Question

I have some (working) code that uses a multimap<string,string>. I’d like to change it to disallow duplicate values on the same key (obviously different values on the same key are fine, otherwise I wouldn’t use a multimap).

Surprisingly the type doesn’t seem to have a built-in way to avoid duplicates nor to find a key-value pair (only to find a key). But I figure someone on SO must have a ready-made workaround. Anyone?

Answer 1

Here’s what I came up with:

template<class K, class V>
typename multimap<K, V>::const_iterator find_pair(const multimap<K, V>& map, const pair<K, V>& pair)
{
    typedef multimap<K, V>::const_iterator it;
    std::pair<it,it> range = map.equal_range(pair.first);
    for (it p = range.first; p != range.second; ++p)
        if (p->second == pair.second)
            return p;
    return map.end();
}
template<class K, class V>
bool insert_if_not_present(multimap<K, V>& map, const pair<K, V>& pair)
{
    if (find_pair(map, pair) == map.end()) {
        map.insert(pair);
        return true;
    }
    return false;
}

(This is not efficient when there are a large numbers of values attached to a single key, but in my case there are very few values on each key.)