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| Member functions | ||||
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type_info::hash_code (C++11) | ||||
std::size_t hash_code()constnoexcept; | (since C++11) | |
Returns an unspecified value (here denoted byhash code) such that for allstd::type_info objects referring to the same type, theirhash code is the same.
No other guarantees are given:std::type_info objects referring to different types may have the samehash code (although the standard recommends that implementations avoid this as much as possible), andhash code for the same type can change between invocations of the same program.
Contents |
(none)
A value that is identical for allstd::type_info objects referring to the same type.
The following program is an example of an efficient type-value mapping without usingstd::type_index.
#include <functional>#include <iostream>#include <memory>#include <string>#include <typeinfo>#include <unordered_map> struct A{virtual ~A(){}}; struct B: A{};struct C: A{}; using TypeInfoRef=std::reference_wrapper<conststd::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 Astd::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 intd is doublea is A*b is B*c is C
(removed in C++20) | checks whether the objects refer to the same type (public member function)[edit] |
| implementation defined name of the type (public member function)[edit] |
