I would like to export some functions from my bettec dll for dotnet core application in windows.

Right now I have compiled dll using dmd v2.091.0-dirty simply by ´dub build´

this is the function I have

extern(C) char* test_echo(const(char)* line, size_t len,  ref size_t resLen)
{
    enum format = "{\"message\": \"%s\"}\n";

    auto response = cast(char*)malloc(format.length + len);
    resLen = sprintf(response, format, line);
    return response;
}

and this is my dotnet core equivalent

[DllImport(DllName, CallingConvention = CallingConvention.StdCall)]
static extern IntPtr test_echo([MarshalAs(UnmanagedType.LPStr)]string line, ulong len, out ulong resLen);

This works for me in linux but does not in windows, any idea what I'm doing wrong?

This is the output from dotnet core

Unhandled exception. System.EntryPointNotFoundException: Unable to find an entry point named 'test_echo' in DLL 'test.dll'

On Saturday, 14 March 2020 at 20:53:45 UTC, Abby wrote:
> I would like to export some functions from my bettec dll for dotnet core application in windows.
>
> [...]

It is the calling convention.

On Saturday, 14 March 2020 at 20:53:45 UTC, Abby wrote:
> I would like to export some functions from my bettec dll for dotnet core application in windows.
>
> Right now I have compiled dll using dmd v2.091.0-dirty simply by ´dub build´
>
> this is the function I have
>
> extern(C) char* test_echo(const(char)* line, size_t len,  ref size_t resLen)
> {
>     enum format = "{\"message\": \"%s\"}\n";
>
>     auto response = cast(char*)malloc(format.length + len);
>     resLen = sprintf(response, format, line);
>     return response;
> }
>
> and this is my dotnet core equivalent
>
> [DllImport(DllName, CallingConvention = CallingConvention.StdCall)]
> static extern IntPtr test_echo([MarshalAs(UnmanagedType.LPStr)]string line, ulong len, out ulong resLen);
>
> This works for me in linux but does not in windows, any idea what I'm doing wrong?

For one thing, you're defining it with stdcall in dotnet, but cdecl in the code. You should change the convention on the dotnet side to CallingConvention.Cdecl. Or, if you really want to use stdcall, use extern(System) in D -- the equivalent of extern(Windows) on Windows and extern(C) everywhere else.

Also, I would expect you'd have to use export [1] on the D side for the symbol to be loadable from the dll:

extern(C) export char* test_echo(...) { ... }

This should be the equivalent of __declspec(dllexport) for C and C++ on Windows.

[1] https://dlang.org/spec/attribute.html#visibility_attributes (Item #7)

On Saturday, 14 March 2020 at 20:53:45 UTC, Abby wrote:
> I would like to export some functions from my bettec dll for dotnet core application in windows.


You can check my library documentation to understand how to do some fancy interop between C# and D: https://github.com/ahmetsait/IDL/wiki

Should probably write a detailed blog post about that some time :/