RTTI typeinfo pointers

[Asfand Yar Qazi]

Hi,

Will the std::type_info object returned by typeid be the same
object every time it is called for a given type?

Can there ever be a chance that a std::type_info object returned
by typeid for two different types will share the same memory
address? Lets say, for example, I want to use the address of the
type_info object as a hash value.

Thanks,
Asfand Yar

 

[tom_usenet]

Hi,

Will the std::type_info object returned by typeid be the same
object every time it is called for a given type?

No (specifically on Windows with a type defined both in a .exe and a
..dll), and the standard doesn't require it. The objects must compare
equal though, of course.

Can there ever be a chance that a std::type_info object returned
by typeid for two different types will share the same memory
address?

No, it wouldn't be conforming.

Lets say, for example, I want to use the address of the
type_info object as a hash value.

type_info objects work well in a sorted container, due to their
"before" member function. But hashing by pointer value should be
reliable on some platforms at least, just not guaranteed to work by
the standard, and it probably won't work on Windows.

Tom

 

[Asfand Yar Qazi]

type_info objects work well in a sorted container, due to their
"before" member function. But hashing by pointer value should be
reliable on some platforms at least, just not guaranteed to work by
the standard, and it probably won't work on Windows.

Tom

I'll just use a std::map then, thanks for that.