can anybody help me out

[Cedric Moonen]

No, really, it's true...

Cédric Moonen Software developer
Charting control [v1.2]

[CPallini]

Iain Clarke wrote:

2/ Less trivially, the first example just calls the constructor. The second example makes two objects, (obj, and a temp one), then copies temp to obj, then destroys the temp object.

I thought the same. But I made a little test (optimization disabled):

#include using namespace std;

class MyClass
{
public:
int _a, _b;
MyClass(){}
MyClass(int a, int b):_a(a), _b(b){}
// copy constructor and assignment operator arbitrarly messed up.
MyClass(const MyClass & proto)
{
_a = 0;
_b = 0;
}
MyClass & operator = (const MyClass & proto)
{
_a = proto._b;
_b = proto._a;
return *this;
}
};

void main()
{
MyClass my1(3,2);
MyClass my2=MyClass(3,2);

MyClass my3(my1);
MyClass my4;
my4=my1;

cout << "my1: " << my1.\_a << " " << my1.\_b << endl;
cout << "my2: " << my2.\_a << " " << my2.\_b << endl;
cout << "my3: " << my3.\_a << " " << my3.\_b << endl;
cout << "my4: " << my4.\_a << " " << my4.\_b << endl;

}

and to my surprise, the output:

my1: 3 2
my2: 3 2
my3: 0 0
my4: 2 3

Well I'm really upset about. What do you think?

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
[my articles]

[Cedric Moonen]

It's because the compiler will treat this:

CMyCLass my1 = my2;

As this:

CMyClass my1(my2);

If you would have done that operation on two lines, then the assignment operator would have been called.

Cédric Moonen Software developer
Charting control [v1.2]

[Iain Clarke Warrior Programmer]

CPallini wrote:

What do you think?

Well, I immediately quibbled your tests, so I did some of my own...

class MyClass
{
public:
int _a, _b;
MyClass()
{
TRACE0("Blank Constructor\n");
}
~MyClass()
{
TRACE0("Destructor\n");
}
MyClass(int a, int b):_a(a), _b(b)
{
TRACE2("Parameter Constructor(%i,%i)\n", a,b);
}
// copy constructor and assignment operator arbitrarly messed up.
MyClass(const MyClass & proto)
{
_a = 0;
_b = 0;
TRACE0("Copy Constructor\n");
}
MyClass & operator = (const MyClass & proto)
{
_a = proto._b;
_b = proto._a;
TRACE0("Copying\n");
return *this;
}
};

void main()
{
MyClass my1(3,2);
MyClass my2=MyClass(30,20);
}

And I got:

Parameter Constructor(3,2)
Parameter Constructor(30,20)

which came as a suprise. So, the second case is being "Optimised" - even with no compiler optimisation. So C++ is treating the two cases as grammatically equivalent. This is why I help here - I learn something by code-spelunking too! Iain.

[CPallini]

Cedric Moonen wrote:

I don't need any assistance

Sure? :laugh:

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
[my articles]

[CPallini]

Nope, the compiler treats

MyClass my2 = MyClass(3,2);

as it was

MyClass my2(3,2);

(I've messed up both copy constructor and assignment operator to detect it) and IMHO skipping the temporary object construction and the assignment operator is really weird, but I don't know what the C++ standard requires. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
[my articles]

[Iain Clarke Warrior Programmer]

I knew *someone* would bite - but I assumed it would be Signor Pallini. And he's the one who gave a sensible reply! Iain.

[CPallini]

Now you have to fix all that database and network stuff! :laugh:

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
[my articles]

[CPallini]

Iain Clarke wrote:

I knew *someone* would bite

WOW I missed something, anyway usually Cedric is a very nice guy.

Iain Clarke wrote:

but I assumed it would be Signor Pallini

Pallini is a quite docile guy too, isn't he? BTW Signor in that context was fantastic!

Iain Clarke wrote:

And he's the one who gave a sensible reply!

Oh, well, hence I can assume he is. :-D

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
[my articles]

[Cedric Moonen]

Well, it's friday :rolleyes: That explains a lot :-D

Cédric Moonen Software developer
Charting control [v1.2]