std::type_index (3) Linux Manual Page

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

                      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==
operator!= compares the underlying std::type_info objects
operator< (public member function)
operator<=
operator>
operator>=
                      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)
(C++11)

Example

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';
}

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)