Error trying to call a C# DLL from a C++ console app

Question

Error trying to call a C# DLL from a C++ console app

DonBaechtel-7903 191

I am on Windows 10 with VS 2022.

I want to call a C# DLL from a C++ app.

I am trying to register the C# DLL using regasm.

I am getting the following error:

C:\Users\dbaec\OneDrive\Forex\C++_App\C#_DLL\obj\x64\Debug\net6.0-windows7.0>regasm.exe /register "C:\Users\dbaec\OneDrive\Forex\C++_App\C#_DLL\obj\x64\Debug\net6.0-windows7.0\c#_DLL.dll"

Microsoft .NET Framework Assembly Registration Utility version 4.8.9037.0

for Microsoft .NET Framework version 4.8.9037.0

RegAsm : error RA0000 : Could not load file or assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.

How do I fix this?

How do I call a C# DLL from a C++ app?

Thanks.

RLWA32 49,636 Reputation points

2025-06-16T17:22:13.8533333+00:00

If your intent is to create a COM server using .Net (not .Net Framework) that can be instantiated by a COM client written in native C++ (not C++/CLI) I suggest you start by reading https://learn.microsoft.com/en-us/dotnet/core/native-interop/expose-components-to-com. The procedure to create and register a .Net 5+ COM Server has changed and regasm.exe is only used for .Net Framework.

Of course, if you use C++/CLI for the application that consumes the .Net assembly then COM would not be needed.

By the way, with VS2022 you should probably be working with .Net 8 or .Net 9. .Net 6 has been out of support for quite some time.
DonBaechtel-7903 191 Reputation points

2025-06-17T21:57:40.7+00:00

RLWA32:

I cannot follow all of the instructions in the post..
https://learn.microsoft.com/en-us/dotnet/core/native-interop/expose-components-to-com.The steps are incomplete. See steps 7, 8, and 9.Is there a more complete example?

Can you explain the steps?

I'm afraid it won't work.
RLWA32 49,636 Reputation points

2025-06-17T22:27:19.1433333+00:00

@DonBaechtel-7903, There are numerous complete code samples that might be helpful to you at https://github.com/AaronRobinsonMSFT/COMInterop.A couple of key differences between COM support in the .Net Framework and .Net 5+ --

As I mentioned earlier, regasm.exe is not used for COM registration. A properly constructed .Net project that builds a COM server will also create an assembly named something like Yourproject.comhost.dll. This should be registered using regsvr32.exe.

The .Net Framework supported type libraries. This support is not present in .Net projects. That is why the samples use an IDL file to create a type library which can be embedded in the COM server as a resource.

You may also find the extensive discussion contained in the thread at https://learn.microsoft.com/en-us/answers/questions/2259135/how-to-register-net-8-build-activex-so-that-test-p to be helpful.
DonBaechtel-7903 191 Reputation points

2025-06-17T23:20:17.9433333+00:00

The **COMInterop **project that you mentioned has a Cs demo calling a Cs DLL.

It is very important that I have a Cpp program calling a Cs DLL, and I am not sure how to construct it.

I need to add a Cs DLL to the MetaTrade5 platform, which is all Cpp.

Can you help? Too many details are unclear.

Accepted answer

4 additional answers

Your answer

RLWA32 49,636 Reputation points

2025-06-16T17:22:13.8533333+00:00

If your intent is to create a COM server using .Net (not .Net Framework) that can be instantiated by a COM client written in native C++ (not C++/CLI) I suggest you start by reading https://learn.microsoft.com/en-us/dotnet/core/native-interop/expose-components-to-com. The procedure to create and register a .Net 5+ COM Server has changed and regasm.exe is only used for .Net Framework.

Of course, if you use C++/CLI for the application that consumes the .Net assembly then COM would not be needed.

By the way, with VS2022 you should probably be working with .Net 8 or .Net 9. .Net 6 has been out of support for quite some time.
DonBaechtel-7903 191 Reputation points

2025-06-17T21:57:40.7+00:00

RLWA32:

I cannot follow all of the instructions in the post..
https://learn.microsoft.com/en-us/dotnet/core/native-interop/expose-components-to-com.The steps are incomplete. See steps 7, 8, and 9.Is there a more complete example?

Can you explain the steps?

