Inherit from another projects class

Question

Hello together,
I am new to Eclipse-CDT and I have the following Problem:
I have 2 C++-Projects im my Workspace,
now i want ClassB in Project 2 to inherite from ClassA in Project 1
I managed that by adding the Source-Path of Project 1 to the Include-List (Project2->Properties->Paths and Symbols->Include) of Project2
After that I am able to include the header for ClassA in my ClassB-Source.
But when i want to build Project2 i got the following Errors:
Quote:
Nicht definierter Verweis auf `ClassA::ClassA(char*)' ClassB.cpp /Project2/src/system line 16 C/C++ Problem
Nicht definierter Verweis auf `ClassA::~ClassA()' ClassB.cpp /Project2/src/system line 21 C/C++ Problem
Line 16 is the Call of the ClassB-Constructor,
Line 21 is the ClassB-Destructor:
ClassA - Header:
class ClassA
protected:
public:
ClassA(char *workingDir);
virtual ~ClassA();
ClassA - cpp:
ClassA::ClassA(char *workingDir)
ClassA::~ClassA()
ClassB - Header:
class ClassB : public ClassA
public:
ClassB(char *workingDir);
virtual ~ClassB();
ClassB - cpp:
ClassB::ClassB(char *workingDir) :
ClassA(workingDir) // Line 16 -> Nicht definierter Verweis auf `ClassA::ClassA(char*)' ClassB.cpp /Project2/src/system line 16 C/C++ Problem
ClassB::~ClassB() // Line21 -> Nicht definierter Verweis auf `ClassA::~ClassA()' ClassB.cpp /Project2/src/system line 21 C/C++ Problem
What is the Problem here?

Answer 1

Undefined reference (Nicht definierter Verweis) is a linker error. It means the linker couldn't find the object files defining ClassA members. If these are in a different project then you need a way to cause the linker to include the objects files from the project containing ClassA when linking executables using ClassB.
I realize this is vague but you apparently have code missing in your post. For example, how does ClassB know about ClassA in your ClassB - Header and ClassB - cpp and is there a main routine somewhere? Also, are these managed projects or makefile projects? It's difficult to know ahead of time what would be helpful, ain't it?
I tend to think of related projects as libraries for use by the project intended to produce main executable code. That means the "external" projects should be building link libraries. Perhaps the easiest way is to combine all of them into one project unless there is some pressing reason for keeping them separate.