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.
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) |
compares the underlying std::type_info objects (public member function) |
|
returns hashed code (public member function) |
|
returns implementation defined name of the type, associated with underlying type_info object (public member function) |
(C++11) | hash support for std::type_index (class template specialization) |
The following program is an example of an efficient type-value mapping.
#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
contains some type's information, generated by the implementation. This is the class returned by the typeid operator. (class) |
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