I'm afraid it won't work.
RLWA32 49,636 Reputation points

2025-06-17T22:27:19.1433333+00:00

@DonBaechtel-7903, There are numerous complete code samples that might be helpful to you at https://github.com/AaronRobinsonMSFT/COMInterop.A couple of key differences between COM support in the .Net Framework and .Net 5+ --

As I mentioned earlier, regasm.exe is not used for COM registration. A properly constructed .Net project that builds a COM server will also create an assembly named something like Yourproject.comhost.dll. This should be registered using regsvr32.exe.

The .Net Framework supported type libraries. This support is not present in .Net projects. That is why the samples use an IDL file to create a type library which can be embedded in the COM server as a resource.

You may also find the extensive discussion contained in the thread at https://learn.microsoft.com/en-us/answers/questions/2259135/how-to-register-net-8-build-activex-so-that-test-p to be helpful.
DonBaechtel-7903 191 Reputation points

2025-06-17T23:20:17.9433333+00:00

The **COMInterop **project that you mentioned has a Cs demo calling a Cs DLL.

It is very important that I have a Cpp program calling a Cs DLL, and I am not sure how to construct it.

I need to add a Cs DLL to the MetaTrade5 platform, which is all Cpp.

Can you help? Too many details are unclear.

Answer 1

RLWA32 49,636

I created a small demo solution in VS2022 that contains 3 projects. The NetServerTypes project uses an IDL file to create a type library. The NetServerTest project builds the C# COM Server, embeds created type library as a resource and also uses a post-build event to register the server and the type library. COM registration requires elevated privileges so run Visual Studio as Administrator when you build the solution. The CppClient project is a minimal C++ console application that imports the registered type library to generate required headers. It instantiates the COM object and calls methods and gets a property.

The demo is at https://1drv.ms/u/c/c389bf4121acea69/EfUvHqqc66tNjGT-AJOGPBEBfDHhtc3IfbfbnjZTRF9elw?e=oRkujI

DonBaechtel-7903 191 Reputation points

2025-06-21T19:41:37.3166667+00:00

I got 3 fatal errors trying to rebuild NetServerDemo.sln.

Can you tell me how to fix these errors so that I can run the demo?

Severity Code Description Project File Line Suppression State Details

Error (active) MSB3075 The command "regsvr32 /s C:\Users\dbaec\Downloads\NetServerDemo\NetServerDemo\NetServerTest\bin\Debug\net8.0\NetServerTest.comhost.dll" exited with code 5. Please verify that you have sufficient rights to run this command. NetServerTest C:\Users\dbaec\Downloads\NetServerDemo\NetServerDemo\NetServerTest\NetServerTest.csproj 19

Severity Code Description Project File Line Suppression State Details

Error C3506 there is no typelib registered for LIBID '{1C538303-191B-4994-8F70-9A55B9AB2D99}' CppClient C:\Users\dbaec\Downloads\NetServerDemo\NetServerDemo\CppClient\CppClient.cpp 11

Severity Code Description Project File Line Suppression State Details

Error C1104 fatal error importing libid: '1C538303-191B-4994-8F70-9A55B9AB2D99' CppClient C:\Users\dbaec\Downloads\NetServerDemo\NetServerDemo\CppClient\CppClient.cpp 11
RLWA32 49,636 Reputation points

2025-06-21T20:32:40.3666667+00:00

Make sure that before you extract the content of the downloaded zip file that you unblock it.

After unblocking and extracting the content also make sure that you run Visual Studio with elevated privileges as Administrator. This is needed for COM registration.

The solution and the 3 projects are configured with dependencies so that they build in the correct order. The build order should be as shown here -

NetServerTypes should build first, followed by NetServerTest and finally CppClient. The easiest way to ensure this happens is to use Build->Build Solution from the VS2022 main menu.

This is what the build output should look like -

Executing the CppClient console application should produce these results -
DonBaechtel-7903 191 Reputation points

2025-06-21T21:59:23.8333333+00:00

After running VS in Administrator mode, the Demo solution built OK, and I am having some success. Thanks.

I will conduct a test with the MetaTrader5 platform (C++) to ensure everything is compatible with it soon.

