[Haskell-beginners] Re: ffi woes

Jose A. Ortega Ruiz jao at gnu.org
Sat Feb 20 04:10:26 EST 2010

Hi Dean,

Dean Herington <heringtonlacey at mindspring.com> writes:


> Though I'm not an FFI expert, I'll take a stab in case it might help you.
> It seems to me that
>>    s <- (#peek struct wireless_info, essid)
>>    peekCString s
> would read a pointer from the essid field, which is clearly not what
> you want.  I think you'd want to use #ptr.  Maybe something like the
> following (untested!):
>     l <- (#peek struct wireless_config, essid_len) wc
>     p <- (#ptr struct wireless_info, essid) wc
>     -- wireless_config.essid is a char[MAX_LEN]
>     peekCStringLen (p, fromIntegral (l :: CInt))

Right, using #ptr works (with the minor modification that it doesn't
return its value inside IO, so one must use let p =..., instead of p <-

Thanks a lot for your help.


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