Kai Henningsen wrote:
> [email protected] (Ian Lance Taylor) wrote on 20.01.06 in
> <[EMAIL PROTECTED]>:
>
>> When dealing with unions, you can take pointers to different fields in
>> the unions. If the fields have different types, these pointers can
>> have non-conflicting alias sets. Therefore within a single union the
>> same memory can be read or written by different pointers. This is
>> considered to be invalid--a valid program is required to always access
>> the memory within the union in the same type, except if you access the
>> memory via the union type itself (this permission being a gcc
>> extension).
>
> void test(void)
> {
> union { int i; double d; } u;
> int *ip;
> double *dp;
> int ii;
> double dd;
>
> ip = &u.i;
> *ip = 15;
> ii = *ip;
> dp = &u.d;
> *dp = 1.5;
> dd = *dp;
> printf("ii=%d dd=%f\n", ii, dd);
> }
>
> So you're saying this function is not valid?
>
> MfG Kai
I think he's saying that _this_ one might generate invalid code:
void test(void)
{
union { int i; double d; } u;
int *ip;
double *dp;
int ii;
double dd;
dp = &u.d;
ip = &u.i;
*ip = 15;
ii = *ip;
*dp = 1.5;
dd = *dp;
printf("ii=%d dd=%f\n", ii, dd);
}
cheers,
DaveK
--
Can't think of a witty .sigline today....
