C++ boost unordered_map - determine if key exists in container

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-exis开发者_JS百科tent 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?

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You can use the find method:

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

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exist() is spelled count() for any associative container:

if (my_hash_map.count(key)) { /*key exist*/ }

if (!my_hash_map.count(key)) { /*key does not exist*/ }