Segmentation fault when calling virtual function in C++

Question

I am currently working on an ECS in C++ for my game engine. I have a base system struct that has two virtual functions init() and update() which are implemented in derived structs. I have an addSystem() and removeSystem() functions which use templates and I have an array of System* systems. If I try to call them it gives me a segmentation fault.

System:

struct System{
public:
    uint32_t id;
    virtual void init(World* world){}
    virtual void update(World* world){}
};

addSystem():

template<typename T>
    void addSystem(){
        T* system = allocate<T>();
        system->id = getID();
        systems.append(system);
        #ifdef DEBUG
                LOG("ECS: System added successfully.");
        #endif // DEBUG
}

removeSystem():

template<typename T>
    void removeSystem(uint32_t id){
        unsigned int index;
        for(int i = 0; i < systems.size; i++){
            if (systems[i]->id == id){
                index = i;
                break;
            }
        }

        systems.remove(index);
}

Call to virtual function from System*:

for (int i = 0; i < systems.size; i++){
    systems[i]->init(this); // Here is the segmentation fault.
}

for (int i = 0; i < systems.size; i++){
    systems[i]->update(this); // Here is the segmentation fault.
}

Please ask if more info is needed.

Edit: size is equal to 1 in the for loop and systems[i] is a valid pointer. I also tested p systems[i]->update and it also has a valid address. The problem is while calling it.

Answer 1

#ifndef SYSTEMTEST_H_
#define SYSTEMTEST_H_

#include <stdint.h> 
#include <vector>
#include <iostream>

struct World
{
    int id;
};

struct System{
public:
    uint32_t id;
    virtual void init(World* world){}
    virtual void update(World* world){}
};

int systemID = 0;
std::vector<System*> systems;


struct Derived : System
{
    void init(World* world){
        std::cout << "init" << std::endl;
    }
    void update(World* world){
        std::cout << "update" << std::endl;
    }
};

uint32_t getID()
{
    return systemID++;
}

template<typename T> void addSystem(){
    T* system = new T();
    system->id = getID();
    //systems.append(system);
    systems.push_back(system);
}

template<typename T> void removeSystem(uint32_t id){
    unsigned int index;
    for (int i = 0; i < systems.size; i++){
        if (systems[i]->id == id){
            index = i;
            break;
        }
    }
    //remove operator
    //systems.remove(index);
}
#endif

#include <iostream>
#include "SystemTest.h"
using namespace std;

int main(int argc, char** argv){

    addSystem<Derived>();
    for (int i = 0; i < systems.size(); i++)
    {
        World *world;
        world = new World;
        systems[i]->init(world);
    }
    return 0;

}

I understand your description.

I try to complete the rest

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