question about constructor

[July]

consider the following code:
#include <iostream>
using namespace std;
class A {
public:
A() {
cout << 'A';
}
};
class B {
public:
B() {
cout << 'B';
}
private:
A a;
};
int main()
{
B b;
}

Why the output is AB not BA ?
And when the A::A() be called ?

[John Carson]

"July" <ju**********@yahoo.com> wrote in message
news:11*********************@o13g2000cwo.googlegro ups.com

consider the following code:
#include <iostream>
using namespace std;
class A {
public:
A() {
cout << 'A';
}
};
class B {
public:
B() {
cout << 'B';
}
private:
A a;
};
int main()
{
B b;
}

Why the output is AB not BA ?
And when the A::A() be called ?

The order of construction is:

1. base object constructor.
2. member object constructor.
3. body of own constructor function.
--
John Carson

[Xie Yubo]

July wrote:

consider the following code:
#include <iostream>
using namespace std;
class A {
public:
A() {
cout << 'A';
}
};
class B {
public:
B() {
cout << 'B';
}
private:
A a;
};
int main()
{
B b;
}

Why the output is AB not BA ?
And when the A::A() be called ?

Obviously, the member object of the class is first constructed.

--
Best Regards

Xie Yubo
Email: xi*****@gmail.com Website: http://xieyubo.cn/
Harbin Institute of Technology
Phone: [phone] Fax: [phone]

[Ken Wilson]

On 17 Jul 2005 06:22:43 -0700, "July" <ju**********@yahoo.com> did
courageously avow:

consider the following code:
#include <iostream>
using namespace std;
class A {
public:
A() {
cout << 'A';
}
};
class B {
public:
B() {
cout << 'B';
}
private:
A a;
};
int main()
{
B b;
}

Why the output is AB not BA ?
And when the A::A() be called ?

Because the base class is called first, and then any derived classes,
in order?
Ken Wilson
"Coding, coding, over the bounding main()"

[Peter Julian]

"July" <ju**********@yahoo.com> wrote in message
news:11*********************@o13g2000cwo.googlegro ups.com...

consider the following code:
#include <iostream>
using namespace std;
class A {
public:
A() {
cout << 'A';
}
};
class B {
public:
B() {
cout << 'B';
}
private:
A a;
};
int main()
{
B b;
}

Why the output is AB not BA ?
And when the A::A() be called ?

Because you need to build the engine *before* you can start building the
car. The same goes with any other component in such a "composition".