std::type_index(3)

NAME
std::type_index - std::type_index

Synopsis
   Defined in header <typeindex>
   class type_index; (since C++11)
   The type_index class is a wrapper class around a std::type_info object, that can be
   used as index in associative and unordered associative containers. The relationship
   with type_info object is maintained through a pointer, therefore type_index is
   CopyConstructible and CopyAssignable.

Member functions
   constructor constructs the object
                        (public member function)
   destructor destroys the type_index object
   (implicitly declared) (public member function)
   operator= assigns a type_index object
   (implicitly declared) (public member function)
   operator==
   operator!=
   operator<
   operator<= compares the underlying std::type_info objects
   operator> (public member function)
   operator>=
   operator<=>
   (removed in C++20)
   (C++20)
   hash_code returns hashed code
                        (public member function)
                        returns implementation defined name of the type,
   name associated with underlying type_info object
                        (public member function)

Helper classes
   std::hash<std::type_index> hash support for std::type_index
   (C++11) (class template specialization)

Example
   The following program is an example of an efficient type-value mapping. // Run this code
 #include <iostream>
 #include <memory>
 #include <string>
 #include <typeindex>
 #include <typeinfo>
 #include <unordered_map>
 struct A
 {
     virtual ~A() {}
 };
 struct B : A {};
 struct C : A {};
 int main()
 {
     std::unordered_map<std::type_index, std::string> type_names;
     type_names[std::type_index(typeid(int))] = "int";
     type_names[std::type_index(typeid(double))] = "double";
     type_names[std::type_index(typeid(A))] = "A";
     type_names[std::type_index(typeid(B))] = "B";
     type_names[std::type_index(typeid(C))] = "C";
     int i;
     double d;
     A a;
     // note that we're storing pointer to type A
     std::unique_ptr<A> b(new B);
     std::unique_ptr<A> c(new C);
     std::cout << "i is " << type_names[std::type_index(typeid(i))] << '\n';
     std::cout << "d is " << type_names[std::type_index(typeid(d))] << '\n';
     std::cout << "a is " << type_names[std::type_index(typeid(a))] << '\n';
     std::cout << "*b is " << type_names[std::type_index(typeid(*b))] << '\n';
     std::cout << "*c is " << type_names[std::type_index(typeid(*c))] << '\n';
 }

Output:
 i is int
 d is double
 a is A
 *b is B
 *c is C

See also
             contains some type's information, generated by the implementation.
   type_info This is the class returned by the typeid operator.
             (class)