I will be running a sophisticated C++/C# interface exchanging many different data types across the interface. I will be running X64 mode. Do you know of any good guidance about the compatibility of various data types between C++ and C#? For example, I know that a long in X64 is a long long in C++. Will this affect the IDL description?
RLWA32 49,636 Reputation points

2025-06-21T22:58:38.34+00:00

Generally speaking interop marshaling for COM is largely similar to what is documented for P/Invoke. However, the COM marshaler does differ in some ways. For example, notice in the demo how C# strings are marshaled back to C++ as BSTR types. Arrays are also another area where marshaling can differ. Also, for a managed COM server the choice of interface types is often dual or dispatch. Consequently, the data types must be compatible with those supported by the system default type library marshaler. And yes, the IDL must be written to reflect the appropriate equivalent types with respect to the the managed server. The BSTR parameters in the demo are indicative of that.

Microsoft's overview of interop marshaling are at https://learn.microsoft.com/en-us/dotnet/framework/interop/interop-marshalling

DonBaechtel-7903 191

Now I have a vexing problem.

I added two new methods to the C#, IDL, and C++ files.

The IDL looks like:

interface ITestObj : IDispatch

{

[id(1), propget] HRESULT Name([out, retval] BSTR* pbstrName);

[id(2)] HRESULT Whoami([out] BSTR* pbstrwhoami);

[id(3)] HRESULT GetServerLocation([out] BSTR* pbstrLocation);

[id(4)] HRESULT **InitPG_DLL**([out] boolean* OK);

[id(5)] HRESULT ShareBar([in] double open, [in] double high,

	[in] double low, [in] double close, [out] boolean* OK);

}

Cs:

public interface ITestObj

{

    [DispId(1)]

    string Name { get; }

    [DispId(2)]

    void Whoami(out string strwhoami);

    [DispId(3)]

    void GetServerLocation(out string strpath);

    [DispId(4)]

    void **InitPG_DLL**(out sbyte OK);

    [DispId(5)]

    void ShareBar(double open, double high, double low, double close,

        out sbyte OK);

}

    public void **InitPG_DLL**(out sbyte OK)

    {   

        OK = 1; // Indicating success

    }

Even after Build Clean and Rebuild Solution:

The ShareBar method shows up in the *.tli and *.tlb files and works OK.

But the InitPG_DLL method does not show up in the *.tli or *.tlb file, and gets error:

Error C2039 'InitPG_DLL': is not a member of 'ITestObj' CppClient C:\Users\dbaec\Downloads\NetServerDemo\NetServerDemo\CppClient\PolishedGoldEA.cpp 43

Why? How can InitPG_DLL not be a member of ITestObj ?

DonBaechtel-7903 191 Reputation points

2025-06-21T23:20:09.82+00:00

Sorry, two "" around InitPG_DLL meant bolded. The "" are not in the code.
DonBaechtel-7903 191 Reputation points

2025-06-22T01:42:07.29+00:00

Breakpoints are not active in the C# (DLL) code? It says no symbols have been added.

The C# DLL does not appear in the Debug>Windows>Modules list.

How do I activate the breakpoints in the C# DLL source code?
DonBaechtel-7903 191 Reputation points

2025-06-22T02:27:36.7633333+00:00

It is strange,

If I register my ShareBar method as either [DispId(4)] or [DispId(5)] it work fine.

If I take the ShaBar method and copy it and change its name to something like ShareBa, and register it as [DispId(4)] or [DispId(5)], the ShareBar method will still work, but it says ShareBa is not a member of ITestObj, when clearly it is properly defined.

It appears that it doesn't matter what DispId is used, as soon as more than 4 methods are registered then the 5th does not appear in either the *.tli file or the *.tlb file.

I don't know why.

Each time a Build Clean and Rebuild Solution is tried and no luck.

What do you think the problem is?
DonBaechtel-7903 191 Reputation points

2025-06-22T02:48:12.6633333+00:00

It is strange,

If I register my ShareBar method as either [DispId(4)] or [DispId(5)], it work fine.

If I take the ShaBar method and copy it, and change its name to something like ShareBa, and register it as [DispId(4)] or [DispId(5)], the ShareBar method will still work, but it says ShareBa is not a member of ITestObj, when clearly it is properly defined.

It appears that it doesn't matter what DispId is used, as soon as more than 4 methods are registered, then the 5th does not appear in either the *.tli file or the *.tlb file.

I don't know why.

