unresolved external symbol with no "referenced in" field

Question

So, usually when you see an Unresolved External Symbol error, the linker at least tells you what function the reference is in, i.e.

unresolved external symbol "class1::function1" **referenced in function "class2::function2"**

But what do you do when you only get the first half? i.e.

unresolved external symbol "class1::function1"

I know where "class1::function1" is defined, and I am deliberately not including it. So just including the file containing the definition won't help. The include is ifdef'd out, along with all references to symbols contained in the file. What I need is a way to locate the reference to this deliberately non-included symbol so that I can get rid of it. Searches for the name of the symbol reveal only things which I have already ifdef'd out.

Answer 1

This turns out to have been a combination of a mistake on my part, and a non-helpful error message. One of the classes was missing a member of it's inheritance chain.

Personally I would have expected this to result in a compiler error ("Extending Undefined Base Class" or something similar), but instead I got linker errors for the virtual functions in said base class (despite that class not being included). But because no functions were actually referencing them, the linker could not provide a "referenced in" section for the error message. I still don't entirely understand why this set of problems with the code gave that set of error messages, but I was able to fix it.

Thank you Alan for your input, it got me looking in the correct direction. I would upvote you, but having joined immediately before posting the question, I lack the reputation score to do so.

Answer 2

If it's a virtual function then it's referenced from the vtable, which in turn is referenced from each constructor (or each place where a constructor is inlined).

If you're using instances of the class I think your best bet is to remove the virtual keyword. Otherwise you must provide a definition, even if only a stub.

(The language standard handles this by considering any virtual function as always used, so a definition is required.)

Answer 3

I'm not sure why that happens, but easy way to determine source of problem is to comment out all declarations of class1::function1, and rebuild the project - compiler will complain whenever class1::function1 is called on compile stage instead of linking.