Thanks for your help & time, I checked the C API documentation: http://xmlsoft.org/html/libxml-xmlreader.html#xmlTextReaderValue "The result must be deallocated with xmlFree()"
I pushed the sources here: http://github.com/gwenn/libxml-reader My problem is with the function at line 249 in Text.XML.LibXML.XmlReader To make it work, I have to comment out the line where xmlFree is called. -- xmlChar * xmlTextReaderValue(xmlTextReaderPtr reader) -- Returns:the string or NULL if not available. The result must be deallocated with xmlFree() foreign import ccall unsafe "xmlreader.h xmlTextReaderValue" c_xmlTextReaderValue :: Ptr XmlTextReader -> IO (CString) value :: (MonadIO m) => XmlReader -> m (Maybe B.ByteString) value (XmlReader reader_fp) = liftIO $ withForeignPtr reader_fp $ \reader_ptr -> do cstr <- c_xmlTextReaderValue reader_ptr fromPtr B.packCString cstr c_xmlFree fromPtr :: (Ptr a -> IO b) -> Ptr a -> (Ptr a -> IO ()) -> IO (Maybe b) fromPtr c2h ptr free | ptr == nullPtr = return Nothing | otherwise = do r <- c2h ptr free ptr -- FIXME return (Just r) May be the binding to xmlFree is wrong? foreign import ccall unsafe "xmlreader.h xmlFree" c_xmlFree :: Ptr a -> IO () To test, you will need libxml2-dev: $ runhaskell Setup configure --extra-include-dirs=/usr/include/libxml2/ $ runhaskell Setup build $ ./dist/build/Test/Test C functions are described here: http://xmlsoft.org/html/libxml-xmlreader.html And here: http://xmlsoft.org/html/libxml-globals.html Regards. On Sun, Nov 29, 2009 at 7:02 PM, Duncan Coutts <duncan.cou...@googlemail.com > wrote: > On Sun, 2009-11-29 at 18:00 +0100, El Barto wrote: > > Hello, > > I get a segfault when I do > > str <- peekCString ptr > > free ptr > > return (Just str) > > As Thomas says, you've not really given us enough info here. > > I'll make some guesses and observations anyway :-) > > > But not when I don't free the C pointer. > > Are you sure the C code does not also free the memory? That would lead > to a double-free which can easily manifest as a segfault. > > > I also get the same behaviour with ByteString.packCString... > > That's pretty odd since packCString does not free the C string, it makes > a copy. I suppose it could possibly segfault if your C string was not > actually null terminated (as C strings must be). > > There are also variants that do not copy, such as > unsafePackMallocCString. See the docs for a description. > > > Could you please tell me if the memory is correctly freed by GHC when > > I don't do it myself? > > And how can I specify a custom free function (i.e. xmlFree function in > > libxml2)? > > See the documentation for ForeignPtr. > > > Maybe I should use a data type with two fields : the String/ByteString > > and the ForeignPtr to the CString? > > Is your C String supposed to be freed using the C free() function, or is > it supposed to be freed using xmlFree() or something? > > Duncan > >
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