| 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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