19.2.4. The type_info Class

The exact definition of the type_info class varies by compiler. However, the standard guarantees that the class will be defined in the typeinfo header and that the class will provide at least the operations listed in Table 19.1.

Table 19.1. Operations on type_info

The class also provides a public virtual destructor, because it is intended to serve as a base class. When a compiler wants to provide additional type information, it normally does so in a class derived from type_info.

There is no type_info default constructor, and the copy and move constructors and the assignment operators are all defined as deleted (§ 13.1.6, p. 507). Therefore, we cannot define, copy, or assign objects of type type_info. The only way to create a type_info object is through the typeid operator.

The name member function returns a C-style character string for the name of the type represented by the type_info object. The value used for a given type depends on the compiler and in particular is not required to match the type names as used in a program. The only guarantee we have about the return from name is that it returns a unique string for each type. For example:

int arr[10];
Derived d;
Base *p = &d;
cout << typeid(42).name() << ", "
     << typeid(arr).name() << ", "
     << typeid(Sales_data).name() << ", "
     << typeid(std::string).name() << ", "
     << typeid(p).name() << ", "
     << typeid(*p).name() << endl;

This program, when executed on our machine, generates the following output:

i, A10_i, 10Sales_data, Ss, P4Base, 7Derived