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Thank you Mark for your response! So to simplify the meaning of the value class is that it is the same as structures in VB.Net that can’t be inherited, and the “ref class” can be inherited form the other “ref classes”. I think I got it now!
And again, thank you for clearing the confusion I had!
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VBDT wrote: the meaning of the value class is that it is the same as structures in VB.Net that can’t be inherited, and the “ref class” can be inherited form the other “ref classes”.
Yes!
Cheers,
Mark
Mark Salsbery
Microsoft MVP - Visual C++
![Java | [Coffee]](https://codeproject.freetls.fastly.net/script/Forums/Images/coffee.gif)
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One more question I would like to ask. As what I read about “ref class” and “value class” it appears that these are only used in C++/CLI projects and these keywords specify that the classes (data types) are managed and these keywords are not used in native C++ code. Is this the case?
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Mark you just made my day! Thank you for your help. Your explanation was awesome, and yes it makes a lot sense about ref and value classes to define them class and structure respectively comparing with VB.Net. Thank you for your help very much!!! 
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Hey again, gang,
Once again, I have a question that I'm sure comes from me just missing something simple. I googled around a bit for this, but wasn't able to find anything that addressed this directly, just related tasks that didn't quite give me what I needed. If I'm just being thick-headed, I'd be more than happy with just being slapped with a link so I can learn on my own.
I'm dealing with a large collection of .h and .cpp files that together make up a bunch of classes that assist with TCP communication for a large project. Several different programs in the project use these files, and they currently do so by just #include-ing them in their own code. Consequently, a change to one packet class makes it necessary to recompile every project that depends on it. I believe that it would be better to roll all of these files into a DLL that each of the other projects can link against.
I have written my own DLLs a few times, but have always done so by creating a namespace in the DLL project and adding classes to it directly, but I can't do that here since the classes are already defined in the existing headers. How can I include these existing classes in my DLL project and make them visible from its namespace? Just #include-ing them doesn't seem to be enough, since I get a bundle of linker errors when I try to use the resulting DLL in other projects.
Could someone please clue me in or point me to a resource on this? Thanks a million!
(I'm using Visual Studio 2008 with C++/CLI. The code I'm trying to roll up is written in C++, and is cross-platform enough to be compiled on Windows and Linux boxes. I'm trying to create a DLL out of them to be used in other C++/CLI projects, and let the Linux guys handle it their own way on their side, so I don't want to modify the existing code and make it Windows-only.)
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I did think my goal was to create a .NET assembly, but perhaps I was wrong about that as well. If that is the case, I'm very sorry that I put this up in the wrong place. I hate being the forum dolt. 
I need to study the links you provided a little more closely to be sure, but it does look like that is the information I need. If I can figure out how to use dllexport to expose a class outside of the DLL, I'll be set.
Thank you very much for the lead, Mike. (Har!)
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I am Using Visual c++ 2005
I need to make ab choice of all my Printing options
I have a Problem how to fill into my comBobox All Orientation Parper
I try This
this->paperorientation->DataSource = System::Enum::GetValues(GetType(PaperOrientation))
I have a message CrystalDecisions::Shared::PaperOrientation: Illegal use of this type as an expression.
I do not what to do
Can you help me
I need to fill my Paper Orientation, PAper Size, Paper Duplex ComboBoxes
Help needed
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Hello,
I want to use RAR compression in my MC++ project ...
Please help me.
Every new thing you learn,Gives you a new personality.
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Have you tried googling around?
"The clue train passed his station without stopping." - John Simmons / outlaw programmer
"Real programmers just throw a bunch of 1s and 0s at the computer to see what sticks" - Pete O'Hanlon
"Not only do you continue to babble nonsense, you can't even correctly remember the nonsense you babbled just minutes ago." - Rob Graham
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I have a medium sized (27 projects) solution which has a mixture of project types, libs (both MC++ and C++), DLL's (both MC++ & C++) and exes all MC++.
I am considering upgrading the project to vc 2008 mainly because this is the only project that I look after that needs VC 2003 and would like to use one development environment for everything. (have successfully upgraded all my VC2005 projects to VC2008)
During the upgrade I was considering doing a 'proper' upgrade of all the code e.g. changing __gc class to ref class and using gcnew as required.
Anyone know of any undocumented issues that might make this upgrade a failure or accelerate hair loss!
Robin
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I personally would take the time to upgrade all the Managed Extensions
code to C++/CLI format. The old syntax is still supported (with a
compiler option) but the Managed Extensions are deprecated (and not
as clean to read/use as the C++/CLI format).
