How to return a class object by reference in C++?

42

I have a class called Object which stores some data.

I would like to return it by reference using a function like this:

    Object& return_Object();

Then, in my code, I would call it like this:

    Object myObject = return_Object();

I have written code like this and it compiles. However, when I run the code, I consistently get a seg fault. What is the proper way to return a class object by reference?

This question is tagged with c++ reference segmentation-fault return-by-reference

~ Asked on 2012-01-18 17:27:07

The Best Answer is


55

You're probably returning an object that's on the stack. That is, return_Object() probably looks like this:

Object& return_Object()
{
    Object object_to_return;
    // ... do stuff ...

    return object_to_return;
}

If this is what you're doing, you're out of luck - object_to_return has gone out of scope and been destructed at the end of return_Object, so myObject refers to a non-existent object. You either need to return by value, or return an Object declared in a wider scope or newed onto the heap.

~ Answered on 2012-01-18 17:30:44


22

You can only use

     Object& return_Object();

if the object returned has a greater scope than the function. For example, you can use it if you have a class where it is encapsulated. If you create an object in your function, use pointers. If you want to modify an existing object, pass it as an argument.

  class  MyClass{
      private:
        Object myObj;

      public:
         Object& return_Object() {
            return myObj;
         }

         Object* return_created_Object() {
            return new Object();
         }

         bool modify_Object( Object& obj) {
            //  obj = myObj; return true; both possible
            return obj.modifySomething() == true;
         }
   };

~ Answered on 2012-01-18 17:40:07


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