[Turn]c++ new with parentheses and without parentheses

ref:http://m.blog.csdn.net/blog/u012745772/42420443

When the new object is added (), there is no (), do not know what is the difference?
Like what:
CBase *base = new cderived ();
CBase *base = new cdeviced;

Many people say that parentheses call a constructor without arguments, and no parentheses call a default constructor or a unique constructor. That's a problem.
For the custom class type:
If the class does not have a constructor defined (the default constructor is synthesized by the compiler) and there is no virtual function, then Class C = new class; The default constructor for the composition is not called, and Class C = new Class (); The default constructor is called. The requested space is initialized to 0
If the class does not have a constructor defined (the default constructor is synthesized by the compiler) but has a virtual function, then Class C = New class, and Class C = new Class (), and the default constructor is called. The requested space is not initialized to 0
If the class defines a default constructor, then Class C = New class, and Class C = new Class (), the default constructor is called.

For built-in types:
int *a = new int, the requested int space is not initialized, and int *a = new int (); The int space requested is initialized to 0.
The difference between the following two statements is that the value in the first dynamic request space is a random value, the second one is initialized, and the value is 0:
int *p1 = new INT[10];
int *p2 = new INT[10] ();
Conclusion: Do not use new without parentheses.
Class a{
Public
A () {a=1;}
Public
int A;
};
A *a1=new A;
A *a2=new a ();

cout<<a1->a<<endl; Output: 842150451
cout<<a2->a<<endl; Output 0
A A3;
cout<<a3.a<<endl; Run exception, A is not initialized.
If you add a virtual, such as virtual ~a () {},
The
cout<<a1->a<<endl; Output: 842150451
cout<<a2->a<<endl; Output-842150451

[Turn]c++ new with parentheses and without parentheses