Question

I’m quite new to C++ and I am trying to store objects inside a std::vector like this:

Event.h:

//event.h
class Event
{
public:
    Event();
    Event(std::string name);
    ~Event();
    void addVisitor(Visitor visitor);

private:
    std::vector<Visitor> m_visitors;

};

Event.cpp:

//event.cpp
Event::Event() :
    m_name("Unnamed Event")
{

}
Event::Event(std::string name) :
    m_name(name)
{

}
void Event::addVisitor(Visitor visitor)
{
    this->m_visitors.push_back(visitor);
}
void Event::listVisitors()
{
    std::vector<Visitor>::iterator it;
    for(it = this->m_visitors.begin();it != this->m_visitors.end(); ++it)
    {
        std::cout << it->getName() << std::endl;
    }
}

Visitor.h:

//visitor.h
class Visitor
{
    public:
    Visitor();
    Visitor(std::string name);
    ~Visitor();
    std::string getName() const;
    void listVisitors();

    private:
    std::string m_name;
};

Visitor.cpp:

//visitor.cpp
Visitor::Visitor() :
    m_name("John Doe")
{

}
Visitor::Visitor(std::string name) :
    m_name(name)
{

}
std::string Visitor::getName() const
{
    return m_name;
}

main.cpp:

//main.cpp
int main()
{
    Event *e1 = new Event("Whatever");
    Visitor *v1 = new Visitor("Dummy1");
    Visitor *v2 = new Visitor("Dummy2");

    e1->addVisitor(*v1);
    e1->addVisitor(*v2);
}

If I do it like this I would have to add a copy constructor which would make a deep copy so the object gets copied properly into the vector. I’m looking for a way around it by only storing pointers to the objects in a vector.
I already tried it with std::vector<std::unique_ptr<Visitor> > m_visitors, but then I got some errors when calling addVisitor in main.cpp. Of course I changed the declaration of the class members accordingly.
How would an appropriate declaration of the members and the member function look like to make it work?

Answer 1

Stylistically, if you are passing pointers, just accept pointers as the function arguments.

What’s happening in the example code above is that the visitors are getting copied to become function arguments and the pointers you had are unreferenced by anything outside of the main function.

I can’t speak to what the errors are that you’re seeing as you didn’t describe them but it probably has to do with incompatible types.

Just get rid of the news because for these data structures they’re unnecessary.

int main()
{
    Event e1("Whatever");
    Visitor v1("Dummy1");
    Visitor v2("Dummy2");

    e1.addVisitor(v1);
    e1.addVisitor(v2);
}

I would suggest that if you don’t know how to use pointers you couldn’t possibly want to store them instead (they’re a hassle IMO to store in the vector when copying by value works just fine).

The compiler generated copy constructor should work just fine.