C++ std::vector problems
- by Faur Ioan-Aurel
For 2 days i tried to explain myself some of the things that are happening in my c++ code,and i can't get a good explanation.I must say that i'm more a java programmer.Long time i used quite a bit the C language but i guess Java erased those skills and now i'm hitting a wall trying to port a few classes from java to c++.
So let's say that we have this 2 classes:
class ForwardNetwork {
protected:
ForwardLayer* inputLayer;
ForwardLayer* outputLayer;
vector<ForwardLayer* > layers;
public:
void ForwardNetwork::getLayers(std::vector< ForwardLayer* >& result ) {
for(int i= 0 ;i< layers.size(); i++){
ForwardLayer* lay = dynamic_cast<ForwardLayer*>(this->layers.at(i));
if(lay != NULL)
result.push_back(lay);
else cout << "Layer at#" << i << " is null" << endl;
}
}
void ForwardNetwork::addLayer ( ForwardLayer* layer ) {
if(layer != NULL)
cout << "Before push layer is not null" << endl;
//setup the forward and back pointer
if ( this->outputLayer != NULL ) {
layer->setPrevious ( this->outputLayer );
this->outputLayer->setNext ( layer );
}
//update the input layer and outputLayer variables
if ( this->layers.size() == 0 )
this->inputLayer = this->outputLayer = layer;
else this->outputLayer = layer;
//push layer in vector
this->layers.push_back ( layer );
for(int i = 0; i< layers.size();i++)
if(layers[i] != NULL)
cout << "Check::Layer[" << i << "] is not null!" << endl;
}
};
Second class:
class Backpropagation : public Train {
public:
Backpropagation::Backpropagation ( FeedForwardNetwork* network ){
this->network = network;
vector<FeedforwardLayer*> vec;
network->getLayers(vec);
}
};
Now if i add from main() some layers into network via addLayer(..) method it's all good.My vector is just as it should.But after i call Backpropagation() constructor with a network object ,when i enter getLayers(), some of my objects from vector have their address set to NULL(they are randomly chosen:for example if i run my app once with 3 layer's into vector ,the first object from vector is null.If i run it second time first 2 objects are null,third time just first object null and so on).
Now i can't explain why this is happening.I must say that all the objects that should be in vector they also live inside the network and they are not NULL;
This happens everywhere after i done with addLayer() so not just in the getLayers().
I cant get a good grasp to this problem.I thought first that i might modify my vector.But i can't find such thing.
Also why if the reference from vector is NULL ,the reference that lives inside ForwardNetwork as a linked list (inputLayer and outputLayer) is not NULL?
I must ask for your help.Please ,if you have some advices don't hesitate!
PS: as compiler i use g++ part of gcc 4.6.1 under ubuntu 11.10
