< cpp‎ | types‎ | type info
Type support
Basic types
Fundamental types
Fixed width integer types (C++11)
Numeric limits
C numeric limits interface
Runtime type information
Type traits
Type categories
Type properties
(C++11)(deprecated in C++17)
Type trait constants
Supported operations
Relationships and property queries
Type modifications
Type transformations
(C++11)(deprecated in C++17)(C++17)
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.


[edit] Parameters


[edit] Return value

A value that is identical for all type_info objects referring to the same type.

[edit] Example

The following program is an example of an efficient type-value mapping without using std::type_index.

#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';


i is int
d is double
a is A
b is B
c is C

[edit] See also

checks whether the objects refer to the same type
(public member function) [edit]
implementation defined name of the type
(public member function) [edit]