CODEWITHSUNDEEP
c++inheritancevirtual
zzzbbx
zzzbbx

Reputation: 10151

problem with inheritance

class OGraph {
public:
    OGraph() { }
    virtual ~OGraph();

    virtual bool is_directed()=0;
};

class OUGraph : public OGraph {
public:
    OUGraph() {  }
    bool is_directed() { return false; }
    ~OUGraph() {}
};

but when I do this

OUGraph myGraph();
cout << myGraph.is_directed();

I get the following error:

Undefined symbols: "typeinfo for OGraph", referenced from: typeinfo for OUGraphin main.o "vtable for OGraph", referenced from: OGraph::OGraph()in main.o mkdir -p dist/Debug/GNU-MacOSX "OGraph::~OGraph()", referenced from: g++ -o dist/Debug/GNU-MacOSX/opengraph build/Debug/GNU-MacOSX/OGraph.o build/Debug/GNU-MacOSX/main.o
OUGraph::~OUGraph()in main.o OUGraph::~OUGraph()in main.o ld: symbol(s) not found collect2: ld returned 1 exit status make[2]: * [dist/Debug/GNU-MacOSX/opengraph] Error 1 make[1]: [.build-conf] Error 2 make: ** [.build-impl] Error 2

BUILD FAILED (exit value 2, total time: 568ms)

Upvotes: 0

Views: 268

Answers (4)

Edward Strange
Edward Strange

Reputation: 40897

It's the same old thing all new C++ people fall for.

OUGraph myGraph();

You've not created a variable called myGraph, you've declared a function called myGraph that returns an OUGraph. Remove the "()".

You also apparently never defined your base's destructor anywhere. Even if it's empty you'll need to define it since you declared it in your class definition.

Upvotes: 2

fuzzyTew
fuzzyTew

Reputation: 3778

You have no implementation provided for virtual ~OGraph();. Either provide an implementation, specify it as pure virtual with = 0;, or just get rid of it.

The compiler is expecting to attach type info for the class to the implementation of its first virtual method. Your first virtual method is undefined, so the implementation is never generated, and you get related linking errors.

Additionally, as everyone is saying, you should remove the parentheses from your definition of myGraph.

Upvotes: 1

chustar
chustar

Reputation: 12465

If you're constructing a new object based using a 'default' constructor, I believe you call it without the empty parenthesis.

So, you would use OUGraph myGraph not OUGraph myGraph()

Upvotes: 0

Jim Buck
Jim Buck

Reputation: 20724

This:

OUGraph myGraph();

is declaring a function called myGraph that returns a OUGraph. You need to instead have:

OUGraph myGraph;

This declares a variable, as you intend.

Upvotes: 4

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