I'm having a little bit of problem calling D code from C++ and would appreciate some assistance. First, given the following C++ program wich compiles, links, and runs without any problem:

    ======================
    // example.h
    SOME_API void foo(const char* str);

    // example.cpp
    #include "example.h"
    namespace SomeApi {}
    struct SomeStruct {}
    int main() {
        foo("do great things");
        return 0;
    }
    void foo(const char* str) {
        // doing great things;
    }
    ======================

Modify example.cpp to:

    ======================
    // example.cpp
    #include "example.h"
    namespace SomeApi {}
    struct SomeStruct {}
    void call_cpp() {
        foo("do great things");
        return;
    }
    ======================

Then create example.d:

    ======================
    void main() {
        call_cpp();
    }

    extern (C++) void foo(const char* str) {
        // doing great things;
    }
    ======================

Compile and link and you have D program calling, calling C++, which in turn calls D.

My problem is that I've encountered an issue where this does not work: when the function is being called from a namespace or local scope in C++, the linker cannot find the definition. For example:

    void SomeApi::CallFromNamespace() {
        foo("do great things");
    }

or
    void SomeStruct::CallFromStruct() {
        foo("do great things");
    }

In a last-ditch effort, I placed all of these definitions into dexample.d and, it compiled, but still filed to linking:

    extern (C) void foo(const char* str) {
        // doing great things;
    }

    extern (C++) void foo(const char* str) {
        // doing great things;
    }

    extern (C++, SOME_API) void foo(const char* str) {
        // doing great things;
    }

    extern (D) void foo(const char* str) {
        // doing great things;
    }

    extern void foo(const char* str) {
        // doing great things;
    }

    void foo(const char* str) {
        // doing great things;
    }

===============
Linker error returned:
===============

Undefined symbols for architecture x86_64:
  "foo()", referenced from:
      SomeStruct::CallFromStruct() in example.o
      SomeApi::CallFromNamespace() in example.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [dexample] Error 1

Using DMD v2.077.0 on macOS High Sierra

-Andrew

On Wednesday, 8 November 2017 at 06:34:27 UTC, Andrew Edwards wrote:
> I'm having a little bit of problem calling D code from C++ and would appreciate some assistance. First, given the following C++ program wich compiles, links, and runs without any problem:

Try using `nm` on the C++ object to find out what it thinks the mangling should be.
Check that against the mangling DMD produces.

On Wednesday, 8 November 2017 at 06:34:27 UTC, Andrew Edwards wrote:
>
> Modify example.cpp to:
>
>     ======================
>     // example.cpp
>     #include "example.h"
>     namespace SomeApi {}
>     struct SomeStruct {}
>     void call_cpp() {
>         foo("do great things");
>         return;
>     }
>     ======================

>
> Compile and link and you have D program calling, calling C++, which in turn calls D.
>
> My problem is that I've encountered an issue where this does not work: when the function is being called from a namespace or local scope in C++, the linker cannot find the definition. For example:
>

just using fully qualified name didn't make it?

void call_cpp() {
    ::foo("do great things"); // calling global foo
    return;
}

>
> In a last-ditch effort, I placed all of these definitions into dexample.d and, it compiled, but still filed to linking:
>

Are you sure you put it in a namespace in C++ too?

otherwise there might be some name mangling incompatibility that probably worth filling a bug report

On Wednesday, 8 November 2017 at 07:06:39 UTC, Nicholas Wilson wrote:
> On Wednesday, 8 November 2017 at 06:34:27 UTC, Andrew Edwards wrote:
>> I'm having a little bit of problem calling D code from C++ and would appreciate some assistance. First, given the following C++ program wich compiles, links, and runs without any problem:
>
> Try using `nm` on the C++ object to find out what it thinks the mangling should be.
> Check that against the mangling DMD produces.

Tried it, and it works.

Solution:

    nm dexample | grep foo -> returns the __C++__mangling

Use it to define the function as such:

    pragma(mangle, "__C++__mangling")
    extern (C++) void foo(const char* str) {
        // doing great things;
    }

Thank you so much.

-Andrew

On Wednesday, 8 November 2017 at 07:30:34 UTC, evilrat wrote:
> On Wednesday, 8 November 2017 at 06:34:27 UTC, Andrew Edwards
>
> just using fully qualified name didn't make it?
>
> void call_cpp() {
>     ::foo("do great things"); // calling global foo
>     return;
> }
>

No, it did not.

> Are you sure you put it in a namespace in C++ too?

Yes. That wasn't the issue

> otherwise there might be some name mangling incompatibility that probably worth filling a bug report

That's the one. Thanks to the hint form, Nicholas Wilson, I was able to track it down and resolve it with a call to pragma(mangle).

-Andrew

On Wednesday, 8 November 2017 at 07:55:02 UTC, Andrew Edwards wrote:
> On Wednesday, 8 November 2017 at 07:30:34 UTC, evilrat wrote:
>> On Wednesday, 8 November 2017 at 06:34:27 UTC, Andrew Edwards
>>
>> just using fully qualified name didn't make it?
>>
>> void call_cpp() {
>>     ::foo("do great things"); // calling global foo
>>     return;
>> }
>>
>
> No, it did not.
>
>> Are you sure you put it in a namespace in C++ too?
>
> Yes. That wasn't the issue
>
>> otherwise there might be some name mangling incompatibility that probably worth filling a bug report
>
> That's the one. Thanks to the hint form, Nicholas Wilson, I was able to track it down and resolve it with a call to pragma(mangle).
>
> -Andrew

Walter has recently been working on improving the C++ mangling, so be sure to test the latest dmd nightly build and if that doesn't work be sure to file bug report(s).

https://github.com/dlang/dmd/pull/7250
https://github.com/dlang/dmd/pull/7259
https://github.com/dlang/dmd/pull/7272

On Wednesday, 8 November 2017 at 06:34:27 UTC, Andrew Edwards wrote:
> I'm having a little bit of problem calling D code from C++ and would appreciate some assistance. First, given the following C++ program wich compiles, links, and runs without any problem:

The useful material.
https://www.youtube.com/watch?v=HTgJaRRfLPk

On Wednesday, 8 November 2017 at 15:12:05 UTC, MGW wrote:
> The useful material.
> https://www.youtube.com/watch?v=HTgJaRRfLPk

Useful indeed, thank you.

On Wednesday, 8 November 2017 at 08:42:01 UTC, Petar Kirov [ZombineDev] wrote:
>
> Walter has recently been working on improving the C++ mangling, so be sure to test the latest dmd nightly build and if that doesn't work be sure to file bug report(s).
>
> https://github.com/dlang/dmd/pull/7250
> https://github.com/dlang/dmd/pull/7259
> https://github.com/dlang/dmd/pull/7272

Done: https://issues.dlang.org/show_bug.cgi?id=17975