On Thu, Apr 23, 2009 at 5:39 PM, Joe Buck <joe.b...@synopsys.com> wrote:
>
> On Thu, Apr 23, 2009 at 1:38 PM, Denis Onischenko
>> <denis.onische...@gmail.com> wrote:
>> > The minimal code example is following:
>> >
>> >
>> > extern unsigned int __invalid_size_argument;
>> > #define TYPECHECK(t) ( sizeof(t) == sizeof(t[1]) ? sizeof(t) :
>> > __invalid_size_argument )
>> >
>> > static int arr[] = {
>> > [TYPECHECK(int)] = 0,
>> > };
>> >
>> > int main()
>> > {
>> > return 0;
>> > }
>> >
>> >
>> > command line is: gcc test.c
>> >
>> > GCC 4.5.0 revision 146607 compiles this code with following errors:
>> > test.c:5: error: nonconstant array index in initializer
>> > test.c:5: error: (near initialization for 'arr')
>> >
>> > released GCC 4.4.0 compiles without any errors
>
> On Thu, Apr 23, 2009 at 04:58:17PM -0700, James Dennett wrote:
>> A diagnostic is required in standards-conforming modes, as
>> TYPECHECK(int) is not an "integral constant expression" (because it
>> includes a non-constant in a potentially-evaluated operand).
>
> But there are cases where we avoid issuing such a diagnostic by
> default, without flags such as -pedantic or calling out a specific
> language standard.
>
> The compiler is not supposed to be pedantic by default. A standards
> document saying that a diagnostic is required should not be the end
> of the story, especially when we're talking about important, widely
> used code bases.
Very true. Note that I explicitly refer only to "standards-conforming
modes". Generating warnings for idiomatic use of system headers is
not good for usability, though sometimes hard to avoid.
-- James
