c++ - Using const char* as key for map/unordered_map

Question

How to create map/unordered_map that will use const char* as key directly?

If I use map<std::string,..>, then on each resolving map["abc"] = ... a new std::string object will be created. That causes a big overhead for allocating memory, creating a string object and copying the string into it.

How do I declare a map object that uses const char* directly without any overhead?

Answer 1

You can use a std::string_view:

std::map<std::string_view, int> Map;
Map["abc"] = 1; // no allocation necessary to store "abc"

It is basically a wrapper around string objects. And it's a view, which means that it doesn't own the string and thus doesn't copy and allocate memory to store a string.

Note that for small strings (and also literals), std::string doesn't allocate too due to SSO and so the overhead is minimal. Always measure before optimizing.