我正在嘗試使用 FFI 系結到 Haskell 中的 C 庫，但我收到“缺少（或壞的）C 庫”。
我在 Ubuntu Linux 上使用 Haskell Tool Stack 2.7.3。我做了一個最小的可重復示例如下。
這是我運行時的錯誤訊息stack build：
Building all executables for `c' once. After a successful build of all of them, only specified executables will be rebuilt.
c> configure (lib exe)
Configuring c-0.0.0...
Cabal-simple_mPHDZzAJ_3.2.1.0_ghc-8.10.7: Missing dependency on a foreign
library:
* Missing (or bad) C library: small
This problem can usually be solved by installing the system package that
provides this library (you may need the "-dev" version). If the library is
already installed but in a non-standard location then you can use the flags
--extra-include-dirs= and --extra-lib-dirs= to specify where it is.If the
library file does exist, it may contain errors that are caught by the C
compiler at the preprocessing stage. In this case you can re-run configure
with the verbosity flag -v3 to see the error messages.
-- While building package c-0.0.0 (scroll up to its section to see the error) using:
/home/t/.stack/setup-exe-cache/x86_64-linux-tinfo6/Cabal-simple_mPHDZzAJ_3.2.1.0_ghc-8.10.7 --builddir=.stack-work/dist/x86_64-linux-tinfo6/Cabal-3.2.1.0 configure --user --package-db=clear --package-db=global --package-db=/home/t/.stack/snapshots/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/pkgdb --package-db=/home/t/c/.stack-work/install/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/pkgdb --libdir=/home/t/c/.stack-work/install/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/lib --bindir=/home/t/c/.stack-work/install/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/bin --datadir=/home/t/c/.stack-work/install/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/share --libexecdir=/home/t/c/.stack-work/install/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/libexec --sysconfdir=/home/t/c/.stack-work/install/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/etc --docdir=/home/t/c/.stack-work/install/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/doc/c-0.0.0 --htmldir=/home/t/c/.stack-work/install/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/doc/c-0.0.0 --haddockdir=/home/t/c/.stack-work/install/x86_64-linux-tinfo6/789c3ce353623de67e3141c688e7a5c70e1e6d9a517056f87d6850c406d11f12/8.10.7/doc/c-0.0.0 --dependency=base=base-4.14.3.0 --extra-include-dirs=/home/t/c/src --extra-lib-dirs=/home/t/c/src --exact-configuration --ghc-option=-fhide-source-paths
Process exited with code: ExitFailure 1
我的package.yaml檔案：
name: c
dependencies:
- base >= 4.7 && < 5
library:
source-dirs: src
extra-libraries: small
executables:
c-exe:
main: Main.hs
source-dirs: app
ghc-options:
- -threaded
- -rtsopts
- -with-rtsopts=-N
dependencies:
- c
src/Lib.hs包含系結的檔案：
{-# LANGUAGE ForeignFunctionInterface #-}
{-# LANGUAGE CApiFFI #-}
module Lib
( x
) where
import qualified Foreign.C.Types as F
foreign import capi "small.h x" x :: IO F.CInt
該src/small.c檔案：
#include "small.h"
int x() {
return 0;
}
該src/small.h檔案：
int x();
我C首先編譯了代碼：
gcc -c -o src/small.o src/small.c
我的stack.yaml檔案：
resolver:
url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/18/20.yaml
extra-include-dirs:
- src
extra-lib-dirs:
- src
為了方便起見，我把這個最小的例子放在 Github 上：
git clone https://github.com/8n8/haskell-c-ffi-minimal
cd haskell-c-ffi-minimal
stack build
uj5u.com熱心網友回復：
在package.yaml檔案的library部分中，將其更改為
library:
source-dirs: src
c-sources:
- src/small.c
并且stack.yaml檔案可以減少到
resolver:
url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/18/20.yaml
并且無需執行單獨的步驟來編譯C代碼。
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