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VC++ Interop DLL: Binary was not built with debug information

I have a VC++ (.exe) application built in Visual Studio 2019. In project properties I have set to generate debug information for it.
Configuration Properties --> C/C++ --> Debug information format --> Program Database for Edit and Continue (/ZI)
Configuration Properties --> Linker --> Debugging --> Generate Debug Info --> Generate Debug Information (/DEBUG) (Also I have tried here: Generate Debug Information optimized for sharing and publishing (/DEBUG:FULL)
In the output it generates three files:
myApp.exe
myApp.pdb
myApp.Interop.dll
Now from another C# app I launched this VC++ exe app by using Process.Start("myapp.exe") in order to communicate between them later.
Now I am trying to debug C# and VC++ apps so I open two instances of VS, one for each app.
From VS I start debugging the C# app and from the another VS I attach to the process VC++ app. In the VS where I have launched my C# app, in modules window I can see below message:
C:\Users\myUser\AppData\Local\assembly\dl3\C23J1LN6.XOZ\GJPNWB74.YC1\bdcce8ba\10fb0e7d_e918d801\myApp.Interop.dll --> Binary was not built with debug information
Why isn't it capable to find my myApp.pdb file that was generated? all myApp.* are in the same directory.

It looks like an issue with the debugger type that you are using in the solution with the C# project. Visual Studio will default to "Managed only" when debugging a C# project. However, you want to debug both the C# project and the associated C++ dll. When trying to load the symbols for a native application / shared library it will fail as if there were no valid symbols.
Depending on how you attach to the C# executable:
if you are starting the executable directly from Visual Studio, you need to check "Enable native code debugging" in the Debug tab of your project properties [1];
if you are starting the executable externally and only later attaching using Visual Studio, you need to select "Native" and "Managed" clicking on the Select button in the "Attach to" row.
References
[1] https://learn.microsoft.com/en-us/visualstudio/debugger/how-to-debug-managed-and-native-code#configure-mixed-mode-debugging
[2] https://learn.microsoft.com/en-us/visualstudio/debugger/how-to-debug-in-mixed-mode

How do I add debug unmanaged C++ project vs2010 called by a C# project in vs2017?

I have an un-managed WIN32 dll that was written in VC++ 6 and called from a C# application. I have the dll project in VS2010 and C# project in VS2017. Both project can run through under debug/release mode successfully.
I found there was something wrong with the arguments passed by C# to the dll and thus wanted to debug the dll project. Here is what I did.
Open both VS2010 dll and VS2017 C# project
Change both projects' debugger type to mixed.
Change both projects' property to enable un-managed code debugging (it's called native code in VS2017)
Set break points at the argument calculation inside the dll where I want to debug and the C## function where I called the dll
For both vs2017 and vs2010, under Tools>Options>Debugging>Symbols I define the path where .pdb files were generated for the dll project and Select "Automatically load symbols for all modules"
Start debugging C# code
In VS2010 C++ Project, select attach to process to attach the project to vs2017 exe; under select I chose both "managed" and "native"
The breakpoint of my c++ code showed as invalid since"no symbols have been loaded for this document"
I have been struggling with this problem for a long time. Any suggestion would be really appreciated!

"skipped loading symbols for ngen binary" for C# dll

I'm trying to debug a C# dll from a native C++ executable. I have a C# COM object that is loaded and run from native code via IDispatch. Everything is built in Debug, both C# and C++ code. Whilst I can see all the c++ code, and all the c++ dlls have their symbols loaded and available for debugging, breakpoints etc the C# code refuses to play.
What I do see is that the C# dlls all refuse to load their symbol pdbs, reporting "skipped loading symbols for ngen binary" in the modules window.
Incidentally, I am debugging the C# solution here, I have set the native executable as the 'start external program' in the COM project's debug settings.
Now I can start the C++ executable and then attach to it, and then all works as I expect - the symbols load and I can set breakpoints in the C#.
This is using Visual Studio 2013u4. Is there a setting to enable mixed-mode debugging? One niggle is that the native code was built with VS2010.
Here's the Module window - note all pdbs and dlls are in a single directory, you can see the c++ dlls loaded, but not the C# ones.
Here's the modules window - note the 3rd entry for the EvCom dll (the COM object) which I assume is the entry enabling debugging.
There is nothing of any interest in the Output window, when it comes to load the COM dll, I see the following (in the case of attach to running process, the other only has 2 Loaded lines instead of 3).
'Explorer.exe' (Win32): Loaded 'C:\Dev\...\lib\debug\EvCom.dll'.
'Explorer.exe' (Win32): Loaded 'C:\Dev\...\lib\debug\EvCom.dll'.
'Explorer.exe' (Win32): Unloaded 'C:\...\lib\debug\EvCom.dll'
'Explorer.exe' (Win32): Loaded 'C:\Dev\...\lib\debug\EvCom.dll'.
One thing of interest - I checked the "Use Managed Compatibility Mode" in the debug settings and, thought it still doesn't load my symbols when starting debugging, it only shows 1 entry in the modules list. This time saying "No native symbols in symbol file" for the C# dlls.
It looks like the problem is not being able to select the debugger type in VS2013 (or 2012). This connect article suggests its "by design" with some workarounds.