Each time a Build Clean and Rebuild Solution is tried, and no luck.

What do you think the problem is?
DonBaechtel-7903 191 Reputation points

2025-06-22T02:54:39.09+00:00

It appears that the problem that I am having with the *.tli and *.tlb files is that I renamed the Solution, *.cs file, and *.idl files.

Even with a Build Clean, it appears that the *.tli file is still working on old information and generating an obsolete *.tli and *.tlb files.

I did not change the UUID GUID or much of the original content. But once I renamed the files, the *.tli stopped updating.

Do you know why this is happening? Why doesn't the *.tli file generate from the renamed files?

I use your UUID GUIDS, but I don't want to stick with your *.dll and source file names.

Thanks.
RLWA32 49,636 Reputation points

2025-06-22T06:04:10.46+00:00
Share your misbehaving solution/projects that include all your changes with me so that I can build it on my system and see the details.

You can used the mixed mode debugger so that it will recognize breakpoints in both the C++ and C# code.

If you want to return a boolean (true/false) from the C# COM server to C++ the C# code could look like this -

[DispId(4)] Boolean InitPG_DLL(); [DispId(5)] void ShareBar(double open, double high, double low, double close, out Boolean OK);

and the corresponding IDL could be -

[id(4)] HRESULT InitPG_DLL([out, retval] VARIANT_BOOL* OK); [id(5)] HRESULT ShareBar([in] double open, [in] double high, [in] double low, [in] double close, [out] VARIANT_BOOL* OK);

The reason for the change is -
RLWA32 49,636 Reputation points

2025-06-23T08:36:44.65+00:00

The demo C# COM server exposes a COM object that implements a dual interface. The object supports early binding through its vtable (essentially defines the order in which methods appear in the interface) and late binding through the IDispatch interface which uses DISPIDs. This is reflected in the IDL of the NetServerTypes project and the type library that it creates. When the demo's C++ client application imports the type library the generated .tlh and .tli files use early binding. Consequently, the DISPIDs are not used in the generated header files since it is not going through IDispatch. The COM object's methods and properties are accessed through its vtable. That is probably the reason why you observed that changing DISPIDs had no effect.

Had different attributes been specified on the C++ client's #import directive to cause the generated .tlh and .tli headers to reflect late binding (i.e., use IDispatch) then correct DISPIDs would be critical and runtime errors would likely result from arbitrary changes to them.
DonBaechtel-7903 191 Reputation points

2025-06-23T12:50:04.8366667+00:00

RLWA32,

I rely on your expertise in this area to advise on the best techniques to use. Whichever works best with MetaTrader5 and has the lesser dependencies is what I would prefer. I will be running on Windows in x64 mode for MetaTrader5.

One area you could help with is identifying which components from the demo build that you provided need to be deployed with the DLL file to make it work in the target directory? Which DLLs, TLBs, TLIs, PDBs, etc., are needed to communicate with the DLL when it runs?

Thanks very much for your assistance.
RLWA32 49,636 Reputation points

2025-06-23T13:07:56.5833333+00:00

I mentioned earlier that I'm not familiar with MetaTrader5. So I'm not in a position to give you any guidance that is specific to this product or how it relates to the substance of your posted question.

Deployment should be the subject of a new Question. It is a different topic and a new Question will have greater visibility to the community.

At this point have your previously mentioned issues been resolved with respect to the C++ COM client and the .Net 8 C# COM server?
DonBaechtel-7903 191 Reputation points

2025-06-23T14:25:30.6766667+00:00

I am trying to build another Solution like your Demo.

I found where to change the Project build order, and the order is wrong.

I cannot find how to change the build order of the projects. How to do it is not obvious.

Can you tell me how to change the Project build order? What action do I take to do this?
DonBaechtel-7903 191 Reputation points

2025-06-23T14:33:20.6866667+00:00

In attempting to build a solution like your demo, I am getting an error,

I may have to send you a copy of my Solution. How do I send you a zip file?,

Error:

Severity Code Description Project File Line Suppression State Details

Error (active) MSB3073 The command "regsvr32 /s C:\Users\dbaec\OneDrive\Forex\pGoldDLL\bin\Debug\net8.0\NetServerTest.comhost.dll" exited with code 3. pGoldDLL C:\Users\dbaec\OneDrive\Forex\pGoldDLL\pGoldDLL.csproj 19
DonBaechtel-7903 191 Reputation points

2025-06-23T14:56:59.75+00:00

I cannot attach a Zip file of my dilution here.

