std::type_index

 

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Runtime type information
type_info type_index (C++11)	bad_typeid bad_cast

 

std::type_index

Member functions

type_index::type_index

type_index::operator=type_index::operator!=type_index::operator<type_index::operator<=type_index::operator>type_index::operator>=type_index::operator<=> (until C++20)(C++20)

type_index::hash_code

type_index::name

Helper classes

hash<std::type_index> (C++11)

 

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

Helper classes

std::hash<std::type_index> (C++11)

hash support for std::type_index (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 Astd::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

type_info

contains some type’s information, the class returned by the typeid operator (class)