Mark
Mark Salsbery
Microsoft MVP - Visual C++
![Java | [Coffee]](https://codeproject.global.ssl.fastly.net/script/Forums/Images/coffee.gif)
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I am trying to use a cliext::list<> and am hitting various problems - apologies, its a long one - but stick with me . Before I start, I am using Visual Studio 2008 with service pack 1. I am (relatively) new to mixed mode programming - my background is pure C++ / MFC, etc - so it is entirely possible I am misunderstanding something. I have reduced my first problem to the following:
Header file:
#pragma once
#include <cliext/list>
private ref class TestClass
{
cliext::list<int> ^ m_list;
public:
TestClass(void);
};
.cpp file:
#include "StdAfx.h"
#include "TestClass.h"
TestClass::TestClass(void)
: m_list(gcnew cliext::list<int>())
{
}
Produces this little lot... (project name is LNK2022)
1>------ Build started: Project: LNK2022, Configuration: Debug Win32 ------
1>Linking...
1>TestClass.obj : error LNK2022: metadata operation failed (80131188) : Inconsistent field declarations in duplicated types (types: cliext.impl.list_impl<int,0>; fields: _Myhead): (0x0400000a).
1>TestClass.obj : error LNK2022: metadata operation failed (80131188) : Inconsistent field declarations in duplicated types (types: cliext.impl.list_impl<int,0>; fields: _Mysize): (0x0400000b).
1>TestClass.obj : error LNK2022: metadata operation failed (80131188) : Inconsistent field declarations in duplicated types (types: cliext.impl.list_impl<int,0>; fields: _Mygen): (0x0400000c).
1>TestClass.obj : error LNK2022: metadata operation failed (801311D7) : Differing number of fields in duplicated types (cliext.impl.list_impl<int,0>): (0x02000023).
1>TestClass.obj : error LNK2022: metadata operation failed (8013118B) : Inconsistent implemented interfaces in duplicated types (types: cliext.impl.list_impl<int,0>; interfaces: System.Runtime.CompilerServices.CallConvStdcall): (0x09000001).
1>TestClass.obj : error LNK2022: metadata operation failed (8013118B) : Inconsistent implemented interfaces in duplicated types (types: cliext.impl.list_impl<int,0>; interfaces: System.IDisposable): (0x09000002).
1>TestClass.obj : error LNK2022: metadata operation failed (8013118B) : Inconsistent implemented interfaces in duplicated types (types: cliext.impl.list_base<int,0>; interfaces: System.Runtime.CompilerServices.CallConvFastcall): (0x09000003).
1>TestClass.obj : error LNK2022: metadata operation failed (8013118B) : Inconsistent implemented interfaces in duplicated types (types: cliext.impl.list_base<int,0>; interfaces: System.Runtime.CompilerServices.CallConvThiscall): (0x09000004).
1>TestClass.obj : error LNK2022: metadata operation failed (8013118D) : Inconsistent layout information in duplicated types (cliext._Dehandle<int>): (0x02000021).
1>TestClass.obj : error LNK2022: metadata operation failed (8013118D) : Inconsistent layout information in duplicated types (cliext.is_handle<int>): (0x02000022).
1>LINK : fatal error LNK1255: link failed because of metadata errors
1>Build log was saved at "file://i:\dev\ians stuff\LNK2022\LNK2022\Debug\BuildLog.htm"
1>LNK2022 - 11 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Does anyone have any ideas? If I initialise the list in the header, the program compiles and links ok.
Ok, fine, I can live with that unless I want to hide my implementation of the constructor in the .cpp to reduce dependencies (my code is more complicated).
Anyway, next problem...
Header file:
#pragma once
#include <cliext/list>
private ref class TestClass
{
ref struct SInside
{
int mem1;
};
cliext::list<SInside ^> ^ m_list;
public:
TestClass()
: m_list(gcnew cliext::list<SInside ^>())
{}
};
No particular rocket science here, a nested struct being used as the type for the list container. Note initialisation in header - constructor removed from .cpp 'cos of point one above.
As soon as we construct the an object of type TestClass with the following in the form constructor:
TestClass ^ tmp = gcnew TestClass();
I get a message box with the following (my test app compiles to LNK2022.exe):
An unhandled exception of type 'System.TypeLoadException' occurred in LNK2022.exe
Additional information: Access is denied: 'Microsoft.VisualC.StlClr.IList`1[TestClass+SInside]'.
I am really not sure even what this is trying to tell me, but what I do know - after a lot of searching and head scratching (and randomly moving code) - if I move the nested struct outside of the class declaration, everything is fine. Again, in my real example this reduces my encapsulation, and I would rather not do it if possible.
If I move the nested struct to a public section of the class, all is ok too. I have tried the equivalent using std::list, and again all is fine (with a list of objects or pointers).
Question is, am I trying to do something that is not supported, have I done something obviously wrong, or is this a bug in the STL.net library?