How do I send my ZIP file to you?
RLWA32 49,636 Reputation points

2025-06-23T15:13:24.6933333+00:00

The demo controls the build order of the projects by explicitly setting project dependencies. The CppClient project depends on the NetServerTest project because it registers the needed type library. The NetServerTest project depends on the NetServerTypes project for the type library that will be embedded and registered.

With the solution opened and all projects loaded from the Visual Studio main menu select Project->Project Dependencies... which opens a tabbed dialog that you can use to both set dependencies and see build order.

For example,

All of the above resulting in -

You can share a zip file with Microsoft's OneDrive (or equivalent service) by uploading it and then posting a link to the shared file back in this thread. Or create a public repository on Github and post a link to that.
DonBaechtel-7903 191 Reputation points

2025-06-23T22:59:57+00:00

Thanks
DonBaechtel-7903 191 Reputation points

2025-06-23T23:26:04.7+00:00

I enabled Native code debugging in the DLL (C#) project, and I changed the Debugger Type in the Client (C++) project to Mixed (.Net Core), but the breakpoints in the C# source code are still disabled.

How do I get the C# breakpoints enabled?
DonBaechtel-7903 191 Reputation points

2025-06-23T23:31:51.9266667+00:00

I am trying to make your Demo project into my own by changing some names and GUIDs.

I changed the GUID in the libid in both the C++ code and the IDL file and now after Build Clean and Rebuild, I get an error.

How do I make the changes and get the Solution to rebuild?

Severity Code Description Project File Line Suppression State Details

Error (active) E1696 cannot open source file "C:/Users/dbaec/OneDrive/Forex/NetServerDemo/NetServerDemo/CppClient/x64/Debug/libid:052B67EF-917E-439A-A5A2-023A18FF7858.tlh" pGoldEA C:\Users\dbaec\OneDrive\Forex\NetServerDemo\NetServerDemo\CppClient\PolishedGoldEA.cpp 12

If I could make your Demo Solution my own with some changes, I would be Happy.

Not easy.
DonBaechtel-7903 191 Reputation points

2025-06-23T23:33:22.4233333+00:00

I am trying to make your Demo project into my own by changing some names and GUIDs.

I changed the GUID in the libid in both the C++ code and the IDL file, and now, after Build Clean and Rebuild, I get an error.

How do I make the changes and get the Solution to rebuild?

Severity Code Description Project File Line Suppression State Details

Error (active) E1696 cannot open source file "C:/Users/dbaec/OneDrive/Forex/NetServerDemo/NetServerDemo/CppClient/x64/Debug/libid:052B67EF-917E-439A-A5A2-023A18FF7858.tlh" pGoldEA C:\Users\dbaec\OneDrive\Forex\NetServerDemo\NetServerDemo\CppClient\PolishedGoldEA.cpp 12

If I could make your Demo Solution my own with some changes, I would be Happy.

Not easy.
DonBaechtel-7903 191 Reputation points

2025-06-23T23:44:28.2733333+00:00

Build errors:

3>C:\Users\dbaec\OneDrive\Forex\NetServerDemo\NetServerDemo\CppClient\PolishedGoldEA.cpp(12,9): error C3506: there is no typelib registered for LIBID '{052B67EF-917E-439A-A5A2-023A18FF7858}'

3>C:\Users\dbaec\OneDrive\Forex\NetServerDemo\NetServerDemo\CppClient\PolishedGoldEA.cpp(12,9): error C1104: fatal error importing libid: '052B67EF-917E-439A-A5A2-023A18FF7858'

Why will it not build a *.tlb file from my IDL file?
RLWA32 49,636 Reputation points

2025-06-24T01:20:24.0966667+00:00

Why will it not build a *.tlb file from my IDL file?

If the NetServerTypes project build is failing to create a type library there should be error messages in the Output pane.

Post the error messages and the content of the IDL file that you are using.
DonBaechtel-7903 191 Reputation points

2025-06-24T02:07:37.16+00:00
I cannot create a copy of your Demp Solution with the following changes:

different root directory

new Solution name

New project names

new source filenames

new GUIDs

I have tried several times and have failed each time.

