检索STL映射键

Question

有没有办法（除了存储密钥作为值的一部分并迭代地图）从STL地图中检索密钥，multimap（hash_map）a la Perl密钥（％hash）？

Answer 1

for (std::map<key, value>::iterator iter = m.begin(); iter != m.end(); ++iter)
    iter->first; // this is the key

Answer 2

You can use a for loop.

for (const auto & keyVal : myMap)
    keyVal.first;

Answer 3

If you often need to get those keys (like in a big loop) then you might be interested in using boost::bimap . Otherwise you can use Nikola's solution that is correct.

Sometimes I put keys copies in another container when adding elements to a map. It require to be sure to synchronize the two containers but if it's isolated enough (in a class) then it's easy to setup.