Cast two pointers to a pointer of std::pair like struct-CodePudding

I have the following simple struct that resembles std::pair. I want to cast two pointers keys and Values to a pointer of the pair. How can I do this?

Thanks!

K* keys;
V* Values;
/*  
length of keys = length of Values
goal: operation(keys, Values) ---> pair*
*/
template <typename K, typename V, K EmptyKey = K(-1)> struct pair {
    K first;
    V second;
    static constexpr auto empty_key = EmptyKey;
    bool empty() { return first == empty_key; }
  };

CodePudding user response：

You have to copy the keys and values into the pairs.

template <typename K, typename V>
pair<K, V>* KVToPairs(const K* k, const V* v, unsigned int length) {
    if (!k || !v) {
        return nullptr;
    }

    pair<K, V>* pairs = new pair<K, V>[length];
    for (unsigned int i = 0; i < length;   i) {
        pairs[i].first = *(k   i);
        pairs[i].second = *(v   i);
    }
    return pairs;
}

See demo

If you dont want the copy. Maybe you should change the definition of pair, like

template <typename K, typename V, K EmptyKey = K(-1)> struct pair {
    const K* first = nullptr;
    const V* second = nullptr;
    static constexpr auto empty_key = EmptyKey;
    bool empty() { return !first || *first == empty_key; }
};

The KVToPairs function is almost the same other than the pairs assignment part.

See demo