Hi,
So I tried it out, and there're a couple of things:
- Declaring a function as `static` will hide it from anything other than the current translation unit, AFAIK, which means that you won't be able to link it to anything else; the symbol won't be visible (you can verify using `objdump`).
- For C++ functions, you need to suppress name-mangling since Haskell's FFI doesn't know about that. With your repo as is, the symbol corresponding to the `multiply` function is not...`multiply`:
```
dist-newstyle/build/x86_64-linux/ghc-8.6.5/HaskellForeignCPP-0.0.1/build/cpp-src/some.o: file format elf64-x86-64
SYMBOL TABLE:
0000000000000000 l df *ABS* 0000000000000000 some.cpp
0000000000000000 l d .text 0000000000000000 .text
0000000000000000 l d .data 0000000000000000 .data
0000000000000000 l d .bss 0000000000000000 .bss
0000000000000000 l d .note.GNU-stack 0000000000000000 .note.GNU-stack
0000000000000000 l d .eh_frame 0000000000000000 .eh_frame
0000000000000000 l d .comment 0000000000000000 .comment
0000000000000000 g F .text 0000000000000006 _Z8multiplyii```
With `extern "C"` and removing `static`:
```
dist-newstyle/build/x86_64-linux/ghc-8.6.5/HaskellForeignCPP-0.0.1/build/cpp-src/some.o: file format elf64-x86-64
SYMBOL TABLE:
0000000000000000 l df *ABS* 0000000000000000 some.cpp
0000000000000000 l d .text 0000000000000000 .text
0000000000000000 l d .data 0000000000000000 .data
0000000000000000 l d .bss 0000000000000000 .bss
0000000000000000 l d .note.GNU-stack 0000000000000000 .note.GNU-stack
0000000000000000 l d .eh_frame 0000000000000000 .eh_frame
0000000000000000 l d .comment 0000000000000000 .comment
0000000000000000 g F .text 0000000000000006 multiply
```
...and everything builds fine.
Best,
toz
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Today's Topics:
1. Re: Linking C++ in Cabal - repository Link (Leonhard Applis)
2. Re: Linking C++ in Cabal (鲍凯文)
----------------------------------------------------------------------
Message: 1
Date: Mon, 25 May 2020 13:00:03 +0000
From: Leonhard Applis <Leonhard.Applis@protonmail.com>
To: "beginners@haskell.org" <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Linking C++ in Cabal - repository
Link
Message-ID:
<iF7eLvkM4HniAVDyO09U-O3y48pPEAciKs5zjKAtajj8lldf1g8Tp5UHi3-HiT2GMc15GBi5JgVgkRXr4KQ8Y8p6i0CuuAU-RLh-g2t57uQ=@protonmail.com>
Content-Type: text/plain; charset="utf-8"
Ups, in my mailing list the links have disappeared.
Just in case:
The minimal reproducing repository:
https://github.com/Twonki/HaskellForeingCPPMinimal
The repository from Aditya Siram with C and makefile:
https://github.com/deech/CPlusPlusBindings
best
Leonhard
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Monday, May 25, 2020 2:00 PM, <beginners-request@haskell.org> wrote:
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> Today's Topics:
>
> 1. Linking C++ in Cabal (Leonhard Applis)
>
>
> Message: 1
> Date: Sun, 24 May 2020 16:30:22 +0000
> From: Leonhard Applis Leonhard.Applis@protonmail.com
> To: "beginners@haskell.org" beginners@haskell.org
> Subject: [Haskell-beginners] Linking C++ in Cabal
> Message-ID:
> 51wOfngyX74dYjJRw6hibqw07vGHvvSYPD_f3f2-_F7hG0k0GwWf2Xv4g7LyeZNyn_vR28s6GIbd3e-78_TapNIEo_tJZ-2fTViOmkQYOnM=@protonmail.com
>
> Content-Type: text/plain; charset="utf-8"
>
> Hello,
>
> I want to use a foreign C++ Function in a Haskell Library, and the Library in a Haskell Program.
> The C++ function is separate in a file and I have a header file.
> I made a minimal reproducing repository.
>
> The closes I have found is this repository which wraps the c++ in c and makes a full library, needing a makefile etc.
> So while I think I'd get it working like that, it looks to be quite a lot to do for my simple task.
