Why does this virtual destructor trigger an unresolved external?

Question

Consider the following:

In X.h:

class X
{
    X();
    virtual ~X();
};

X.cpp:

#inclu         


        

Answer 1

I have a suspicion on this one that this is implementation defined behavior. Here's why

$10.3/8- "A virtual function declared in a class shall be defined, or declared pure (10.4) in that class, or both; but no diagnostic is required (3.2)."

GCC gives error such as below, which again, is highly suggestive (to me at least) about a non-standard implementation detail of implementing virtual functions

/home/OyXDcE/ccS7g3Vl.o: In function X::X()': prog.cpp:(.text+0x6): undefined reference tovtable for X' /home/OyXDcE/ccS7g3Vl.o: In function X::X()': prog.cpp:(.text+0x16): undefined reference tovtable for X' collect2: ld returned 1 exit status

I am confused if a diagnostic is really required from a compiler for the OP code, so thought of posting this, even as I risk downvotes :). Of course, a good compiler should I guess.