<div class="ForumMod">modified on Wednesday, August 27, 2008 9:38 AM</div>
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I think you need to make ref struct SInside access level "public" due to the usage of generics in STL/CLR. However, if this ref struct SInside is only going to be accessed within the same assembly, you can make it's access level "internal" or "protected public".
"We make a living by what we get, we make a life by what we give." --Winston Churchill
modified on Thursday, August 28, 2008 3:39 PM
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I am connecting Sqlserver2000 with VC++6.0(MFC) and ERROR when update information. please help me. thanks very much
----------------------------------------------------
void CReadDBDlg::OnRead()
{
// TODO: Add your control notification handler code here
CDatabase database;
CString SqlString;
CString sCatID, sCategory;
CString sDriver = "SQL Server";
CString sDsn;
CString sFile = "nhanvien_DATA.mdf";
int iRec = 0;
sDsn.Format("Driver={SQL Server};Server={EZITWK115};" "Trusted_Connection=no;""Database=NHANVIEN;Uid=sa;Pwd=sa;");
TRY
{
// Open the database
database.Open(NULL,FALSE,FALSE,sDsn,TRUE);
// Allocate the recordset
CRecordset recset( &database );
CString SS2 = "UPDATE nhan_vien SET hoten = 'nU' WHERE manv = '002' ";
//Execute query ====>> This is ERROR !!!
recset.Open(CRecordset::forwardOnly,
"{CALL " + SS2 + "}", CRecordset::executeDirect);
// Close the database
database.Close();
}
CATCH(CDBException, e)
{
// If a database exception occured, show error msg
AfxMessageBox("Database error: "+e->m_strError);
}
END_CATCH;
}
-------------
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PLEASE stop repeatedly posting this question.
There's no managed C++ in VC6 so you're posting in the WRONG PLACE!
Mark
Mark Salsbery
Microsoft MVP - Visual C++
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Hi,
I have created and maintain a VC++ .NET 2005 project that creates a dll for SQL server 2000/2005 extended stored proc.
For now it recomplies the source files(originally written in VC++ 6.0) but it required by me to use the existing COM dll written in VS6 from VC++ .NET 2005.
Is it even possible to call Com dll from VC++ .NET 2005?
If yes how can I do that?
I used to program in .NET but haven't done any intensive programming in years, so please if I ask stupid questions.
Please feel free to ask any other info.
Thanks in advance for your help.
-Amit
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amalhotr wrote: Is it even possible to call Com dll from VC++ .NET 2005?
Yes.
amalhotr wrote: I used to program in .NET but haven't done any intensive programming in years
Ok, but are you an experienced C++ developer? If not then you are not prepared to do COM development in C++. First one learns C++, then one learns other things like how to do Win32 COM development.
amalhotr wrote: so please if I ask stupid questions.
There is no such thing as a stupid question. However there are questions posted into the wrong forum. This forum is about doing managed development for the .NET platform using C++/CLI. That does not appear to be what your question is about.
For native C++ questions there is the Visual C++ / MFC forum
For COM questions there is the COM forum
Either one of those would probably have been a more appropriate forum for your question.
led mike
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Thanks for your help.
I'll post it in COM forum.
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Please Guide I command "Update" Sql2000 in VC++6.0.
thanks very much
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I have the same question as the guy below this form, but my question has to do with MDIparents and childs. I followed a guide that told you how to, but I kept getting errors everytime I built it.
http://www.functionx.com/vcnet/Lesson07.htm[^]
I used this guide, but it gave me errors saying its a mix between Managed and nonManaged C++.
I'm new to MDIParents+childs and was wondering if i can get some help with this.
And when i used what you told the guy below me i got these 2 errors.
System.InvalidOperationException: Starting a second message loop on a single thread is not a valid operation. Use Form.ShowDialog instead.
System.InvalidOperationException: Form that is already visible cannot be displayed as a modal dialog box. Set the form's visible property to false before calling Show.
I did what it said both times, but still got same problem.
modified on Sunday, August 24, 2008 11:02 PM
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I don't know what you already tried to do.
But I think it is quite easy to add a MDI child form.
In the MDI-Parent, set IsMdiContainer = true.
And to create a new Child (e.g. from a event handler
within the MDI-Parent):
Child^ child = gcnew Child();
child->MdiParent = this;
child->Visible = true; Alex
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Hi, I need use two forms in application. Is some easy way exists? I do that in Delphi, but in C++/CLI Win Form app is something understandable. I was googling for some easy practise, but not found it.
Is there something who help me with piece of code for two forms?
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you can use multiple forms in C++/CLI. Just right click on your project and click "Add new Item..."
Don't be overcome by evil, but overcome evil with good
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