C++ boost unordered_map - 确定容器中是否存在键

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

提问by gewizz

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

在boost::unordered_map如何确定某个键存在与否？

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 '=='..."

上面得到编译器错误“不匹配运算符'=='...”

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

我使用的是自定义值类型还是其他问题？

回答by Luká? Lalinsky

You can use the findmethod:

您可以使用以下find方法：

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

回答by dalle

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

exist()拼写count()为任何关联容器：

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

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