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Hi,
Could anybody explain why in QueryInterface()we use static_cast for casting pointers to interfaces to be returned by the functions, but inside the function in order to call AddRef() we call reintepret_cast like this:
reinterpret_cast<iunknown*>(*ppv)->AddRef();?
Why not just using static_cast as well?
Any input would be of great value and much appreciated.
Thanks.
skruss
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if you find these words like static_cast,reintepret_cast and dynamic_cast
on msdn you will find the answer.
nice to meet u
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Thanks very much. I looked their and found it very helpful indeed.
Nice to meet you too.
skruss
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skruss wrote:
Why not just using static_cast as well?
It's a matter of taste really. They exist so that you can tell the compiler what it is that you want to accomplish. That way, the compiler can issue warnings/errors if what you want to do is illegal.
Of course, dynamic_cast is slightly different from the other casting operators in that it actually does the cast in runtime (it returns 0 if A is not assignable to B - B* b = dynamic_cast<A*>
reinterpret_cast should be avoided unless you really need it. Why? Because it basically tells the compiler to cast whatever into whatever. The compiler can thus not issue any warnings/errors.
--
Booohoo!
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hi, i want to learn COM from vb. does anyone know any usefull document that teach COM or COM+ from the beginner. some document that i had could not make the beginner like me to understand. please provide me any tips or trick to solve that problem. 
Roath Kanel
APO-CEDC
Save Children Norway-Cambodia Office
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I'm trying to use the conversion macros (OLE2A, OLE2CA, etc) and I know I need to add the USES_CONVERSION macro, but where do I put it? I put it in my header file and I keep getting compiler errors that a bunch of the variables it declares are missing their type-specifiers and such. Am I doing something wrong? Thanks.
Also, this is off topic from the subject, but is there anything like CString for ATL?
- Aaron
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Aaron,
In answer to the question of CString functionality for ATL, try looking at this (http://www.codeguru.com/Cpp/COM-Tech/atl/atl/article.php/c67/) I've used this in the past and worked a treat 
- Andy
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monrobot13 wrote:
I'm trying to use the conversion macros (OLE2A, OLE2CA, etc) and I know I need to add the USES_CONVERSION macro, but where do I put it? I put it in my header file and I keep getting compiler errors that a bunch of the variables it declares are missing their type-specifiers and such. Am I doing something wrong? Thanks.
You place the USES_CONVERSION macro inside every function definition that will use conversion macros.
For further reading I suggest Chris Maunder's article about "Unicode, MCBS and Generic text mappings" at http://www.codeproject.com/cpp/unicode.asp
monrobot13 wrote:
Also, this is off topic from the subject, but is there anything like CString for ATL?
If you want something that comes with the ATL library I can't think of anything besides the CComBSTR, but I guess that is not what you are looking for.
--
Roger
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If you're using ATL 7.1 (VC++.NET 2003), then ATL has a common CString it shares with MFC.
If you're using earlier versions (eg 3, from VC++6), then you can use WTL3.1 or 7.x which has a CString class also, somewhat lighter than using MFC in your app!
Steve S
Developer for hire
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I'm still using the VC6, but it's good to know the alternatives.
--
Roger
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Thanks for all the replies everyone. I forgot I posted this question here.
- Aaron
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Hi
I am using a COM component to upload files to website. I am writing all the files to a folder using "Binary Access Write" (VB) method.
I am facing a problem. When a large file is being uploaded, no other file can be uploaded. The page times out.
I want to make my site able to upload files simultaneously.
Please give me advice on how to solve the problem.
Thanks in advance.
Mandar Date,
Software Engineer
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Two questions:
One, can interface methods have default parameters? i.e.
HRESULT MyMethod ([in] int size = 0) Two, can a class that implements an interface have a constructor with paramaters?
Thanks!
- Aaron
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monrobot13 wrote:
Two questions:
One, can interface methods have default parameters? i.e.
HRESULT MyMethod ([in] int size = 0)
Yes. Have a look at the MIDL keywords 'optional' and defaultvalue' in MSDN.
Two, can a class that implements an interface have a constructor with paramaters?
Regarding the C++ synthax and if you mean whether it will compile or not, the answer is yes.
I don't see the use of it though. When the ClassFactory creates the object the default constructor will get called. It should be possible to modify the ClassFactory to call a constructor with parameters, but I don't know how much work that would be. I have a feeling that it would be much work for nothing since the same constructor will be called every time the object is created. Even if you take the long way of reading the registry by yourself to get the CLSID, calling CoGetClassObject and creating the object through the IClassFactory::CreateInstance method, there is no way you can pass parameters that can determine which constructor to call from the ClassFactory. Not through the COM-interfaces anyway. Technically you could have information elsewhere, e.g. in the registry, but I consider that an unstable solution and NOT recommendable.
Consider who is responsible for that kind of information; if it's you, you can reproduce that information in your default constructor and if your user is responsible you have no control of the information and that would require a lot of error checking and fault tolerant code. And if it doesn't work, you would still be the one the user blames. 
--
Roger
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Thanks for the informative reply.
