std::type_index - cppreference.com (original) (raw)
| | | | | ------------------ | | ------------- | | 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.
[edit] Member functions
| (constructor) | constructs the object (public member function) [edit] |
|---|---|
| (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) [edit] |
| hash_code | returns hashed code (public member function) [edit] |
| name | returns implementation defined name of the type,associated with underlying type_info object (public member function) [edit] |
[edit] Helper classes
[edit] Example
The following program is an example of an efficient type-value mapping.
#include #include #include #include #include #include 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 b(new B); std::unique_ptr 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
[edit] See also
| | contains some type’s information, the class returned by the typeid operator (class) [edit] | | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |