Simple Polymorphism cast not working - c++

Question

I have a class SourceComponent, and its derived class, PeriodicSourceComponent.
Implementations are:
class SourceComponent : public Component
{
protected:
friend class UserInterface;
friend void readInput();
public:
virtual int returnType();
virtual int propagateLogic();
virtual void sourcePropagation(float);
virtual void accept(VisitorSources&);
SourceComponent();
};
and
#include "source_component.h"
class PeriodicSourceComponent : public SourceComponent
{
private:
int frequency;
friend void main();
friend void readInput();
friend class UserInterface;
public:
void sourcePropagation(float);
int returnType();
PeriodicSourceComponent();
};
When I try in some different class/method to do:
SourceComponent* s = new PeriodicSourceComponent;
it won't let me, sayin "a value of type periodicblabla cant be assigned to value of type sourceblabla". Why?
Edit:
Ok, in my main it looks lke this:
#include "source_component.h"
#include "periodic_source_component.h"
void main()
{
SourceComponent* s = new PeriodicSourceComponent;
}
And implementations of both classes:
source.cpp:
#include "source_component.h"
SourceComponent::SourceComponent()
{
outputState = -1;
}
int SourceComponent::propagateLogic()
{
return 1;
}
int SourceComponent::returnType()
{
return 5;
}
and periodic.cpp
#include "periodic_source_component.h"
PeriodicSourceComponent::PeriodicSourceComponent()
{
outputState = 0;
}
int PeriodicSourceComponent::returnType()
{
return 3;
}
void PeriodicSourceComponent::sourcePropagation(float time)
{
float t = time, period;
period = 1000000/frequency;
if(t > period)
{
while(t >= period)
t -= period;
}
if(t <= (period/2))
outputState = 0;
else
outputState = 1;
}
and its not working... (outputState is a member of class Component, base class of SourceComponent)
and the error message: A value of type "PeriodicSourceComponent*" cannot be assigned to a value of type "SourceComponent*".
Important Edit
When I try to compile, the actual compiler error is at PeriodicSourceComponent declaration, it says: "Base class undefined".
and also, I have two other derived classes from SourceComponent, but I don't see how they could interfere with this one..
EDIT 4
Ok so I figured out what causes the error, you were right of course, it something else I didn't post. I have class VisitorSources, heres definition:
#ifndef __VISITOR_SOURCES_H__
#define __VISITOR_SOURCES_H__
#include "component.h"
#include "impulse_source_component.h"
#include "arbitrary_source_component.h"
#include "periodic_source_component.h"
class VisitorSources
{
protected:
VisitorSources();
public:
virtual void visitImpulseSource(ImpulseSourceComponent*);
virtual void visitArbitrarySource(ArbitrarySourceComponent*);
virtual void visitPeriodicSource(PeriodicSourceComponent*);
void visitSource(int, float);
};
#endif
And its implementation is not yet written:
#include "visitor_sources.h"
void visitSource(int type, float time)
{
}
void VisitorSources::visitArbitrarySource(ArbitrarySourceComponent* a)
{
}
When I comment out the entire Visitor class and implementation, the above-mentioned errors are gone for some reason. I have no idea why...
The only error that remains is that when I try to use s->frequency, it says that frequency is not a member of SourceComponent, which is true, but it is a member of PeriodicSourceComponent, which is why I used the cast in the first place..
Finally, here's the Component class, the main class for all almost all other classes in the project :P
#ifndef __COMPONENT_H__
#define __COMPONENT_H__
#include <iostream>
#include <vector>
class Component
{
friend class UserInterface;
friend void readAndSimulate();
protected:
Component();
int numOfInputs;
int numOfOutputs;
std::vector<Component*> inputs;
std::vector<Component*> outputs;
friend void main();
float lengthOfSimulation;
int typeIfSource;
public:
int outputState;
virtual int propagateLogic() = 0;
virtual int returnType();
int beginPropagation();
virtual void sourcePropagation(float);
~Component();
};
#endif
And implementation:
#include "component.h"
#include <conio.h>
Component::Component()
{
}
int Component::beginPropagation()
{
std::vector<Component*>::const_iterator iter = outputs.begin();
for(;iter<outputs.end();++iter)
{
if ((*iter)->outputState == -2)
{
(*iter)->outputState = outputState;
return (*iter)->outputState;
}
}
std::vector<Component*>::const_iterator it = outputs.begin();
int finishedCycle, x;
while(1)
{
finishedCycle = 1;
for(; it < outputs.end(); ++it)
{
x = (*it)->propagateLogic();
if(!x)
finishedCycle = 0;
}
if(finishedCycle) break;
it = outputs.begin();
}
it = outputs.begin();
for(;it<outputs.end();++it)
(*it)->beginPropagation();
}
int Component::returnType()
{
return 0;
}
void Component::sourcePropagation(float)
{
}
Component::~Component()
{
std::vector<Component*>::const_iterator it = inputs.begin();
for(; it < inputs.end(); ++it)
{
if((*it) != NULL)
{
delete *it;
Component* p = *it;
p = NULL;
}
}
it = outputs.begin();
for(; it < inputs.end(); ++it)
{
if((*it) != NULL)
{
delete *it;
Component* p = *it;
p = NULL;
}
}
}

Answer 1

Are you using include guards in all your header files?
Not having them can cause the kinds of problems you're seeing.

Answer 2

Three guesses:
You copied and pasted code between header files and forgot to change the #include guards.
You use precompiled headers and included something before the #include "stdafx.h".
If you use precompiled headers, try deleting the .pch file.