Question

In boost::unordered_map how do I determine if a key exists in it or not?

boost::unordered_map<vector<int>, MyValueType> my_hash_map;

if (my_hash_map[non-existent key] == NULL)

The above gets compiler error “no match for operator ‘==’…”

Is the problem that I am using a custom value type or something else?

Answer 1

You can use the find method:

if (my_hash_map.find(non-existent key) == my_hash_map.end())