Re: How to provide the implementation for a pure virtual dtor in the header file
On 30 Mrz., 17:47, Andrew <marlow.and...@googlemail.com> wrote:
I am getting a syntax error during compilation that I don't quite
understand. It is for a pure virtial dtor on an abstract base class.
The class is supposed to be pure interface, i.e. no implementation at
all. Hence all that should be needed by users of this class is to
include the header. There is no library.
But as we know, there has to be an implementation of the dtor. So I
have declared it inline like this:
class CMSMessage
{
public:
virtual ~CMSMessage() = 0 {};
};
With Visual Studio this compiles ok but with GCC I get the error
below:
CMSMessage.h:11: error: pure-specifier on function-definition
Gcc is correct. The language does not support to combine a pure
virtual function declaration and an function definition in a single
member declaration.
I can make the error go away by removing the inline curlies and
adding:
inline
CMSMessage::~CMSMessage()
{
}
to the header.
That is a portable way to realize that.
But is GCC correct to complain as it does? Can someone explain why
please?
The grammar discriminates among a /function-definition/ and
/member-declarator-list/ (and others). The usage of the grammar
element /pure-specifier/ is only feasible for a /member-declarator/.
Dtors have to have implementation but it is also possible to provide
implementation for other pure virtual methods and to call them. ISTR
an example of this in one of the Meyer books. This is what makes me
suspect that the GCC behaviour may be wrong here.
No, gcc is strictly conforming in this regard.
HTH & Greetings from Bremen,
Daniel Kr?gler
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