Netbeans在c ++中创建了一个默认构造函数。 它有什么作用？

Question

Netbeans created this default constructor. I was curious what is its purpose. I don't know what to call it, or what it does. It more of a curiosity. My only thought was maybe cloning? something tells me I am wrong.

#ifndef     FOO_H
#define FOO_H

class Foo {
public:
    Foo();
    Foo(const Foo& orig);
    virtual ~Foo();
private:

};

Answer 1

Yes Netbeans has kindly created explicitly created the default and copy constructors.

It has also supplied you a virtual destructor to help you avoid memory leaks when inheriting from this class (Consider BabyFoo to be a child class of Foo): if you write Foo* foo = new BabyFoo(); delete foo; Foo* foo = new BabyFoo(); delete foo; then you'll leak memory as the member data in BabyFoo will not be deleted unless Foo has a virtual destructor.

I don't like the way Netbeans does this because:

1) I think that a copy constructor can be difficult to maintain (it's easy to forget to copy a newly added member datum) and is unnecessary to supply if your member data don't need to be explicitly copied (bare pointer data would probably need to be explicitly copied). The one automatically generated by the compiler will (shallow) copy all member data.

2) A virtual destructor introduces a virtual function pointer table into your class which is an overhead.

3) Acknowledge Oli Charlesworth's comment: http://en.wikipedia.org/wiki/Rule_of_three_(C%2B%2B_programming)

Answer 2

Foo(const Foo& orig); 

This is copy constructor, every class has aa default copy constructor which is provided by the compiler

there purpose is to create a copy of an existing object

Refer http://en.wikipedia.org/wiki/Copy_constructor for more details about copy constructor