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Hi,
I have a doubt regarding memory sharing in a COM object.
Background: Recently we shifted to VS2005. Hence the dll written in VC6 is no longer directly useful. I might have to write a COM wrapper to access this dll. The application would be working with huge files and I want only a single copy maintained across my application. The dll should actually read the file and after the error checking send the a pointer of the memory to my application.
My question:
1) Is it possible to do it with COM?
2) What would happen if my COM object memory is on a remote server?
3) Does the COM object copy the memory and send it to the requested application or does it just pass the reference.
My intention is to maintain a single place of memory where the file data would be read and used.
Please let me know how can I achieve this through COM. Any links would be useful.
Regards,
Arti Gujare
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ArtiGujare wrote: Recently we shifted to VS2005. Hence the dll written in VC6 is no longer directly useful.
I don't understand that? Your old C++ code should be able to still do the following in a VS2005 C++ project.
ArtiGujare wrote: The dll should actually read the file and after the error checking send the a pointer of the memory to my application.
led mike
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When I said we shifted to VS2005 I meant that the application using the dll was previosly written in VC6 and dll too was written in VC6. Now the application has to be written in VS2005 and still use the VC6 dll. My typical use case is:
1) Application send the file name to the dll.
2) dll reads the file at that mentioned filepath and does some file checks
3) if the file is in expected format, the dll returns the pointer pointing to the file data to the applictaion.
I hope it looks clear now.
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I see no information in there that would keep you from accomplishing that using VS2005 C++ projects.
led mike
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What about :
2) What would happen if my COM object memory is on a remote server?
3) Does the COM object copy the memory and send it to the requested application or does it just pass the reference.
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For (3): You cannot pass a reference to memory across machines, that makes no sense at all. Therefore the memory is copied.
I have no idea why you are fixated on COM. Nothing in your requirments demands using COM. Without a requirement I would not choose to include the complexity and overhead associated with COM. In other words I would only use COM as a last resort.
led mike
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Hi Led,
I tried adding the VC6dll in my VS2005App using "Add Reference". I could not add it. I got the message
"A reference to "<dllpath>" could not be added. Please make sure that the file is accesible, and that it is a valid assembly or COM component"
I googled around a bit with this message and I found that I cannot simply use the VC6dll in my VS2005App. Many links suggested that I might have to wrap the dll in a COM component in order to use it. Hence the COM usage. Otherwise if there is an alternative to bypass COM wrapping I would be more than happy to do the same.
Any suggestions?
Thanks and Regards,
Arti Gujare
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Is the DLL already implementing a COM object? If so then it should work no problem.
I thought one of the ideas behind com was portable objects.
If it's not a com DLL then there's no "Add Reference" that will load the DLL. You need to link
to it (implicitely or explicitely using LoadLibrary() or similar). If it uses MFC you may have
problems. If it uses the CRT you may have problems as well since you'll have mixed versions
between the app and the DLL.
Mark
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ArtiGujare wrote: I tried adding the VC6dll in my VS2005App using "Add Reference".
"Add Reference" is for adding .NET assemblies in a "Managed" Project. You are in the C++ forum indicating that your project is a "Native" project. Therefore you do not add a reference to the DLL. You link to it using a .Lib file just as before. Using a DLL from a C++ project is pretty basic stuff, why are you having problems with this? Perhaps if you give us more information about your level of experience we might provide more targeted information.
led mike
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Hi!
Does anyone know why would an extension DLL not load when using the following code?
if ( AfxLoadLibrary( "MyDLL.dll" ) == NULL )
AfxMessageBox( "Error loading library." );
So, MyDLL.dll is an extension DLL. AfxLoadLibrary always returns NULL, even though the calling process and MyDLL.dll are in the same directory.
Any help will be greatly appreciated!
Thanks in advance!
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What does your DllMain look like in the extension DLL? Is initialization failing there?
The app and the DLL are using the DLL version of MFC, correct?
Mark
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This is how my DllMain looks like:
extern "C" int APIENTRY
DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved)
{
UNREFERENCED_PARAMETER(lpReserved);
if (dwReason == DLL_PROCESS_ATTACH)
{
TRACE0("MYDLL.DLL Initializing!\n");
if (!AfxInitExtensionModule(MyDLL, hInstance))
return 0;
new CDynLinkLibrary(MyDLL);
}
else if (dwReason == DLL_PROCESS_DETACH)
{
TRACE0("MYDLL.DLL Terminating!\n");
AfxTermExtensionModule(MyDLL);
}
return 1;
}
I even put these lines of code right at the begining of DllMain:
CFile log;
log.Open( "log.001", CFile::modeCreate | CFile::modeWrite, NULL );
log.Write( "@", 1 );
log.Close( );
I ran the program using the new version of mydll.dll and NO log.001 was created.
So DllMain does not get executed.
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You shouldn't need to write a log file. "MYDLL.DLL Initializing!" should show up in your debug
output window. You could put a breakpoint in there as well.
It's a mystery  Have you tried David Crow's suggestion?
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Problem solved!!!!!!!!!!
MyDLL.dll was using another dll which did not exist.
Thank you for your time!
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Eikthrynir wrote: MyDLL.dll was using another dll which did not exist.
Cool 
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Eikthrynir wrote: ...even though the calling process and MyDLL.dll are in the same directory.
Just for grins, try specifying an absolute path to mydll.dll.
Is your app multithreaded?
"Approved Workmen Are Not Ashamed" - 2 Timothy 2:15
"Judge not by the eye but by the heart." - Native American Proverb
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I am building a client server application (socket based) in which i have to transfer data between different systems (different harware and operating systems). After some survery I have found that XDR is a library which provides data potability amoung various operating systems (windows/unix) but i cant found any resource/example to use XDR in VC6. Please provide a link/etc of XDR or any other free library that provides reliable cross plateform communication and dataportability using VC6, on the other side (unix) simple c++ will be used.
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Dear All,
My service program is not able to interact with desktops. Why ?
Can any one answer this ?
Thanks.
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Sakthiu wrote: My service program is not able to interact with desktops. Why ?
Have you configured it to do so?
"Approved Workmen Are Not Ashamed" - 2 Timothy 2:15
"Judge not by the eye but by the heart." - Native American Proverb
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I am using list control (report view)
in windows List control headers contain a triangle shape which moves its direction when we click on the respective header showing sort order how can this delta be inserted in header?
An other query please
Is it possible to have multiple lines in an item or subitem of list control?
I would be extremly thankful for providing the solutions to above problems.
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pc_dev wrote: in windows List control headers contain a triangle shape which moves its direction when we click on the respective header showing sort order how can this delta be inserted in header?
It's not built-in to the control but you can owner-draw the header and add one yourself.
Mark
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Not sure but I did this in the past and maybe did it with an image rather than owner draw.
led mike
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You can put images in column headers? I'm going to look into that. I need something similar
Thanks man,
Mark
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Yes found the old project. Used a ImageList and then:
HDITEM hItem;
ZeroMemory( &hItem, sizeof(hItem));
hItem.mask = HDI_IMAGE | HDI_FORMAT;
_pList->GetHeaderCtrl()->GetItem( nCol, &hItem);
hItem.iImage = nImg;
hItem.fmt = HDF_LEFT | HDF_IMAGE | HDF_STRING | HDF_BITMAP_ON_RIGHT;
led mike
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Cool! Thank you!
It's as easy as tab controls
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