On Fri, 28 Nov 2014, Mason wrote:
> On 24/11/2014 17:53, Mason wrote:
>
> > Consider the following code: [big snip]
>
> (Perhaps my previous message was too verbose.)
>
> Why does gcc reject the following code:
>
> union foob { int val; struct { int X; } bits; };
> static const int u = ((union foob) {.bits = { .X=42 }}).val;
>
> $ gcc -std=gnu89 test.c
> test.c:2:30: error: initializer element is not constant
> static const int u = ((union foob) {.bits = { .X=42 }}).val;
For the reason stated in the error message: that initializer is not a
constant expression (it involves access to an anonymous object). There is
a limited allowance in GNU C for when the initializer is a compound
literal of the right type (so that you can define a macro of a structure
or union type that expands to something usable in both assignments and
initializers), but not for any more complicated operations involving them.
--
Joseph S. Myers
joseph@xxxxxxxxxxxxxxxx
