Re: Clarification on Gcc's strict aliasing rules

["Segher Boessenkool" <segher at kernel dot crashing dot org>]

>>> 	  int f() {
>>> 	    union a_union t;
>>> 	    int* ip;
>>> 	    t.d = 3.0;
>>> 	    ip = &t.i;
>>> 	    return *ip;
>>> 	  }
>>>
>>> could you tell me what the effective type of 't.i' object ?
>>
>> int, if you can say that object exists at all: it does not have a stored
>> value.  The stored value of t is a double with value 3.0 .  You can
>> take its address and access it via that as "double" (or "char"), or you
>> can access it as the union it is.  You can not access it as "int".
>
> BTW, does your reasoning rely on the C standard ?

Of course it does.  Perhaps I don't understand what you're asking here.

> If so could you let me know which parts exactly ?

C99 6.5/6 defines effective type.  6.5/7 says what accesses are allowed.
If you care about C90 as well, please look it up yourself, I don't have
those docs handy.


Segher