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

[Christof Ressi]

> 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! 
Hmmm... on a second thought I forgot why this would be a problem... the 
IDs are only generated in the core and GUI app shouldn't care.

So Albert is right, why don't we use %p everywhere?

Christof

On 03.12.2021 10:34, Christof Ressi wrote:
>> 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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