undefined reference to vtable for inheriting classes - c++

Question

I'm trying to develop a neural network in c++.
I refactored my code utilizing class-inheritance, to allow me to have different kinds of layers, whose neurons could be iterated over in sequence.
My problem is, that my linker (ld invoked by g++) complaines about undefined references to vtables and typeinfo-objects.
As far as I know, the error "undefined reference to vtable for class" comes from not implemented pure virtual methods in base classes, but unfortunately I not was able locate the error more percisely.
make all:
g++ -Wall -fmessage-length=0 --std=c++11 -w -c -o Test2dSparselyNeuralNet.o Test2dSparselyNeuralNet.cpp
g++ -Wall -fmessage-length=0 --std=c++11 -w -c -o NeuralNet.o NeuralNet.cpp
g++ -Wall -fmessage-length=0 --std=c++11 -w -c -o Sparsely2dNeuralNetwork.o Sparsely2dNeuralNetwork.cpp
g++ -Wall -fmessage-length=0 --std=c++11 -w -c -o Connection.o Connection.cpp
g++ -Wall -fmessage-length=0 --std=c++11 -w -c -o Layer2d.o Layer2d.cpp
g++ -Wall -fmessage-length=0 --std=c++11 -w -c -o Neuron2dIterator.o Neuron2dIterator.cpp
g++ -Wall -fmessage-length=0 --std=c++11 -w -c -o input/2dinput/cross/cross.o input/2dinput/cross/cross.cpp
g++ -o bin/neural_net_2d Test2dSparselyNeuralNet.o NeuralNet.o Sparsely2dNeuralNetwork.o Connection.o Layer2d.o Neuron2dIterator.o input/2dinput/cross/cross.o
Layer2d.o: In function `Layer::Layer()':
Layer2d.cpp:(.text._ZN5LayerC2Ev[_ZN5LayerC5Ev]+0x13): undefined reference to `vtable for Layer'
Layer2d.o: In function `Iterator::Iterator()':
Layer2d.cpp:(.text._ZN8IteratorC2Ev[_ZN8IteratorC5Ev]+0xf): undefined reference to `vtable for Iterator'
Layer2d.o: In function `Layer::~Layer()':
Layer2d.cpp:(.text._ZN5LayerD2Ev[_ZN5LayerD5Ev]+0x13): undefined reference to `vtable for Layer'
Layer2d.o:(.rodata._ZTI7Layer2d[_ZTI7Layer2d]+0x10): undefined reference to `typeinfo for Layer'
Neuron2dIterator.o:(.rodata._ZTI16Neuron2dIterator[_ZTI16Neuron2dIterator]+0x10): undefined reference to `typeinfo for Iterator'
collect2: error: ld returned 1 exit status
make: *** [neural_net_2d] Error 1
makefile:
CXXFLAGS = -Wall -fmessage-length=0 --std=c++11 -w
CXXFLAGS_DEBUG = -g -Wall -fmessage-length=0 --std=c++11 -w
SAMPLES = input/2dinput/cross/cross.o
OBJS = Test2dSparselyNeuralNet.o NeuralNet.o Sparsely2dNeuralNetwork.o Connection.o Layer2d.o Neuron2dIterator.o ${SAMPLES}
LIBS =
TARGET = neural_net_2d
$(TARGET): $(OBJS)
$(CXX) -o bin/$(TARGET) $(OBJS) $(LIBS)
all: $(TARGET)
debug: $(OBJS)
$(CXX) -o bin/$(TARGET) $(OBJS) $(LIBS) $(CXXFLAGS_DEBUG)
clean:
rm -f $(OBJS) $(TARGET)
Layer.h
#ifndef LAYER_H
#define LAYER_H
#include "Neuron.h"
#include "Iterator.h"
class Layer
{
protected:
// biasNeuron
Neuron biasNeuron = 1.0;
public:
inline Layer() : biasNeuron(1.0) {}
virtual Iterator& start();
virtual Neuron& front(void);
virtual Neuron& back(void);
virtual int size();
protected:
private:
};
#endif // LAYER_H
Layer2d.h
#ifndef LAYER2D_H
#define LAYER2D_H
#include "Layer.h"
class Layer2d : public Layer
{
public: std::vector<std::vector<Neuron> > _neurons;
public:
Layer2d();
virtual ~Layer2d();
Iterator& start();
Neuron& front(void);
Neuron& back(void);
int size();
protected:
private:
};
#endif // 2DLAYER_H
Layer2d.cpp
#include "Layer2d.h"
#include "Neuron2dIterator.h"
class Neuron2dIterator;
Iterator& Layer2d::start(void)
{
Neuron2dIterator& it = (*new Neuron2dIterator(*this));
return it;
}
Neuron& Layer2d::front(void)
{
Neuron& frontNeuron = this->_neurons.front().front();
return frontNeuron;
}
Neuron& Layer2d::back(void)
{
Neuron& backNeuron = this->_neurons.back().back();
return backNeuron;
}
int Layer2d::size(void)
{
int size = this->_neurons.back().size() * this->_neurons.size();
return size;
}
Layer2d::Layer2d()
{
//ctor
}
Layer2d::~Layer2d()
{
//dtor
}
LineLayer.h
#ifndef LINELAYER_H
#define LINELAYER_H
#include "Layer.h"
#include "Neuron.h"
#include <vector>
using namespace std;
class LineIterator;
class LineLayer : public Layer
{
public: std::vector<Neuron> _neurons;
public:
LineLayer();
protected:
private:
};
#endif // LINELAYER_H
LineLayer.cpp
#include "LineLayer.h"
#include "LineIterator.h"
Iterator& LineLayer::start()
{
LineIterator& it = (*new LineIterator());
return it;
}
Neuron& LineLayer::front()
{
Neuron& frontNeuron = this->_neurons.front();
return frontNeuron;
}
Neuron& LineLayer::back()
{
Neuron& backNeuron = this->_neurons.back();
return backNeuron;
}
int LineLayer::size()
{
return this->_neurons.size();
}
LineLayer::LineLayer()
{
//ctor
}
LineLayer::~LineLayer()
{
//dtor
}
Thnx for help!

Answer 1

As explained at https://gcc.gnu.org/wiki/VerboseDiagnostics#missing_vtable the vtable will be in the same object file as the first non-inline virtual function, which is Layer::start. You haven't defined that function, so the compiler never generated the vtable.
To fix the linker error be sure you have provided a definition for the first non-inline virtual function declared in the class.