std::type_info::hash_code
size_t hash_code() const; |
(since C++11) | |
Returns an unspecified value such that for all type_info
objects referring to the same type, their hash_code() is the same.
No other guarantees are given: type_info
objects referring to different types may have the same hash_code (although the standard recommends that implementations avoid this as much as possible), and hash_code for the same type can change between invocations of the same program.
Parameters
(none)
Return value
A value that is identical for all type_info
objects referring to the same type.
Example
The following program is an example of an efficient type-value mapping without using std::type_index.
Run this code
#include <iostream> #include <typeinfo> #include <unordered_map> #include <string> #include <functional> #include <memory> struct A { virtual ~A() {} }; struct B : A {}; struct C : A {}; using TypeInfoRef = std::reference_wrapper<const std::type_info>; struct Hasher { std::size_t operator()(TypeInfoRef code) const { return code.get().hash_code(); } }; struct EqualTo { bool operator()(TypeInfoRef lhs, TypeInfoRef rhs) const { return lhs.get() == rhs.get(); } }; int main() { std::unordered_map<TypeInfoRef, std::string, Hasher, EqualTo> type_names; type_names[typeid(int)] = "int"; type_names[typeid(double)] = "double"; type_names[typeid(A)] = "A"; type_names[typeid(B)] = "B"; type_names[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[typeid(i)] << '\n'; std::cout << "d is " << type_names[typeid(d)] << '\n'; std::cout << "a is " << type_names[typeid(a)] << '\n'; std::cout << "b is " << type_names[typeid(*b)] << '\n'; std::cout << "c is " << type_names[typeid(*c)] << '\n'; }
Output:
i is int d is double a is A b is B c is C
See also
checks whether the objects refer to the same type (public member function) | |
implementation defined name of the type (public member function) |