Use data type (class type) as key in a map

Question

I have class Base and classes Derived_1, Derived_2 ... I need derived classes to have an id. Those ids are used for further lookups et

Answer 1

C++11 solves this by providing std::type_index, in , which is a copyable, comparable and hashable object constructed from a std::type_info object that can be used as the key in associative containers.

(The implementation is fairly simple, so even if you don't have C++11 yourself, you could steal the implementation from, say GCC 4.7, and use that in your own code.)

#include 
#include 
#include 

typedef std::unordered_map tmap;

int main()
{
    tmap m;
    m[typeid(main)] = 12;
    m[typeid(tmap)] = 15;
}