DllExport | NET DllExport with .NET Core support

This usage of restrict doesn't make much sense. The keyword only serves a purpose when you have two or more pointers to compatible types and the compiler can't know if they potentially point at the same object. Or if they possibly point to an object with external linkage ("global") in the same translation unit. More details here.

In funcA the pointer has no relation to any other pointer or object in the program, since it is assigned to dynamic memory inside the function. restrict fills no obvious purpose at all in that function.

This is something I noticed:

Don't export functions from EXEs. Export a function from the DLL that accepts a function pointer as input, then have the EXE call that function at runtime.

EXE:

Your approach is correct but your program contains some undefined symbols which need to be imported from libstdc++ at startup (e.g. std::cout). Linker has to insert such symbols in your library's symbol table, otherwise loader won't know that they need to be imported.

You can link against static version of STL (via -static-libstdc++) and apply a version script to prevent linker from exporting STL symbols from your shared library:

The function is returning a char**, and you've told Python that it is returning a char*[3] (an array of 3 char* pointers, not a pointer itself), so the returned value isn't being interpreted properly by ctypes.

Change the return type to ctypes.POINTER(ctypes.c_char_p), or alternatively change your program to return something that has the same size as char*[3], like std::array or struct otp_data { char *one, *two, *three; }; (which would be 1 less malloc since you can return this by value)

I've found a solution. Knowing that it was not tied to numpy halped quite a lot to switch the focus on the real problem: symbol missing. Taking the suggestion from this answer and in particular this point:

Solve a problem. Load the library found in step 1 by dlopen first (use RTLD_GLOBAL there as well).

I've modified the minimum example as follows:

I believe it's fixed. I'm finally able to see exported functions in the dumpbin /exports output. There were several things that I believe needed to be done to correct the problem. Hope this helps someone in the future.

Packaged is Not Updated - Try Older Version of VS

Based on the age of the package I suspected it wasn't cooperating in VS2022 so, I:

• Created the project in Visual Studio 2015 (vs VS2022 which I was using)
• Rebuilt project from scratch and added references to new project rather than trying to open old project in VS2015

DllExportAppDomainIsolatedTask Error

Then, the project wouldn't build, it kept throwing the error:

The "DllExportAppDomainIsolatedTask" task failed unexpectedly.

Based on this answer I:

• Installed Microsoft Build Tools for VS2015
• Installed .NET 3.5 and manually added Microsoft.Build.Tasks.v3.5 as a reference to my project by browsing to its location after the .NET3.5 install

But I kept receiving the same error. I then increased the debug output by changing the setting: Project>Properties>Build>Errors and Warnings>Warning Level to 4.

Digging through the debug log I found several lines from the UnmanagedExports package which referenced the project platform, framework path, library tools path, tools dll path, etc. In that section I found: System.ArgumentException: Requested value 'Version47' was not found.

I was targeting .NET Framework 4.7.2 so I downgraded the project to target .NET Framework 4.5, deleted the bin/obj folder contents and rebuilt the project. Then, running dumpbin /exports showed my HelloWorld function!

It doesn't appear the package is compatible with .NET Framework 4.7.2.

After deep research, I found out how to call from C# to the C DLL.

The C# code should be:

Do I have to add my macro (MY_API) to the B class?

If that B class is also exported/imported (which, presumably, it is), then: Yes, you do.

Try the following code, where we are building the DLL and exporting the classes: