Returning a pointer to a class within a class

Question

this is the first time I've done something like this so I'm a little uncertain how I need to do this. I have a very simple class which contains some simple values and some getters:

class Nucleotide{
    private:
        char Base;
        int Position;
        int Polymorphic;
    public:
        Nucleotide(char ch, int pos);
        int getPos();
        char getBase();
        int getPoly();
};

This class is present in another class that contains a vector of them:

class NucleotideSequence{
    private:
        std::string Name;
        std::vector<Nucleotide> Sequence;
    public:
        NucleotideSequence(std::string name, std::vector<Nucleotide> seq);
        std::string getName();
        Nucleotide getBase(int pos1);
};

I want the method of the second class called getBase to be able to take a integer - say 1, and return the first Nucleotide object in the vector. What I've written is below:

Nucleotide NucleotideSequence::getBase(int pos1)
{
    for(std::vector<Nucleotide>::iterator i = Sequence.begin(); i != Sequence.end(); i++)
    {
        if(pos1 == (*i).getPos())
        {
            return i; // Return a pointer to the correct base.
        }
    }
}

I've got Nucleotide as the return type but I was wondering really how I should change this - since if I return nucleotide because of pass by value would it not just return a copy of the object at that place in the vector? So I'd rather return a pointer/reference. I'm using an iterator in the loop so should I just return a pointer with the value of the iterator? How do I do this? In the function I return i but should I be returning i&? I'm uncertain about the specifics - presumably if I'm returning a pointer my return type needs to be Nucleotide* or perhaps Nucleotide& since & means address of? I've thought this through and read Cpp tuts but I'm still slightly unsure of the right answer.

Thanks, Ben.

Answer 1

You have to return the Nucleotide by reference:

Nucleotide & NucleotideSequence::getBase(int pos1)
{
    for(std::vector<Nucleotide>::iterator i = Sequence.begin(); i != Sequence.end(); i++)
    {
        if(pos1 == (*i).getPos())
        {
            return *i; // Notice the *i instead of i
        }
    }
}

A reference works very similarly to pointer (allows you to pass the actual object, not its copy), but cannot be null and cannot point to non-existing object, so it's a lot safer than pointer.

Note though, that if you don't find the desired Nucleotide, you don't return anything, what generally is not a good idea. In this case using pointers may actually be a better idea:

Nucleotide * NucleotideSequence::getBase(int pos1)
{
    for(std::vector<Nucleotide>::iterator i = Sequence.begin(); i != Sequence.end(); i++)
    {
        if(pos1 == (*i).getPos())
        {
            return &(*i); 
        }
    }

    return nullptr;
}