Avoid weak-vtable warnings for classes only defined in a source file

Question

I understand that a class class needs at least one virtual function defined in a source file (out of line), otherwise the vtable will need to be inserted into every object file.

I have the following situation:

//foo.cpp

struct Foo {
virtual int Bar() { return 1; }
virtual ~Foo() = default;
};

The clang code model in Qt Creator (4.5.2) emits a -Wweak-table warning for Foo.
Strictly speaking the warning is correct, as the vtable will be included in every translation unit. Practically, it's worthless because either way the vtable is only emitted in foo.o anyway.

How can I disable -Wweak-vtables only for classes defined in a source file?

does it do the same for classes in the local namespace? – bobah May 22 '18 at 08:47 — bobah, May 22 '18 at 08:47

score 3 · Accepted Answer · answered May 22 '18 at 09:49

It turns out that standalone clang does the right thing by default, only the clang code model in Qt creator shows the useless warning. It's already reported as QTCREATORBUG-19741, so there's nothing more to do than wait for an updated Qt creator version.

score 1 · Answer 2 · answered May 22 '18 at 09:26

Not really sure, but where I work, we have some practices for disabling warnings in localized sources.

Under windows:

#pragma warning(push)
#pragma warning(disable : 4820)
//Rest of your includes (cstdio, vector...)
#pragma warning(pop) //For /Wall

Under gcc like:

#pragma GCC diagnostic push 
#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
//Rest of your includes (cstdio, vector...)
#pragma GCC diagnostic pop

Avoid weak-vtable warnings for classes only defined in a source file

2 Answers2