What information does RTTI store for a polymorphic object?

Question

Before I begin- I know that a polymorphic object has a vtable to select the correct method at runtime. However, is there any more additional information each polymorphic object contains (excluding the vtable)?

I am trying to measure the size/cost of a polymorphic object with RTTI enabled, compared with a non-polymorphic object. I only know about the vtable overhead and wondered what else is stored within RTTI.

EDIT: Lets say for the GCC compiler

Imagine that the compiler added a hidden function to the vtable: `GetAllRTTIdata`. Since the vtable only exists once per class and not once per object, and you're only adding a single entry to it, the overhead is nearly nonexistent. — Mark Ransom, Jan 04 '14 at 05:49

score 0 · Answer 1 · answered Jan 04 '14 at 02:23

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There may be an implementation-defined type name there, too (for std::type_info::name(), which can contain in theory absolutely anything), but otherwise it's pretty much just the vtable. Certainly I can't think of anything else that needs to be there in order to satisfy the rules of the language.

Not much more can be said in the general case; this is completely down to the implementation, and you didn't specify one. Some compiler could include a recipe for chicken soup if it really wanted to.

answered Jan 04 '14 at 02:23

Lightness Races in Orbit

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I found this which may help me: http://stackoverflow.com/questions/579887/how-expensive-is-rtti?rq=1 – user997112 Jan 04 '14 at 02:25
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@user997112: I'd have to examine GCC's source for that, which could take days. Why do you care? – Lightness Races in Orbit Jan 04 '14 at 02:25

What information does RTTI store for a polymorphic object?

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