Am 24.09.22 um 09:38 schrieb Arrigo Marchiori:
Hello,
On Fri, Sep 23, 2022 at 07:08:26AM +0200, Peter Kovacs wrote:
Hi all,
We cast int to (void*) -> (example in main/sw/source/ui/fldui/changedb.cxx
line 234)
In general this sounds like not a sane idea to me, see discussions [1] [2]
[3]. The solution that the c++ community found is the use of intptr_t, which
is defined in C99.
In general I would like to get rid of these casts. However as a quick fix it
would make sense to use intptr_t as a first measure.
IMHO casting int to void* is not as bad as it seems.
I just note, I dont like this pattern in general. It makes maintenance
in general more difficult.
Your cited sources explains that there would be problems with
_round-tripping_ i.e. using an int type to pass a pointer.
The reason is that on some architectures pointers (void*) are
represented with more bits than integers. Notable example: Linux on
x86_64.
As long as we are using pointers as ``general purpose integers'' we
should have no problems because they are ``big enough'' to contain any
integer value _and_ any pointer.
From my understanding the warning we receive is triggered when:
|sizeof(void*)!=sizeof(int)|
|Which means the issue can aizue on machines / compilers.|
|I dont think ignoriing this issue is a good measurement. Especially,
since the CPU Architectures change now.
|
Is there any reason that would block the move to C99? I guess C99 should be
supported by all the compilers we require . (c11 is currently not available
on all Plattforms we support.)
Unfortunately, Visual Studio 2008 does not support C99. Specifically
for this case, it is missing the definition of the intptr_t type.
Wikipedia [4] gives more information about C99 support in Visual Studio.
I hope this helps.
Ahhh thanks. So C99 is not a way at this point. I guess casting to long
instead is also not great option.
I think of something. It has not the highest priority. Buit as expected
a solution does not seem to be simple.
[1]https://stackoverflow.com/questions/26805461/why-do-i-get-cast-from-pointer-to-integer-of-different-size-error
[2]https://stackoverflow.com/questions/25381610/cast-int-to-pointer-why-cast-to-long-first-as-in-p-void-42
[3]https://stackoverflow.com/questions/6326338/why-when-to-use-intptr-t-for-type-casting-in-c
[4]https://en.wikipedia.org/wiki/Microsoft_Visual_C%2B%2B#C
