Different methods for instantiating an object in C++

Question

What is the difference between this:

Myclass *object = new Myclass();

and

Myclass object = new Myclass();

I have seen that a lot of C++ libraries like wxWidgets, OGRE etc use the first method... Why?

Answer 1

The second is wrong !

You may use

MyClass object;

That will work.

Now, concerning how to choose between these two possibilities, it mainly depends on how long your object should live. See there for a thorough answer.

Answer 2

The new operator returns a pointer to the object it creates, so the expression Myclass object = new Myclass(); is invalid.

Other languages don't have explicit pointers like C++ so you can write statements like Myclass object = new Myclass();, but in C++ this is simply not possible. The return type of new Myclass(); is a pointer to a Myclass object, i.e. Myclass *.

Answer 3

The first example creates a pointer to MyClass and initializes it to point to the result of the new operator.

The second will likely not compile, as it is trying to create a MyClass object and assign it to a MyClass pointer. This could work in the unlikely event that you have a MyClass constructor that accepts a MyClass pointer.

Answer 4

The first is correct.

The second will generally not compile. And if it does compile then the class is doing some complicated things in a constructor/assignment operator. And it's probably leaking memory.

Answer 5

Myclass *object = new Myclass(); //object is on the heap
Myclass object; //object is on the stack

You create objects on the heap if you plan on using them throughout a long period of time and you create objects on the stack for a short lifetime (or scope).