Re: [PATCH][2.6.6-rc3] gcc-3.4.0 fixes

["Ihar 'Philips' Filipau" <filia@softhome.net>]

Denis Vlasenko wrote:
> On Thursday 29 April 2004 12:30, Ihar 'Philips' Filipau wrote:
> 
>>Mikael Pettersson wrote:
>>
>>>This patch fixes three warnings from gcc-3.4.0 in 2.6.6-rc3:
>>>- drivers/char/ftape/: use of cast-as-lvalue
>>> 		if (get_unaligned((__u32*)ptr)) {
>>>-			++(__u32*)ptr;
>>>+			ptr += sizeof(__u32);
>>> 		} else {
>>
>>   Can anyone explain what is the problem with this?
>>   To me it seems pretty ligitimate code - why it was outlawed in gcc 3.4?
> 
> 
> cast is not a lvalue. ++(__u32*)ptr is nonsense, just like ++4.
> 

   Yes. I see. C goes in direction of C++.
   For me cast in C is always "forget original type and assume this type."
   From this standpoint it makes a lot of sense. Is just like
((stuct { char a,b,c,d;})4).a - never tryed it in gcc (3.3 does not 
accept it), but IIRC was possible on old PC C compilers - Turbo C 2/3 - 
not sure name/version, but I used it. (Yes! recalled - M$VC/winbase.h 
use this kind of macros for manipulating bytes/words/dwords/etc)
   And in old C classes it was always said that in C you can convert 
anything to everything, it just size of types must be the same.

   Why not after all?

> 
> ptr = (void*) ((char*)ptr + sizeof(__u32));

   No Nice, But Accepted.

   I have just checked my code base - I do not use this feature in any 
way ;-)

-- 
Ihar 'Philips' Filipau  / with best regards from Saarbruecken.
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