Question

I have some questions on using std::map:

1. Is using an enum as the key in std::map a good practice? Consider the following code:

   enum Shape{     Circle,     Rectangle };  int main(int argc, char* argv[]) {      std::map<Shape,std::string> strMap;      // strMap.insert(Shape::Circle,'Circle'); // This will not compile      strMap[Shape::Circle] = 'Circle';         // But this will work      return 0; } 

2. In the above example, why is the call to insert() generating a compiler error while the overloaded [] operator works correctly? Which of these methods is recommended for inserting items into a std::map?

3. I understand that when the find() method is used on the std::map class, it is not doing a sequential search in the container but doing some logarithmic search which will be much faster than sequential search. Is this understanding correct?

Answer 1

1. Having an enum as key_type is not bad by itself. (edit) But if you only use sequential enum-values, a std::vector with O(1) access is even better.
2. insert must be used like this: mapVar.insert(make_pair(key, value)); See also cppreference.com.
3. Yes, std::map has O(log(n)) lookup, as guaranteed by the standard, and this is faster than O(n) if n is sufficiently high.