FFI: Creating a Storable for a C-struct composed of char arrays
Hi all, I'm trying to make RFC calls to SAP using the nwsaprfc library. Some structs defined in the library contains arrays (byte or word arrays). For example: typedef struct _RFC_ATTRIBUTES { SAP_UC dest[64+1]; /* RFC destination */ SAP_UC host[100+1]; /* Own host name */ SAP_UC partnerHost[100+1]; /* Partner host name */ SAP_UC sysNumber[2+1]; /* R/3 system number */ SAP_UC sysId[8+1]; /* R/3 system name */ SAP_UC client[3+1]; /* Client */ SAP_UC user[12+1]; /* User */ SAP_UC language[2+1]; /* Language */ ... continued }}RFC_ATTRIBUTES, *P_RFC_ATTRIBUTES; I would like to create a Haskell Storable counterpart of this structure. Using http://therning.org/magnus/archives/tag/hsc2hs as an starting point, I could create Storable for structures containing fields with basic types. Before working on the real data structures I wrote a more simple example to play with: -- File: ArrayStruct.h -- typedef struct _ArrayStruct { char a[10+1]; char b[20+1]; char c[30+1]; } ArrayStruct, *P_ArrayStruct; -- File: ArrayStruct.c -- #include "ArrayStruct.h" void print_array_struct(ArrayStruct *f) { printf("%s\n", __FUNCTION__); printf("f->a: %s\n", f->a); printf("f->b: %s\n", f->b); printf("f->c: %s\n", f->c); } -- File: HArrayStruct.hsc {-# OPTIONS -ffi #-} module Main where import Foreign import Foreign.C.Types #include "ArrayStruct.h" data HArrayStruct = HArrayStruct { a :: String, b :: String, c :: String } type HarrayStructPtr = Ptr HArrayStruct foreign import ccall "static ArrayStruct.h print_array_struct" f_print_array_struct :: ArrayStructPtr -> IO () instance Storable HArrayStruct where sizeOf _ = (#size ArrayStruct) alignment _ = alignment (undefined :: CInt) peek _ = error "peek is not implemented" poke ptr (HArrayStruct a' b' c') = do (#poke ArrayStruct, a) ptr a' (#poke ArrayStruct, b) ptr b' (#poke ArrayStruct, c) ptr c' printArrayStruct as = with as f_print_array_struct main = printArrayStruct $ HArrayStruct { a="some", b="test", c="data" } -- End of files Of course it won't work as HArrayStruct in file HArrayStruct.hs uses Strings and String is not an instance of Storable. Ideally I would need some sort of Storable array of char. Is Data.Storable.Array the type I'm looking for? Could someone point me to some code using the same kind of structures? Thanks, Olivier.
On 2008 May 9, at 9:42, Olivier Boudry wrote:
Of course it won't work as HArrayStruct in file HArrayStruct.hs uses Strings and String is not an instance of Storable.
Ideally I would need some sort of Storable array of char. Is Data.Storable.Array the type I'm looking for? Could someone point me to some code using the same kind of structures?
You want CString (Foreign.C.String). -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH
Hi Brandon, Thanks for your help, CString will work great for Char arrays, but what about the 16bit-Word arrays? I was not clear in my previous post but the structures used in the nwrfcsdk library can use 8bit or 16 bit "chars" depending on a #define (#define SAPwithUNICODE). Reading another post on FFI in this mailing list I found a link to the following page http://haskell.org/haskellwiki/Modern_array_libraries with a section on StorableArrayS. I'm now trying to use this example code to get StorableArray to work. I will try to use Data.Encoding to convert Haskell StringS to ASCII or UTF16 ByteStringS. Then unpack those ByteStringS to Word8 list and populate StorableArrayS with the bytes. I hope it'll do the job for both Word8 and Word16 arrays. Olivier. On Fri, May 9, 2008 at 9:52 AM, Brandon S. Allbery KF8NH < allbery@ece.cmu.edu> wrote:
On 2008 May 9, at 9:42, Olivier Boudry wrote:
Of course it won't work as HArrayStruct in file HArrayStruct.hs uses Strings and String is not an instance of Storable.
Ideally I would need some sort of Storable array of char. Is Data.Storable.Array the type I'm looking for? Could someone point me to some code using the same kind of structures?
You want CString (Foreign.C.String).
-- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH
Hello Olivier, Friday, May 9, 2008, 6:28:38 PM, you wrote:
Thanks for your help, CString will work great for Char arrays, but what about the 16bit-Word arrays?
TString. they are used a lot for interfacing with Win32 API -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com
participants (3)
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Brandon S. Allbery KF8NH -
Bulat Ziganshin -
Olivier Boudry