoverflow.com/questions/979759/operator-and-strict-weak-ordering — Jesper Juhl, Jul 27 '18 at 10:09

score 1 · Answer 1 · answered Jul 27 '18 at 09:39

1

yes, you need to implement the < operator for CoinBalance

answered Jul 27 '18 at 09:39

VinuT

11
1

score 0 · Answer 2 · answered Jul 27 '18 at 08:28

0

I think you have to implement the operator '<' for class CoinBalance.

answered Jul 27 '18 at 08:28

Stoica Mircea

782
10
22

C++ long error message i cannot resolve

2 Answers2