Turns out it is all down to the changes in debug engine for .NET 4.0
.NET 4 and greater uses a different debug engine than .net 3.5 and below, when you start debugging a native application the debugger will choose a .net debugger for you (defaults to .net 4.0) and if your .net dll is built using this platform, all will be well - breakpoints will be hit.
If your loaded dll is .net 3.5, then the debug engine will not understand the dlls that are loaded and will refuse to load symbols or debug.
The solutions are either to rebuild as .net 4, or start the native executable and attach to it (where you can select the debugger type, either 'old' .net or 'new' .net) or you can create a project from the executable and set its debug settings to specify the right debugger.
What I find annoying is that Microsoft could easily have started the debugger using the .NET framework type specified in the project you're debugging (after all, when debugging a dll and specifying an external program, you still want to debug the dll you're pressing F5 for, so you know what debugger to use!)(What is even more annoying is that once managed debugging is started in a loaded dll, you can then step into projects built using older .net frameworks without problem).
More details on this Microsoft connect article

(If your executable isn't already in your solution, File > Add > Existing project, then right-click and set it as start-up project.)
Right-click your start-up project, Properties, Debugging, Debugger Type = Mixed.

In my case I have own symbol server and TFS, so I
enabled option TOOLS > Options > Debugging > General > "Enable source server support" and three child options.

For me is was debugging a UWP app in Xamarin Forms:
Cause:
The debugger is skipping files not in the .NET environment.
Solution:
Uncheck Debugging => General => Enable Just My Code

How to debug the c++ dll from c# project?

I have created a visual c++ 6.0 dll project and using it from my c# code. Now i want to debug the dll but i am not able to do it.
I choose the following option to do it:
put the breaking point in my visual c++ project code.
build the dll and copy it into the directory of my c# project.
Now i build my c# project and dll works fine (method are calling perfectly).
Now i want to debug the dll.
I follow a blog and open the c++ project and choose the Attach to process from vc++.
but i am not able to find the running process of visual c# project, whereas it available at task manager process.
In my c# project solution i have two project i.e.
web service (i called the dll method at the time of accessing a url)
Another one is webform application which starts the web services.
Now please help me how should i debug my dll. I have followed so many blogs but all of them are focusing on Attaching process method which is not working in my condition. What should i do?

You'll need to enable unmanaged debugging, it is not turned on by default in either scenario because your main program is managed.
You do it in your C# project with Project > Properties > Debug tab > tick the "Enable unmanaged code debugging" checkbox.
You do it with Tools > Attach to Process by clicking the Select button. Choose the "Debug these code types" radio button and tick both Managed and Native. You may have to resort to only native if your process is 64-bit.
Set a breakpoint in the DLL's source code and be sure to write C# code that exercises the DLL function. If you still have trouble getting a breakpoint then use Debug > Windows > Modules and verify that you see the DLL in the module list. Get additional troubleshooting info by right-clicking it, select Symbol Load Information. Which shows a trace of where the debugger looked for the PDB file.

You can add C++ project to the your C# solution and add reference directly to the project (not dll), then you will not be needing to copy DLL. After that just start normal debugging (F5) of your C# project, and breakpoints will be working for C++ project too. This way will be very comfortable for debugging. I have tried such debugging and did not change any other settings.

Debug C# dll from C++ solution via COM

I have a C++ solution. The startup project is an exe. In the solution there are a number C# dlls (targeting .NET Framework 2.0) that are registered for COM interop. When I put a breakpoint in the C# code I get the hollow red breakpoint with "No native symbols in symbol file"
I have tried setting Project Property Pages -> Debugging -> Debugger Type to Mixed on the start-up project that calls the COM methods.
I have checked Debug -> Windows -> Modules. It has loaded my dlls, and the symbol status is "No native symbols in symbol file".
This is not the end of the world because if I do Debug -> Start Without Debugging and then Debug -> Attach to Process, changing the Attach To: to Managed (v2.0, v1.1, v1.0) code, Native code. Then I hit breakpoints in both the C++ code and C# code.
So I have my workaround but I reckon if I can do it by attaching to process - I should be able to do it by just debugging.
How can I hit my C# breakpoints by just doing Debug -> Start Debugging?

I was able to debug my C# dll from a C++ project in VS2008 by doing the following:
In the C++ project's properties, goto Configuration Properties -> Debugging. Set "Debugger Type" to Mixed. "Attach" should be set to No.
In your C# project properties, in the Debug tab, set the "Start External Program" to your C++ project's executable.

I know it's a little bit old but I found a practical solution for the problem.
I had the same problem while using a C++ application which uses a C# COM-Object. I tried several settings within Visual Studio on the C++ and C# side. Nothing helps until I tried manually launching the Debugger.
You can use
Debugger.Launch();
to manually start the Debugger on your C# DLL. I know this is not the best but a practical way. In later productive environments you have to remove the Debugger launch function :).
Regards

I am unsure if this will help but we work a lot with C# and C++. I found this to be possible by placing the C++ project and the C# project in the same solution and enabling "native debugging" in the C# project. Then I was able to jump back and forth between them while debugging.