我正在尝试编写一个与C通信的Haskell程序(最终通过GHC-iOS为iOS)。我想让它从C传递一个字符串到Haskell,让Haskell处理它,然后通过hsc2s将一些数据类型从Haskell返回到C Structs。我找不到一个简单明了的教程是不成功的。 Haskell唯一需要的是String,没有别的。
我对第一部分没有任何问题,将字符串传递给Haskell。
testPrint :: CString -> IO ()
testPrint c = do
s <- peekCString c
putStrLn s
出于测试目的和将来的参考,我只希望能够处理以下内容。
C Struct
struct testdata {
char *a;
char *b;
int c;
};
Haskell数据类型
data TestData = TestData {
a :: String,
b :: String,
c :: Int
} deriving Show
-- not sure what the type would look like
testParse :: CString -> TestData
我知道我需要将TestData类型化为Storable并实现peek,poke,sizeOf和alignment,但我需要先看一个简单的例子才能真正理解它。大多数教程都需要外部库,并使其比需要的更复杂。
以下是我查看过的资源:
Stackoverflow - How to use hsc2hs to bind to constants, functions and data structures?
Haskell Cafe - FFI for a beginner
Writing Haskell interfaces to C code: hsc2hs
编辑:目前我遇到困难(在C中调用setFoo时会出现分段错误)
Haskell Code Snippet
instance Storable Foo where
sizeOf = #{size foo}
alignment = alignment (undefined :: CString)
poke p foo = do
#{poke foo, a} p $ a foo
#{poke foo, b} p $ b foo
#{poke foo, c} p $ c foo
peek p = return Foo
`ap` (#{peek foo, a} p)
`ap` (#{peek foo, b} p)
`ap` (#{peek foo, c} p)
foreign export ccall "setFoo" setFoo :: Ptr Foo -> IO ()
setFoo :: Ptr Foo -> IO ()
setFoo f = do
newA <- newCString "abc"
newB <- newCString "def"
poke f (Foo newA newB 123)
C Code Snippet
foo *f;
f = malloc(sizeof(foo));
foo->a = "bbb"
foo->b = "aaa"
foo->c = 1
// this is incorrect
// setFoo(&f);
// this is correct
setFoo(f);
答案 0 :(得分:8)
这是一个将结构传递给Haskell的C程序的完整示例,然后Haskell会改变该结构的值。它没有外部依赖。如果您有GHC,您应该能够复制代码并运行它。希望这将成为其他人的一个简单明了的例子。
<强> foo.h中强>
typedef struct {
char *a;
char *b;
int c;
} foo;
<强> foo.c的强>
#include "foo.h"
<强> HsFoo.hsc 强>
{-# LANGUAGE ForeignFunctionInterface #-}
{-# LANGUAGE CPP #-}
module HsFoo where
import Foreign
import Foreign.C
import Control.Applicative
import Control.Monad
#include "foo.h"
data Foo = Foo {
a :: CString
, b :: CString
, c :: Int
} deriving Show
instance Storable Foo where
sizeOf _ = #{size foo}
alignment _ = alignment (undefined :: CString)
poke p foo = do
#{poke foo, a} p $ a foo
#{poke foo, b} p $ b foo
#{poke foo, c} p $ c foo
peek p = return Foo
`ap` (#{peek foo, a} p)
`ap` (#{peek foo, b} p)
`ap` (#{peek foo, c} p)
foreign export ccall "free_HaskellPtr" free :: Ptr a -> IO ()
foreign export ccall "setFoo" setFoo :: Ptr Foo -> IO ()
setFoo :: Ptr Foo -> IO ()
setFoo f = do
newA <- newCString "abc"
newB <- newCString "def"
poke f $ Foo newA newB 3
return ()
<强>的main.c 强>
#include <stdio.h>
#include <stdlib.h>
#include "HsFoo_stub.h"
#include "foo.h"
int main(int argc, char *argv[]) {
hs_init(&argc, &argv);
foo *f;
f = malloc(sizeof(foo));
f->a = "Hello";
f->b = "World";
f->c = 55555;
printf("foo has been set in C:\n a: %s\n b: %s\n c: %d\n",f->a,f->b,f->c);
setFoo(f);
printf("foo has been set in Haskell:\n a: %s\n b: %s\n c: %d\n",f->a,f->b,f->c);
free_HaskellPtr(f->a);
free_HaskellPtr(f->b);
free(f);
hs_exit();
}
命令行 - 编译文件并运行
$ hsc2hs HsFoo.hsc
$ ghc -c HsFoo.hs foo.c
$ ghc -no-hs-main foo.c HsFoo.o main.c -o main
$ ./main