On Sun, Feb 12, 2012 at 8:18 AM, Yves Parès
Hello,
According to the documentation (http://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/Foreign-St...), StablePtrs aims at being opaque on C-side. But they provide functions to be casted to/from regular void*'s. Does that mean if for instance you have a StablePtr CInt you can cast it to Ptr () and alter it on C-side?
void alter(void* data) { int* x = (int*)data; *x = 42; }
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-- using 'unsafe' doesn't change anything. foreign import ccall safe "alter" alter :: Ptr () -> IO ()
main = do sptr <- newStablePtr (0 :: CInt) deRefStablePtr sptr >>= print alter (castStablePtrToPtr sptr) -- SEGFAULTS! deRefStablePtr sptr >>= print freeStablePtr sptr
But I tried it, and it doesn't work: I got a segfault when 'alter' is called.
I think that 'castStablePtrToPtr' exists because many C APIs use 'void*' to mean 'opaque lump of data', and these exist to conform to that sort of API. Antoine