>
> the repository structure looks as follows:
>
> Projekt
>
> - cpp-src
> - some.cpp
> - some.h
> - lib-src
> - CPPLib.hs
> - program-src
> - program.hs
> - project.cabal
>
> And my (currently failing) project.cabal the following:
>
> cabal-version: 3.0
> name: cpp_lib
> [...]
> library
> exposed-modules: CPPLib
> other-extensions: ForeignFunctionInterface
> build-depends: base
> hs-source-dirs: lib-src
> default-language: Haskell2010
> include-dirs: ./cpp-src
> cxx-sources: ./cpp-src/some.cpp
> install-includes: ./cpp-src/some.h
>
> executable CPPApp
> main-is: program.hs
> default-language: Haskell2010
> build-depends: HaskellForeignCPP,
> base
> hs-source-dirs: program-src
>
> The some.cpp is trivial for this case lets assume its a function multiply :: Int -> Int -> Int, and both .cpp and .h are well-formed and don't have further dependencies.
>
>
> The library compiles fine, but when building the executable it fails telling me
>
> collect2: error: ld returned 1 exit status
> `gcc' failed in phase`Linker'. (Exit code: 1)
>
> Can someone help me out?
> I find very little documentation on this topic.
>
> I know there is Inline-CPP which would help as well, but I just very much like the idea of having a nice separate file and interface for modularity.
>
> best
> Leonhard
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------------------------------
Message: 2
Date: Mon, 25 May 2020 16:45:09 -0700
From: 鲍凯文 <traqueofziche@gmail.com>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] Linking C++ in Cabal
Message-ID:
<CAMjcG+FWPZtkM7soC34VOdSBQ+ArdWY2Bpk2Wm=XNqEdg3ox2Q@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
Would it be possible to upload your full repo somewhere so people could see
everything and possibly reproduce this?
Thanks,
toz
On Mon, May 25, 2020 at 5:03 AM <beginners-request@haskell.org> wrote:
> Send Beginners mailing list submissions to
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> Today's Topics:
>
> 1. Linking C++ in Cabal (Leonhard Applis)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 24 May 2020 16:30:22 +0000
> From: Leonhard Applis <Leonhard.Applis@protonmail.com>
> To: "beginners@haskell.org" <beginners@haskell.org>
> Subject: [Haskell-beginners] Linking C++ in Cabal
> Message-ID:
>
> <51wOfngyX74dYjJRw6hibqw07vGHvvSYPD_f3f2-_F7hG0k0GwWf2Xv4g7LyeZNyn_vR28s6GIbd3e-78_TapNIEo_tJZ-2fTViOmkQYOnM=@
> protonmail.com>
>
> Content-Type: text/plain; charset="utf-8"
>
> Hello,
>
> I want to use a foreign C++ Function in a Haskell Library, and the Library
> in a Haskell Program.
> The C++ function is separate in a file and I have a header file.
> I made a minimal reproducing repository.
>
> The closes I have found is this repository which wraps the c++ in c and
> makes a full library, needing a makefile etc.
> So while I think I'd get it working like that, it looks to be quite a lot
> to do for my simple task.
>
> the repository structure looks as follows:
>
> Projekt
>
> - cpp-src
>
> - some.cpp
> - some.h
>
> - lib-src
>
> - CPPLib.hs
>
> - program-src
>
> - program.hs
>
> - project.cabal
>
>
>
> And my (currently failing) project.cabal the following:
>
> cabal-version: 3.0
> name: cpp_lib
> [...]
> library
> exposed-modules: CPPLib
> other-extensions: ForeignFunctionInterface
> build-depends: base
> hs-source-dirs: lib-src
> default-language: Haskell2010
> include-dirs: ./cpp-src
> cxx-sources: ./cpp-src/some.cpp
> install-includes: ./cpp-src/some.h
>
> executable CPPApp
> main-is: program.hs
> default-language: Haskell2010
> build-depends: HaskellForeignCPP,
> base
> hs-source-dirs: program-src
>
> The some.cpp is trivial for this case lets assume its a function multiply
> :: Int -> Int -> Int, and both .cpp and .h are well-formed and don't have
> further dependencies.
>
> The library compiles fine, but when building the executable it fails
> telling me
>
> collect2: error: ld returned 1 exit status
> `gcc' failed in phase `Linker'. (Exit code: 1)
>
> Can someone help me out?
> I find very little documentation on this topic.
>
> I know there is Inline-CPP which would help as well, but I just very much
> like the idea of having a nice separate file and interface for modularity.
>
> best
> Leonhard
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