USES_CONVERSION - COM Discussion Boards

13-May-04 11:35

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

Andrew Quinn AUS17-May-04 5:22

Andrew Quinn AUS

17-May-04 5:22

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 Smile | :)

- Andy

Roger Stoltz17-May-04 11:35

Roger Stoltz

17-May-04 11:35

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

Steve S17-May-04 23:26

Steve S

17-May-04 23:26

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

Roger Stoltz18-May-04 0:20

Roger Stoltz

18-May-04 0:20

I'm still using the VC6, but it's good to know the alternatives.

--
Roger

Re: Thanks Everyone

monrobot1320-May-04 6:49

Writing files simultaneously

20-May-04 6:49

Thanks for all the replies everyone. I forgot I posted this question here.

- Aaron

13-May-04 0:14

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

Interface Methods

monrobot1312-May-04 18:47

12-May-04 18:47

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

Roger Stoltz12-May-04 22:14

Roger Stoltz

12-May-04 22:14

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. Eek! | :eek:

--
Roger

monrobot1313-May-04 11:01

13-May-04 11:01

Thanks for the informative reply.

- Aaron

Milton Karimbekallil12-May-04 23:13

Milton Karimbekallil

12-May-04 23:13

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

monrobot1313-May-04 11:02