Thanks Toz!
Works like a charm.
Repository is updated for anyone interested.
Beginners Mailing list is the best <3
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, May 26, 2020 10:01 PM,
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1. Re: Linking C++ in Cabal (鲍凯文)
Message: 1 Date: Tue, 26 May 2020 13:03:13 -0700 From: 鲍凯文 traqueofziche@gmail.com To: beginners@haskell.org Subject: Re: [Haskell-beginners] Linking C++ in Cabal Message-ID: CAMjcG+FisqcazdRV14Hut7QS1-37tyhXptZG2prNH7-90aswmA@mail.gmail.com Content-Type: text/plain; charset="utf-8"
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
so you just need to wrap every exposed function in `extern "C"` blocks, like it's explained here: https://www.geeksforgeeks.org/extern-c-in-c/.
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
On Tue, May 26, 2020 at 5:03 AM beginners-request@haskell.org wrote:
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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:
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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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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Leonhard Applis