[PD-dev] how to cast printed pointers? (commit c019784b83 throwing warnings)

[Christof Ressi]

> I presume there's a good reason to change the code (what if "long" is the wrong
> size?) but I'd like to figure out a way to do it that doesn't throw warnings.
Ok, now I understand the reason for those few (unsigned long) casts. 
It's because the printf() family functions will check the format 
specifier, but the sys_vgui() function, which is used most of the time, 
does not.

However, casting a pointer to (unsigned long) will give a warning on 
64-bit Windows, so one of us will always get warnings either way :-)

See here for a discussion how to actually fix the problem: 
https://github.com/pure-data/pure-data/issues/1474

NOTE: although %p would be the obvious choice, we can't use it, because 
the result is platform/compiler dependent. This is not a problem most of 
the time but it can break in the case of a remote GUI! We really want 
the pointer ID to look the same on all platforms!

Christof

On 03.12.2021 09:51, Albert Rafetseder wrote:
>> After merging commit c019784b83 (get rid of a 3 more bogus (unsigned long) casts)
> (Link to commit for reference: [0] )
>
>> I'm now getting compiler warnings like this:
>>
>> g_editor.c:1884:73: warning: format ‘%lx’ expects argument of type ‘long unsigned int’, but argument 4 has type ‘struct _glist *’ [-Wformat=]
>>   1884 |             snprintf(cbuf, MAXPDSTRING - 2, "pdtk_canvas_setparents .x%lx", c);
>>        |                                                                       ~~^   ~
>>        |                                                                         |   |
>>        |                                                                         |   struct _glist *
>>        |                                                                         long unsigned int
>>
>>
>> ..
>> I presume there's a good reason to change the code (what if "long" is the wrong
>> size?) but I'd like to figure out a way to do it that doesn't throw warnings.
> My C has oxidized substantially over time, but I think the p conversion
> specifier might be the correct thing to use -- if you can live with the
> additional leading "0x" that is caused by its implied "alternate form"
> flag, `#`.
>
>  From `man snprintf` on Linux / OS X:
>
> """
> p       The void * pointer argument is printed in hexadecimal (as if by
>               `%#x' or `%#lx').
> """
>
> Trying with the current master [1] which includes the commit above, the
> change from `%lx` to `%p` in lines 1884 and 1891 in `g_editor.c` fixes
> the warning. (Other warnings/errors remain, and I wouldn't have a clue
> what to test to check the outcome anyway.)
>
> Best,
>    Albert.
>
> [0]
> https://github.com/pure-data/pure-data/commit/c019784b83f6638a1c4090ce27e6a0036b6bacaa
> [1]
> https://github.com/pure-data/pure-data/commit/364d859aa29c1d42be1d42ad81c74bc2fbc76cca
>
>
>
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