Your Demo Solution design seems to be too fragile.
It may be do to the registering and not registering of some components,

I need to make the changes to fit the application.
I can't use your component names and want to change the GUID for uniqueness.

Can you suggest how I go forward from here?
DonBaechtel-7903 191 Reputation points

2025-06-24T02:09:59.4566667+00:00

55 errors at the moment.

Things have fallen apart.
DonBaechtel-7903 191 Reputation points

2025-06-24T02:16:30.4333333+00:00

I may have to start with your Demo Solution again and start making my changes again, and let you know when I get the first error messages.

This is hard.
RLWA32 49,636 Reputation points

2025-06-24T02:23:27.9233333+00:00

I asked you to post error messages and the IDL file you are using. Why didn't you provide the requested information?

Your Demo Solution design seems to be too fragile.

It was a demo designed to illustrate how to use a native C++ COM client to call a managed C# COM server. It works flawlessly. Whatever problems you are experiencing have resulted from changes you have made.

Can you suggest how I go forward from here?

I previously offered to look at your solution/projects if you shared them including all your changes. The offer still stands.
DonBaechtel-7903 191 Reputation points

2025-06-24T15:15:20.97+00:00

OK, I started your Solution over again.

I started with your NetServerDemo and ensured that it built and ran correctly.

I moved the Solution to a new directory and changed the name of the root directory and the name of the Solution.

I changed the name of the NetServerTest project to pGoldDLL, and the name of the *.cs file as well.

All built and ran OK.

Then on line 29 of the pGoldDLL.cs file, I changed the _name from "Test Object" to "Polished Gold DLL".

Now, when I build and run the application, the Console still says that the Name is "Test Object' !!

This is what I mean about fragile. Why is the Solution not building from the source code that I changed and rebult??

I also changed the Debugging modes in both the C# and C++ projects to Native code debugging and Mixed (.NET Core). Still, the breakpoint is deactivated in the C# source code. How do I get the breakpoints to work properly?

How do I send you a Zip archive of my Solution? I am unable to attach a ZIP file here.

I appreciate your assistance with this.
RLWA32 49,636 Reputation points

2025-06-24T15:21:04.1933333+00:00

How do I send you a Zip archive of my Solution? I am unable to attach a ZIP file here.

As I previously said, "You can share a zip file with Microsoft's OneDrive (or equivalent service) by uploading it and then posting a link to the shared file back in this thread. Or create a public repository on Github and post a link to that."
DonBaechtel-7903 191 Reputation points

2025-06-24T16:22:40.4733333+00:00

Shared access to the Zip archive on OneDrive of the solution

Share (file://DESKTOP-U2L6I8Q/Users/dbaec/OneDrive/Share)

https://1drv.ms/u/c/a6cd3deab1f26c7e/ETX_rLj32DZOnE8c4BPbXA8B5IQNjpk741ypKeG5yjwI-A?e=hdCXg7

THANKS.
RLWA32 49,636 Reputation points

2025-06-24T17:27:09.06+00:00

You failed to make all the necessary changes to reflect the various items that you renamed. That is why registration of the COM server failed and consequently the C++ client could not built.
RLWA32 49,636 Reputation points

2025-06-24T17:34:23.8833333+00:00

Updated project at https://1drv.ms/u/c/c389bf4121acea69/EaV-4dxmGhhJrcFAnQJ1cnUB19zVLWrhWjdVWRQOee8n-g?e=U3gWn3
DonBaechtel-7903 191 Reputation points

2025-06-25T00:50:38.38+00:00

One question:

When are the functions RegisterFunction and UnRegisterFunction used?

What is their purpose?
DonBaechtel-7903 191 Reputation points

2025-06-25T00:52:25.4866667+00:00

"You failed to make all the necessary changes to reflect the various items that you renamed."

I wonder what type of changes did I fail to make?
DonBaechtel-7903 191 Reputation points

2025-06-25T00:54:22.8933333+00:00

What components from the NetServoDemo build need to be deployed with the target application?
RLWA32 49,636 Reputation points

2025-06-25T09:25:31.1966667+00:00

I wonder what type of changes did I fail to make?

You can easily see the changes I made by comparing your shared files with my updated versions for NetServerTest.idl, pGoldDLL.cs, pGoldDLL.csproj, and CppClient.cpp.

