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Subject: [Bug other/42540] c++ error message [vtable undefined] is unhelpful
Date: Mon, 14 Mar 2022 17:22:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D42540

--- Comment #18 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Eyal Rozenberg from comment #16)
> The compiler could store information in the compiled object listing the
> virtual members for which no implementation was found, due to which reason
> the vtable was not defined already. In this specific example, storing the
> name of "A::B()" somewhere.

In every file that includes the header defining A?

Consider the case where you include the header in ten files, and define the
virtual functions in one of them. Nine out of ten files do not contain a
definitions of the virtual functions, so they would each contain the same i=
nfo
naming every virtual function in the class. Then do that for every polymorp=
hic
class in every object file. This is a lot more info being written out, and =
most
of it will never be used.

You have nine files saying "this function is missing" and one not saying it.
What exactly does the linker do with that information? Why would that be be=
tter
than comment 7 here?=