[Haskell-cafe] FFI newbie question

John Meacham john at repetae.net
Fri Mar 14 10:29:25 EDT 2008

On Fri, Mar 14, 2008 at 09:54:11PM +0800, Verma Anurag-VNF673 wrote:
> I am trying to figure out how to pass array of String (char **) from C
> to Haskell?  I have read the FFI examples, but most of them are centered
> on calling C from Haskell. I have read in the mailing list, it is rare
> to call Haskell from C, but my requirement is such that I am going to
> write Haskell library that needs to be called from C. 

here is a simple example. the first argument is the number of strings,
the second is the pointer. The same code will work whether you are
calling C from haskell or vice versa.

getargs :: Int -> (Ptr CString) -> IO [String]
getArgs argc argv = do
        let f n = peekElemOff argv n >>= peekCString
        mapM f [0 .. fromIntegral argc - 1]


John Meacham - ⑆repetae.net⑆john⑈

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