On 11/12/2010 03:21 PM, Francis Moreau wrote:
> Andrew Haley <aph@xxxxxxxxxx> writes:
>
>> On 11/12/2010 02:55 PM, Francis Moreau wrote:
>>> "Segher Boessenkool" <segher@xxxxxxxxxxxxxxxxxxx> writes:
>>>
>>> [...]
>>
>>>
>>>>>
>>>>> Looking again at the second example:
>>>>>
>>>>> 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 ?
>>
>> It's a gcc extension. 5.25, Cast to a Union Type
>
> How can it be related with the existence of an union member ?
I don't understand your question. Rather than attempt to answer,
I'll ask you to rephrase your question.
It's clear that in an object of type
union a_union {
int i;
double d;
};
the effective type of i is int.
Andrew.
