std::type_index

性病：：类型[医]指数

Defined in header
class type_index;		(since C++11)

大type_index类的包装器类。std::type_info对象，可用作关联和无序关联容器中的索引。与...的关系type_info对象是通过指针维护的。type_index是CopyConstructible和CopyAssignable...

成员函数

(constructor)	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)
operator==operator!=operator<operator<=operator>operator>=	compares the underlying std::type_info objects (public member function)
hash_code	returns hashed code (public member function)
name	returns implementation defined name of the type, associated with underlying type_info object (public member function)

帮助者类

std::hash (C++11)	hash support for std::type_index (class template specialization)

例

下面的程序是一个有效的类型值映射的示例。

二次

#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';
}

二次

产出：

二次

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

二次

另见

type_info	contains some type's information, generated by the implementation. This is the class returned by the typeid operator. (class)

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