Nil and NULL
- From: QuentinC <webmaster@xxxxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Sun, 05 Aug 2012 18:12:13 +0200
Hello,
Would it be possible to do so that cdata pointers pointing to NULL gets
translated in lua either to actual nil, or at least be interpreted as
being false in a if/while statement ?
The usecase is very simple: an FFI function creates an object and
returns a pointer to the created object, but sometimes the creation can
fail for whatever reason.
Basic example with malloc :
ffi.cdef[[ void* malloc (int size); ]]
local pointer = ffi.C.malloc(123)
if not pointer then print('malloc failed') end -- this looks reasonably
correct but is actually not
The if is never executed. IF the malloc fails, it returns a cdata
encapsuling a NULL pointer, and this cdata is interpreted as true anyway.
I think that a NULL cdata pointer should be converted to false when
using in a if statement as I did above (of course not only void* but all
pointers)
Notice also that there isn't any simple way to check the nullity:
currently the way I found is to convert first to intptr_t, then to
number with the tonumber function, and finally compare it to 0 :
function isnull (pointer)
local intval = ffi.cast('intptr_t', pointer)
local num = tonumber(intval)
return num==0
end
Quite long just for a so trivial operation, isn't it ?
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