return types [RESOLVED]

Object Object::Foo(); vs Object& Object:Foo()

What is the difference between returning and object and returning a reference to the object? If there is a difference, when would you use each case?

The first returns a copy of a local object, the second returns a reference to a (possibly) local object. You should never return a reference to a local object, since it will fall out of scope at the end of the function and you'll have a reference to a destroyed object. You can return a reference when you are returning something that will not die in the scope of the function.

Here's an example of when you CAN return a reference:

Code:

---

class Object
{
    private:
        // store Object pointers to delete them later.
        vector<Object*> myObjects;
    public:
        Object& Foo()
        {
          Object* o = new Object();
          myObjects.push_back(o);
       
          // since this was allocated with new,
          // it will live past the end of this function
          // until the Object that created it goes out of scope
          // and the constructor below is called.
          return (*o);
        }

        ~Object()
        {
                while(myObjects.size() != 0)
                {
                        delete myObjects.back();
                        myObjects.pop_back();
                }
        }

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It's common to return references in member operators, like;

Code:

---

class BigInt
{
public:
    // assign *this = b; return (*this);
    BigInt& operator=(const BigInt& b);
    // assign *this = *this + b; return (*this);
    BigInt& operator+=(const BigInt& b);
    // assign *this = *this - b; return (*this);
    BigInt& operator-=(const BigInt& b);
}

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so that you can do something like

Code:

---

BigInt a, b, c;
a = b = c; // (b = c) returns a reference to b, so that a = b.

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thanks for clearing that up :)