Trying to implement Observer Patterns and got Segmentation Fault (pls help) c++ - gcc

Question

I'm trying to learn c++ so, I try to implement the observer patterns from the book Game Progamming Patterns but I'm always getting Segmentation Fault.
Searching arround I saw that Segmentation fault happens when a program try to access a non allocated memory. So I tried hard to fix it, but I can't. Someone can help me?
Here is my code:
Observer.h
#ifndef OBSERVER_H
#define OBSERVER_H
#include "EntityAndEvent.h"
#include "Subjects.h"
class Observer
{
private:
Observer* next_;
public:
Observer()
: next_(nullptr)
{}
virtual void onNotify(const Entity& entity, Event::Type event) = 0;
// Other stuff...
friend class Subjects;
};
#endif
Achievements.cpp
#ifndef ACHIEVEMENTS_CPP
#define ACHIEVEMENTS_CPP
#include "Observer.h"
#include <vector>
class Achievements : public Observer
{
public:
enum Type{
FELL_OFF,
AWAKE_ON
};
private:
std::vector<Type> done{};
public:
virtual void onNotify(const Entity&, Event::Type);
void unlock(Achievements::Type);
void printDone();
};
void Achievements::onNotify(const Entity& entity, const Event::Type event)
{
switch (event)
{
case Event::Type::ENTITY_FELL:
if(entity.isHero())
unlock(Achievements::Type::FELL_OFF);
break;
case Event::Type::ENTITY_AWAKE:
if(entity.isHero())
unlock(Achievements::Type::AWAKE_ON);
break;
default:
break;
}
};
void Achievements::unlock(Achievements::Type achiev)
{
done.push_back(achiev);
}
void Achievements::printDone()
{
// assert(done.size());
for(size_t i{0}; i < done.size(); i++)
{
std::cout << done[i] << "\n";
}
};
EntityAndEvent.cpp (i create this just to work with observer and subjects)
#ifndef ENTITY_AND_EVENT_H
#define ENTITY_AND_EVENT_H
class Entity
{
public:
inline const bool isHero() const {return true;}
};
class Event
{
public:
enum Type{
ENTITY_FELL,
ENTITY_AWAKE
};
};
#endif
Subjects.h
#ifndef SUBJECT_H
#define SUBJECT_H
#include "Observer.h"
#include <vector>
class Observer;
class Subjects
{
private:
// when implements this, prefer to use linked list or another optimized algorithms
Observer* head_{};
protected:
void notify(const Entity& Entity, Event::Type event);
public:
Subjects() : head_(NULL)
{};
~Subjects() {}
void addObserver(Observer* observer);
// const int getNumObs() const {return num_obs_;}
};
#endif
Subjects.cpp
#include "Subjects.h"
#include <cassert>
void Subjects::notify(const Entity& entity, Event::Type event)
{
Observer* observer = head_;
while (observer != NULL)
{
observer->onNotify(entity, event);
observer = observer->next_;
};
};
void Subjects::addObserver(Observer* observer)
{
if (head_ != nullptr)
observer->next_ = head_;
head_ = observer;
};
Physics.cpp (i create this just to populates the subject)
#ifndef PHYSICS_H
#define PHYSICS_H
#include "Subjects.h"
#include "EntityAndEvent.h"
class Physics: public Subjects
{
private:
public:
void update(const Entity& entity)
{
if (entity.isHero())
{
notify(entity, Event::Type::ENTITY_AWAKE);
};
};
};
#endif
main.cpp
#include "Observer.h"
#include "Achievements.h"
#include "Achievements.cpp"
#include "EntityAndEvent.h"
#include "Physics.h"
#include "Subjects.h"
#include "Subjects.cpp"
int main()
{
Physics *p{};
Entity e{};
Achievements *achiev{};
p->addObserver(achiev);
p->update(e);
return 0;
}

Answer 1

With Physics *p{}; you are declaring a pointer, but it currently does not point to a valid object (it is being initialized as nullptr here). Therefore, calling p->addObserver results in a segmentation fault. You should be able to confirm this by running the program in a debugger.
Why are you using a pointer here? Change Physics *p{}; to Physics p{};.
Disclaimer: Since your code is definitely not a minimum example I didn't look into the whole code or even tried to compile it. I'm only posting an answer because there is a clear error in the main function (use of an invalid pointer) that results in a segmentation fault.

Answer 2

first, tks for the reply. #darcamo that works. I dont know why it was declared as pointer.
I fixed that, so if anyone else have the same doubt check below:
main.cpp
#include "Observer.h"
#include "Achievements.h"
#include "EntityAndEvent.h"
#include "Physics.h"
#include "Subjects.h"
int main()
{
Physics p{};
Entity e{};
Achievements achiev{};
Observer* ptr_achiev{&achiev};
p.addObserver(ptr_achiev);
p.update(e);
return 0;
}