CG bug in VC7.1?

[Hendrik Schober]

Hi,

consider this:

#include <iostream>

struct Base {
Base() {std::cout << "Base\n";}
Base(Base&) {std::cout << "Base(Base&)\n";}
};

template< typename T >
struct TBase : Base {
TBase() : Base() {};
TBase(Base& obj) : Base(obj) {std::cout << "TBase(Base&)\n";}
};

struct Derived : TBase<int> {
Derived() : TBase<int>() {std::cout << "Derived()\n";}
Derived(Derived& obj) : TBase<int>(obj) {std::cout << "Derived(Derived&)\n";}
};
int main()
{
Derived d1;
Derived d2(d1);
return 0;
}

(Of course, this doesn' make sense. The real code
is a lot more complicated.)
Using VC7.1 this outputs

Base
TBase()
Derived()
Base(Base&)
Derived(Derived&)

whereas I would have expected

Base
TBase()
Derived()
Base(Base&)
TBase(Base&)
Derived(Derived&)

Am I missing something or is the compiler wrong?

Schobi

--
Sp******@gmx.de is never read
I'm Schobi at suespammers dot org

"The presence of those seeking the truth is infinitely
to be prefered to those thinking they've found it."
Terry Pratchett

[Carl Daniel [VC++ MVP]]

Hendrik Schober wrote:

Hi,
[snipped]
Am I missing something or is the compiler wrong?

I'd say the compiler's wrong. Does using const references in the
constructor argument lists make any difference? Have you tried VC++ 2005?
Do optimizationg settings make any difference?

-cd

[Ioannis Vranos]

Hendrik Schober wrote:

(Of course, this doesn' make sense. The real code
is a lot more complicated.)
Using VC7.1 this outputs

Base
TBase()
Derived()
Base(Base&)
Derived(Derived&)

whereas I would have expected

Base
TBase()
Derived()
Base(Base&)
TBase(Base&)
Derived(Derived&)

Actually it outputs
C:\c>temp
Base
Derived()
Base(Base&)
Derived(Derived&)

C:\c>

At first I want to note that you use some unneeded explicit calls to
base constructors.
I will mark what is called with numbers for the first object, just
follow the numbers from the largest to the smaller:
#include <iostream>

struct Base {
==>1 Base() {std::cout << "Base\n";}
Base(Base&) {std::cout << "Base(Base&)\n";}
};

template< typename T >
struct TBase : Base {
==>2 TBase() : Base() {};
TBase(Base& obj) : Base(obj) {std::cout << "TBase(Base&)\n";}
};

struct Derived : TBase<int> {
==>3 Derived() : TBase<int>() {std::cout <<
"Derived()\n";}

Derived(Derived& obj) : TBase<int>(obj) {std::cout <<
"Derived(Derived&)\n";}
};
int main()
{
Derived d1;
}


--
Ioannis Vranos

[Tom Widmer]

Hendrik Schober wrote:

Hi,

consider this:

#include <iostream>

struct Base {
Base() {std::cout << "Base\n";}
Base(Base&) {std::cout << "Base(Base&)\n";}
};

template< typename T >
struct TBase : Base {
TBase() : Base() {};
TBase(Base& obj) : Base(obj) {std::cout << "TBase(Base&)\n";}
};

struct Derived : TBase<int> {
Derived() : TBase<int>() {std::cout << "Derived()\n";}
Derived(Derived& obj) : TBase<int>(obj) {std::cout << "Derived(Derived&)\n";}
TBase<int>(obj) calls TBase<int>(TBase&) (the implicitly defined copy
constructor), not TBase<int>(Base&) as you are expecting -
Derived->TBase<int> is a better conversion than Derived->Base.
};
int main()
{
Derived d1;
Derived d2(d1);
return 0;
}

(Of course, this doesn' make sense. The real code
is a lot more complicated.)
Using VC7.1 this outputs

Base
TBase()
Derived()
Base(Base&)
Derived(Derived&)

whereas I would have expected

Base
TBase()
Derived()
Base(Base&)
TBase(Base&)
Derived(Derived&)

Am I missing something or is the compiler wrong?

I think it's right.

Tom

[Hendrik Schober]

Ioannis Vranos <iv*@remove.this.grad.com> wrote:

[...]

Using VC7.1 this outputs

Base
TBase()
Derived()
Base(Base&)
Derived(Derived&)
[...]

Actually it outputs
C:\c>temp
Base
Derived()
Base(Base&)
Derived(Derived&)

You're right. Sorry for this stupid
copy'n'paste error.
At first I want to note that you use some unneeded explicit calls to
base constructors.
This was code to show the problem.
The real code is much more messy. I
just reduced it to what I posted and
didn't go through looking for this.
[...]

Schobi

--
Sp******@gmx.de is never read
I'm Schobi at suespammers dot org

"The presence of those seeking the truth is infinitely
to be prefered to those thinking they've found it."
Terry Pratchett

[Hendrik Schober]

Tom Widmer <to********@hotmail.com> wrote:

Hendrik Schober wrote:

Hi,

consider this:

#include <iostream>

struct Base {
Base() {std::cout << "Base\n";}
Base(Base&) {std::cout << "Base(Base&)\n";}
};

template< typename T >
struct TBase : Base {
TBase() : Base() {};
TBase(Base& obj) : Base(obj) {std::cout << "TBase(Base&)\n";}
};

struct Derived : TBase<int> {
Derived() : TBase<int>() {std::cout << "Derived()\n";}
Derived(Derived& obj) : TBase<int>(obj) {std::cout << "Derived(Derived&)\n";}
TBase<int>(obj) calls TBase<int>(TBase&) (the implicitly defined copy
constructor), not TBase<int>(Base&) as you are expecting -
Derived->TBase<int> is a better conversion than Derived->Base.

You're right!
Inserting 'TBase::TBase(TBase& obj)' shows that
this indeed is called.
I didn't know that a ctor taking a non-const
reference would be considered a copy ctor --
let alone that the compiler would generate
such a beast when it is needed! But Comeau
accepts it, so it really seems right. (Not
that I would questions your judgements! <g>)
[...]

Am I missing something or is the compiler wrong?
I think it's right.

Thanks!
Tom

Schobi

--
Sp******@gmx.de is never read
I'm Schobi at suespammers dot org

"The presence of those seeking the truth is infinitely
to be prefered to those thinking they've found it."
Terry Pratchett

[Hendrik Schober]

Carl Daniel [VC++ MVP] <cp*****************************@mvps.org.nospam > wrote:

Hendrik Schober wrote:

Hi,
[snipped]

Am I missing something or is the compiler wrong?

[...] Does using const references in the
constructor argument lists make any difference? [...]

I think it did. However, a non-const
ref is needed there.
(But I think Tom explained what was
wrong with the code -- or rather with
my expectations of what it should do!)
-cd

Schobi

--
Sp******@gmx.de is never read
I'm Schobi at suespammers dot org

"The presence of those seeking the truth is infinitely
to be prefered to those thinking they've found it."
Terry Pratchett