c - C2HS 生成的 C 绑定(bind)中的链接器错误

Question

我构建并运行了以下最小示例(无外部依赖项) C->Haskell Compiler, version 0.25.2 Snowboundest, 31 Oct 2014
build platform is "x86_64-darwin" <1, True, True, 1> ;构建命令:

c2hs Structs.chs
ghci Structs.hs

但是链接器提示

During interactive linking, GHCi couldn't find the following symbol: get_foo

问:为什么会这样，我该如何解决？提前致谢

答:tl;dr:我没有将 .c 编译成 .o 目标代码，DUH!

代码如下:

Structs.chs

module Main where

import Foreign
import Foreign.C

#include "Structs.h"

{#pointer *foo as Foo#}

{#fun get_foo {`Int'} -> `Foo' return* #}

main :: IO ()
main = do
  foo <- get_foo 3
  a1 <- {#get struct foo->a#} foo
  print a1

Structs.h

struct foo {
  int a;
};

struct foo *get_foo(int n);

Structs.c

#include "Structs.h"

struct foo f;

struct foo *get_foo(int n)
{
  f.a = n;
  return &f;
}

Structs.hs

-- -- C2HS generated Hs file, edited for clarity
module Main where

import Foreign
import Foreign.C

type Foo = Ptr ()

get_foo :: Int -> IO Foo
get_foo p =
  get_foo'_ (fromIntegral p)

main :: IO ()
main = do
  foo <- get_foo 3
  a1 <- (\ptr -> peekByteOff ptr 0 :: IO CInt) foo
  print a1

foreign import ccall safe "Structs.chs.h get_foo"
  get_foo'_ :: CInt -> IO Foo

编辑:ghc --make Structs.hs给出相同的链接器错误:

$ ghc --make Structs.hs
Linking Structs1a ...
Undefined symbols for architecture x86_64:
"_get_foo", referenced from:
    _c2MX_info in Structs.o
    _c2Or_info in Structs.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

get_foo C 函数在 Structs.c 中定义，因此您需要让 GHC 可以使用它。这应该有效:

gcc -o Structs_c.o -c Structs.c
ghc --make Structs.hs Structs_c.o

对于 GHCi，我认为您可以说 ghci Structs.hs Structs_c.o。但是您肯定需要 C 目标文件!