Question

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

Answer 1

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"
}