问题
Isn't
A a = new A(); // A is a class name
supposed to work in C++?
I am getting:
conversion from 'A*' to non-scalar type 'A' requested
Whats wrong with that line of code?
This works in Java, right?
Also, what is the correct way to create a new object of type A in C++, then?
回答1:
No, it isn't. The new operation returns a pointer to the newly created object, so you need:
A * a = new A();
You will also need to manage the deletion of the object somewhere else in your code:
delete a;
However, unlike Java, there is normally no need to create objects dynamically in C++, and whenever possible you should avoid doing so. Instead of the above, you could simply say:
A a;
and the compiler will manage the object lifetime for you.
This is extremely basic stuff. Which C++ text book are you using which doesn't cover it?
回答2:
new A() returns a pointer A*. You can write
A a = A();
which creates a temporary instance with the default constructor and then calls the copy constructor for a or even better:
A a;
which just creates a with the default constructor. Or, if you want a pointer, you can write
A* a = new A();
which allows you more flexibility but more responsibility.
回答3:
The keyword new is used when you want to instantiate a pointer to an object:
A* a = new A();
It gets allocated onto the heap.. while when you don't have a pointer but just a real object you use simply
A a;
This declares the object and instantiate it onto the stack (so it will be alive just inside the call)
回答4:
You need A* a= new A();
new A(); creates and constructs an object of type A and puts it on the heap. It returns a pointer of that type.
In other words new returns the address of where the object was put on the heap, and A* is a type that holds an address for an object of type A
Anytime you use the heap with new you need to call an associated delete on the address.
回答5:
new gets you a pointer to the created object, therefore:
A *a = new A();
回答6:
First, new returns a pointer, so you need to declare the a's type as 'A*'. Second, unlike Java, you don't need parenthesis after A:
A* a = new A;
来源：https://stackoverflow.com/questions/2647660/creation-of-an-object-in-c