- Aaron
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hi
One - Yes, An interface method can have parameters with default values provided the parameter shud be optional too. The parameter settings while creating the function defenition in IDL is as fllows:
[in] short i, [in] short j, [in, out, optional, defaultvalue(117)] short* k, [out, retval] short* l
and the c++ function signature will be:
STDMETHODIMP MyClass::Test(short i, short j, short *k, short *l)
Two - A class that implimets an interface can have constructor with parameters. But no way to use that. If you use CoCreateInstance to create the client then we can't use the c++ class name directly and so cunstructor parameter also. Only way where we can use the c++ class name to create the com class is CComObject<MyClass>. But even this CComObject does not accept constructor initializers.
rgds...mil10
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Thanks much, the information is much appreciated.
- Aaron
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Hi,
I'm really new to DCOM but my boss wants me to get into it. so here's my question:
I currently have a SDI MFC application which is a media player with DirectX, but that's beside the point. The thing is my boss wants me to implement the current application with some diagnostics software which has to call my application and pass along some values. The idea is to use DCOM as the interface between both applications but I'm kind of at a loss what I need to do now though. I've been reading some DCOM tutorials and I kind of understand how it works but I haven't been able to really find what I need to do to convert my current application to a component which understands messages it's sent. I'd be very greatful if anyone could help me or point me to some text on the internet which could help me.
-Paul
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hi,
this is my observation , correct me if i am wrong .
I was defining a UDT which consist of a
[uuid(D8B3861A-74C6-11d2-0000-00C04FB17CDB)]
struct _BSSID_INFO
{
BSTR name;
short grade;
//classification type;
VARIANT_BOOL graduate;
};
in the IDL file.
Now when i was compiling with Default Visual Studio IDE Compiler it gave the
following errors :-
error MIDL2072 : inapplicable attribute : [uuid] [ Struct '_BSSID_INFO' ]
error MIDL2072 : inapplicable attribute : [uuid] [ Struct '_BSSID_INFO' (
Parameter 'bssid_info' ) ]
warning MIDL2039 : interface does not conform to [oleautomation] attribute :
[ Parameter 'bssid_info' of Procedure 'get_BSSID_INFO' ( Interface
'ICWiFiMgr' ) ]
but when i compiled with new vesrion of compiler and replaced it with new
MIDL.exe in the bin dir of VS6 it compiled correctly.
Any Inputs
--
Tarun..
Knowledge Seeker............
**********************************************************************
Tarundeep Singh Kalra
(tarundeep1976_nospam_at_yahoo_dot_nospam_dot_com)
tarun_at_tarunsadhana_dot_com
visit:www.tarunsadhana.com
*************************************************************************
Blue Pill or Red Pill........??
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dear,
i use .net framework v1.0.3705. win 2000 sp 4. i try to registry my dll with regasm or regsvcs. but, i have an error.
"Strong name validation failed for assembly
'C:\WINNT\Microsoft.NET\Framework\v1.0.3705\RegAsm', The file may have been
tampared with or it was partially signed but not fully signed with the correct private key."
event if, i just run regasm or regsvcs from .net command prompt, i have a same error.
please help me sir/madam...i really appreciate for your help.
best regards
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hi,
I already saw this behavior when you referenced the System.EnterpriseServices without a strongname, the behavior of project act strangely, in design time the COM run smoothly but if you want to register your object into component services the problem occurs. The RegAsm utility show an error saying about strongname. The just add strongname to your project will solve your problem.
mark
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I am trying to implement a simple COM Application using Custome Interface and trying to get its object through CoCreateInstace(....). But it can get pointer to IUnknown interface but not the pointer to the COM Object. \
But the above scenerio works well in case of COM DLL Application.
Kindly help me in this regard.
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Have you built and registered your proxy/stub library?
If you're using an Automation-compliant interface (only using types defined for the VARIANT type) and the Automation marshaller, this step is not necessary as long as you have registered your type library.
When you make an out-of-process call, COM has to translate the call arguments from the source process to the destination process - this is called marshalling. This isn't necessary in-process as long as the components are loaded into the same apartment (if they load into different apartments or contexts, COM needs to marshal between them). The proxy/stub DLL contains two parts, a proxy and a stub. The proxy is loaded into the client's address space and impersonates the server for the client. The stub loads into the server's address space and impersonates the client for the server.
The Automation marshaller simplifies things a bit; it's able to generate a proxy and a stub from the type library.
Stability. What an interesting concept. -- Chris Maunder
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First off I'm new to COM programming so maybe this question is foolish.
In the class I'm writing I need some strings so I'm using the CComBSTR class (I'm using ATL) for my strings. If I need to convert that item to a regular char can I use the OLE2A (and it's realated macros) to do this? I'm doing OLE2CA(bsString.Copy()) to convert it. Will this work?
Also are BSTR's the best types to use for function paramters when implementing the functions of the interface?
Thanks!
- Aaron
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Yes, be sure and use the USES_CONVERSION macro before using any of the ATL conversion macros.
monrobot13 wrote:
Also are BSTR's the best types to use for function paramters when implementing the functions of the interface?
Yes
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