Re: Can't understand this warning

[Ian Collins]

On 04/28/17 08:09 AM, Stefan Ram wrote:
> I tried to make all of my functions out-of-line, yet I still
> get the warning. Why? And what can I do to get rid of the
> warning?
>
> #include <initializer_list>
> #include <iostream>
> #include <memory>
> #include <ostream>
>
> struct B
> { void n() const;
> virtual void v() const ;
> virtual ~B(); };
>
> void ::B::n() const { ::std::cerr << "::B::n\n"; }
> void ::B::v() const { ::std::cerr << "::B::v\n"; }
> B::~B() = default;
>
> struct D : public B
> { void n() const;
> void v() const override;
> ~D() override; };
>
> void ::D::n() const { ::std::cerr << "::D::n\n"; }
> void ::D::v() const { ::std::cerr << "::D::v\n"; }
> D::~D() = default;
>
> int main()
> { ::D const d;
> ::B const * b = &d;
> b->n();
> b->v(); ::std::cerr << '\n';
> d.n();
> d.v(); ::std::cerr << '\n';
> b->::B::n();
> b->::B::v(); ::std::cerr << '\n';
> d.::D::n();
> d.::D::v(); ::std::cerr << '\n'; }
>
> main.cpp:6:8: warning: 'B' has no out-of-line virtual method definitions; its vtable will be emitted in every translation unit [clang-diagnostic-weak-vtables]
> struct B
> ^
>
> main.cpp:15:8: warning: 'D' has no out-of-line virtual method definitions; its vtable will be emitted in every translation unit [clang-diagnostic-weak-vtables]
> struct D : public B
> ^

Compiler bug?

--
Ian

[Scott Lurndal]

r...@zedat.fu-berlin.de (Stefan Ram) writes:
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>
> I tried to make all of my functions out-of-line, yet I still
> get the warning. Why? And what can I do to get rid of the
> warning?

First hit on a google search explains the warning message and its
associated cause quite clearly.

[Marcel Mueller]

On 27.04.17 22.09, Stefan Ram wrote:
> main.cpp:6:8: warning: 'B' has no out-of-line virtual method definitions; its vtable will be emitted in every translation unit [clang-diagnostic-weak-vtables]
> struct B

Some compilers have the quirk to create the vtable for a polymorphic
class only by the compilation unit which implements the first virtual
function rather than by every compilation unit with weak symbols. This
does not work if there is no such function.


Marcel