When you changed the project name from NetServerTest to pGoldDLL you also changed the name of the C# class from TestObj to pGoldDLL. The COM support for .Net projects uses the project name to form the name of the comhost dll (i.e., pGoldDLL.comhost.dll versus NetServerTest.comhost.dll). This caused your pGoldDLL project to use the wrong name for the comhost dll in several locations, including the post-build event that performs COM registration.

The C# class name is used to form the progid that will be written to the registry when the comhost dll is registered. Since the C++ client imports the type library the coclass in the idl file was conformed to reflect the changed C# class name.

When are the functions RegisterFunction and UnRegisterFunction used?

These two functions are used when the comhost dll is registered and unregistered, respectively. Since .Net COM support does not generate or register/unregister type libraries these user supplied functions provide that functionality.

What components from the NetServoDemo build need to be deployed with the target application?

After a successful build the content of the bin folder should be deployed. A release build is usually created for deployment. Generally, release builds for deployment do not include a PDB.

Answer 2

unlike the old .net framework, a .net core dll, can not be directly loaded by a C/C++ program. it needs a wrapper code. if you follow the the steps to build a COM library in .net core, you will see that a wrapper C project is created that supports loading the c# dll, and marshaling the calls.

Only windows supports com, if you want cross platform, then you probably want the C# code to expose C entry points callable from C/C++. You C/C++ code must use a net core host to load the dll.

https://learn.microsoft.com/en-us/dotnet/core/tutorials/netcore-hosting

defining methods to be callable from C/C++

https://learn.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.unmanagedcallersonlyattribute?view=net-9.0

your other option is to create a native library, which is directly callable from C/C++. this uses the AOT feature and has some restriction on supported C# code:

https://learn.microsoft.com/en-us/dotnet/core/deploying/native-aot/libraries

Answer 3

DonBaechtel-7903 191

According to the post, I added the following content to the project.cprog file

When I built the project, I encountered an error stating that the Server.tlb file could not be found.

Even though I had a Server : IServer in the source.

After adding the content, I kept getting a periodic loud BONG sound that continued until after the content was removed.

I want the Server.tlb file. How do I get it?

Attached *.csproj file:

<TargetFramework>net8.0</TargetFramework>

<ImplicitUsings>enable</ImplicitUsings>

<Nullable>enable</Nullable>

<EnableComHosting>true</EnableComHosting>

<EnableRegFreeCom>true</EnableRegFreeCom>

</PropertyGroup>

<ComHostTypeLibrary Include="Server.tlb" Id="1" />

</ItemGroup>

</Project>

DonBaechtel-7903 191 Reputation points

2025-06-17T23:29:28.5966667+00:00

Not working and generating a LOUD Bong sound in VS.
RLWA32 49,636 Reputation points

2025-06-18T00:39:52.17+00:00

The .tlb files are type libraries. They are described by IDL files that are input to the MIDL compiler which will generate the type library file.

I'll put together a small demo for you that creates a .Net 8 C# COM server and a C++ client.
RLWA32 49,636 Reputation points

2025-06-18T01:03:21.7666667+00:00

I'm not familiar with the MetaTrade5 platform. Aside from COM, another way to interoperate between native C++ and manage code is to use a C++/CLI assembly as an intermediary.

Answer 4

DonBaechtel-7903 191

Updated project at https://1drv.ms/u/c/c389bf4121acea69/EaV-4dxmGhhJrcFAnQJ1cnUB19zVLWrhWjdVWRQOee8n-g?e=U3gWn3

The project is working really well now.

Thank you very much.

Saideep Anchuri 9,500 Reputation points Moderator

2025-06-26T03:14:18.8633333+00:00

Hi DonBaechtel-7903

Glad to hear that the issue has been resolved.As an Original Poster(you) cannot accept his own answer. Can I repost your answer so that you will be able to accept the answer. Doing so will assist other community members facing similar situations in finding the right solution. Your feedback is highly valuable to us. Thank you!
RLWA32 49,636 Reputation points

2025-06-26T04:56:33.8533333+00:00

@DonBaechtel-7903, I'm happy that all of our work together got you to where you wanted to be.I'd appreciate it if you would accept my posted Answer to close this thread.

Answer 5

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Error trying to call a C# DLL from a C++ console app

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