std::type_index (3) - Linux Manuals

std::type_index: std::type_index


std::type_index - std::type_index


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

                      constructs the object
constructor (public member function)

destructor destroys the type_index object
                      (public member function)
(implicitly declared)

operator= assigns a type_index object
                      (public member function)
(implicitly declared)

operator!= compares the underlying std::type_info objects
operator< (public member function)
                      returns hashed code
hash_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
                           (class template specialization)


The following program is an example of an efficient type-value mapping.
// Run this code

  #include <iostream>
  #include <typeinfo>
  #include <typeindex>
  #include <unordered_map>
  #include <string>
  #include <memory>

  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';


  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.