Different methods for instantiating an object in C++

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?

Solution 1:

Myclass *object = new Myclass(); //object has dynamic storage duration (usually is on the heap)
Myclass object; //object has automatic storage duration (usually is on the stack)

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

Solution 2:

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.

Solution 3:

Your first line is 100% correct. Unfortunately, you can't create object with your second line in c++. There are two ways to make/create an object in c++.

First one is :

MyClass myclass; // if you only need to call the default constructor    
MyClass myclass(12); // if you need to call constructor with parameters*

Second one is :

MyClass *myclass = new MyClass();// if you only need to call the default constructor
MyClass *myclass = new MyClass(12);// if you need to call constructor with parameters

In c++ if you use the new keyword, object will be stored in heap. It's very useful if you are using this object for a long time period and if you use first method, it will be stored in stack. it can be used only short time period. Notice: if you use new keyword, remember it will return pointer value. You should declare name with *. If you use second method, it doesn't delete object in the heap. You must delete by yourself using delete keyword:

delete myclass;