How to resolve this linking error

Question

I have a class A, that is an abstract base class.(C++). Now, I have two classes B and C which inherit from A;

I have a virtual destructor in A; The constructor in class A is protected. Now, in the constructors of B and C, I have included a call to A's constructor.

B::B():A()
{
//do something
}

similarly for C

C::C():A()
{
//do something
}

Now, while compiling I'm getting linking errors.

    B.obj : error LNK2019: unresolved external symbol "protected: __
thiscall A::A(void)" (??0A) referenced in function "protected: __thiscall B::B(void)" (??0B)

    C.obj : error LNK2001: unresolved external symbol "protected:
__thiscall A::A(void)" (??0A@XZ)
      Error.

Please suggest how to resolve this.

Thanks, Karhtik.

Post the full code. There's bound to be a bug in the code you're *not* showing us. — Kerrek SB, Aug 01 '11 at 16:47
Try to construct a minimal example that reproduces your problem. Otherwise there's no real question here. — n. m. could be an AI, Aug 01 '11 at 17:21

score 0 · Answer 1 · answered Aug 01 '11 at 16:41

0

This suggests that you never defined the default constructor of A when you declared it.

answered Aug 01 '11 at 16:41

Puppy

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@user815961: If it was "in place", you wouldn't be getting these linker errors. No, the constructor definition is not "in place" (whatever you mean by that "in place") – AnT stands with Russia Aug 01 '11 at 17:57
Hi all, actually, the abstract base class (A) has a constructor. And removing it from that abstract base class and all its child's (B & C) is resolving the issue. Is it that an abstract base class cannot have a constructor? http://stackoverflow.com/questions/1057221/what-are-practical-uses-of-a-protected-constructor – Pavan Dittakavi Aug 02 '11 at 04:25

score 0 · Accepted Answer · answered Aug 01 '11 at 16:52

Firstly, there's really no need to "call" the base class constructor explicitly. The default constructor of the base class will be called for you automatically.

Secondly, as @DeadMG already noted, the error you are getting suggests that you explicitly declared the A::A() constructor, but forgot to define it.

How to resolve this linking error

2 Answers2