How do I insert elements into an unordered map in C++11?

How do I insert elements into an unordered map in C++11?

In C++11, you can insert elements into an unordered map using the insert method or the subscript operator. For example:

#include <unordered_map>

std::unordered_map<int, std::string> myMap;
myMap.insert({1, "one"}); // Using insert
myMap[2] = "two"; // Using subscript operator

This will insert the key-value pairs into the unordered map.

What happens if I insert a duplicate key?

If you insert a duplicate key using the insert method, it will not overwrite the existing value, and the insertion will fail. However, if you use the subscript operator, it will overwrite the existing value with the new one.

Can I use custom types as keys in an unordered map?

Yes, you can use custom types as keys in an unordered map, but you need to provide a hash function and an equality function for your custom type. You can do this by specializing std::hash and defining the equality operator.

What are the advantages of using unordered_map over map?

The main advantage of using unordered_map is that it provides average constant time complexity for insertions, deletions, and lookups, while map has logarithmic time complexity. This makes unordered_map generally faster for these operations.