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

[Christof Ressi]

IOhannes has the answer: the resulting string might not be valid Tcl 
variable name.

For further discussion see: 
https://github.com/pure-data/pure-data/issues/1474#issuecomment-985386181

On 03.12.2021 10:39, Christof Ressi wrote:
>> 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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>
>
>
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