typeinfo

Typeinfo refers to the runtime type information available for objects in certain programming languages, most commonly in C++. In C++, the mechanism is provided by the type_info class and the typeid operator, and it is part of the broader runtime type information (RTTI) feature set.

The typeid operator yields a reference to a std::type_info object that describes the static or dynamic type of an expression or object. The primary means of accessing this information is typeid(x).name(), which returns an implementation-defined string representing the type. The actual content of the name is not portable across compilers, and human-readable names may require demangling on some platforms. The type_info objects can be compared for equality or inequality, and there is a before() function to impose an ordering suitable for use in associative containers.

A key aspect of typeinfo in C++ concerns polymorphism. If the expression is of a polymorphic class (one with virtual functions), typeid yields the dynamic type of the object at runtime. If the expression is non-polymorphic, typeid yields its static type. This distinction makes typeinfo useful for debugging, logging, or implementing simple type-based dispatch, but it should not be relied on for general program logic. For such purposes, dynamic_cast can also be used to test or convert types at runtime.

Limitations include the implementation-defined nature of type names and potential portability concerns between compilers and libraries. RTTI can be disabled in some environments, typically via compiler flags, which would render typeid and related features unavailable. typeinfo is primarily a C++ construct; other languages implement similar concepts under different names and APIs. See also typeid, std::type_info, and RTTI.