This is probably really simple, but I can't find a simple example for it. I understand that with a hash_multimap you can have several values mapped to a single key. But how exactly would I access those values. All the examples I stumbled across always just access the first value mapped to the the key. Heres an example of what I mean
key : value
1 : obj1a;
2 : obj2a, obj2b, obj2c
how would I access obj2b and obj2c, not just obj2a
The usual multimap iteration loop is like this:
#include <unordered_multimap>
typedef std::unordered_multimap<K, V> mmap_t;
mmap_t m;
for (mmap_t::const_iterator it1 = m.begin(), it2 = it1, end = m.end(); it1 != end; it1 = it2)
{
// outer loop over unique keys
for ( ; it1->first == it2->first; ++it2)
{
// inner loop, all keys equal to it1->first
}
}
To iterate over just one key value, use equal_range instead.
std::pair<mmap_t::const_iterator, mmap_t::const_iterator> p = m.equal_range(key);
for (mmap_t::const_iterator it = p.first; it != p.second; ++it)
{
// use "it->second"
}
For example, equal_range returns an two iterators, to the begin and end of the matching range :
void lookup(const map_type& Map, int key)
{
cout << key << ": ";
pair<map_type::const_iterator, map_type::const_iterator> p =
Map.equal_range(key);
for (map_type::const_iterator i = p.first; i != p.second; ++i)
cout << (*i).second << " ";
cout << endl;
}
where we're using a map_type like
class ObjectT; // This is the type of object you want to store
typedef hash_multimap<int, ObjectT> map_type;
Just grab an iterator to the first one and increment it. If the keys are still equal, you've got another entry with the same key value. You can also use equal_range.
