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The typeid operator in C++ returns an object of class std::type_info which can yield its textual name. However, I'm just interested in getting an unique numeric identifier for any polymorphic class. (unique in the scope of a single program run - not necessarily between runs)
In practice, I could just dereference the pointer and read the vptr's contents - but this would be neither elegant nor portable. I prefer a portable way.
Can I use the typeid operator somehow to have a "safe" numerical identifier for a class? For example, can I count on the address of resulting std::type_info structure to be the same for every typeid call on a given class? Or perhaps the name() pointer itself?
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Here's the simplest ID I can think of. MyObject obj; uint32_t id = reinterpret_cast<uint32_t>(&obj); At any given time, this ID will be unique across the application. No other object will be located at the same address.
The typeid operator provides a program with the ability to retrieve the actual derived type of the object referred to by a pointer or a reference. This operator, along with the dynamic_cast operator, are provided for runtime type identification (RTTI) support in C++.
Since typeid is applied to a type rather than an object, there is no runtime type information, so that overhead won't be a problem.
std::type_index (C++ 11) can be used in containers to store values based on type. It won't give you a number though.
std::type_index index = std::type_index (typeid (int));
More: http://en.cppreference.com/w/cpp/types/type_index
The
type_indexclass is a wrapper class around astd::type_infoobject, that can be used as index in associative and unordered associative containers. The relationship withtype_infoobject is maintained through a pointer, therefore type_index is CopyConstructible and CopyAssignable.
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