Question

Consider the following class.

class mapping_items
{
public:

    mapping_items(){}

    void add(const mapping_item* item) {
        items_.push_back( item );
    }

    size_t count() const{
        return items_.size();
    }

    const mapping_item& find(const std::string& pattern){
        const mapping_item* item = // iterate vector and find item;
        return *item; 
    }

private:
    mapping_items(const mapping_items&); // not allowed
    mapping_items& operator=(const mapping_items&); // not allowed
    std::vector<const mapping_item*> items_;
};

C++ FAQ says,

Use references when you can, and
pointers when you have to.

So in the above example, should I return const mapping_item& or const mapping_item* ?

The reason why I chose mapping_item& is because there will be always a default return value available. I will never have null returns. So a reference makes it clear that it can’t have nulls. Is this the correct design?

Answer 1

There is a problem – what happens if your find() function fails? If this is expected never to happen, you are OK returning a reference (and raise an exception if it happens despite the fact it shouldn’t). If on the other hand it may happen (e.g. looking up a name in an address book), you should consider returning a pointer, as a pointer can be NULL, indicating the find failed.