ctypes from_param() truncating 64 bit pointers to 32 bit

Joakim Hove joakim.hove at gmail.com
Fri Feb 18 03:46:44 EST 2011

Thanks for answering;

> I rarely use ctypes

You should :-) Apart from my current struggle I think ctypes is really

> and I actually don't know how this specific case works.
> However, you are not providing a function signature for the "print_addr" C
> function in the BugTest case, so my guess is that it assumes the standard
> signature for C functions, which is "int func(int)". That would explain the
> 32bit truncation.

Well; I think you are wrong. First of all because what I showed in the
Stackoverflow post was just a contrived example - the real code where
the problem initially arose does indeed have the proper function
signature. Secondly: <Uncertain>The use function signatures will be
relevant for C-C linkage, but ctypes library only relates to the fully
linked shared librarry lib.so where these signatures have been long
lost anyway; that is why we have to specify the argtypes and restype
attributes of the ctypes function objects?</Uncertain>.


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