Re: [Valgrind-developers] static array initialisation in C

[Tom H. <th...@cy...>]

In message <Pin...@he...>
        Nicholas Nethercote <nj...@ca...> wrote:

> I want to initialise a static 2-d array in C.  Is this possible?
>
> GCC complains about this:
>
>    const char** a[] = {
>      [0] = { "one", "two", "three", NULL },
>      [1] = { "four", "five", "six", NULL },
>    };
>
> saying:
>
>    b.c:7: warning: braces around scalar initializer
>    b.c:7: warning: (near initialization for `a[0]')

Because a[0] is a pointer - a is an array of pointers to pointers - and
you can't initialise a pointer with an aggregate. C won't just invent
an unnamed array and then take a pointer to it.

If the inner dimension of the array is fixed then this will work:

  const char* a[][4] = {
    [0] = { "one", "two", "three", NULL },
    [1] = { "four", "five", "six", NULL }
  };

Because a is now an array of arrays of pointers so you can initialise
the [0] member with an array.

<fx: goes and reads info gcc>

Actually, it seems that C99 can do it, and possibly GCC did even
before that. The syntax is:

  const char** a[] = {
    [0] = (const char *[]){ "one", "two", "three", NULL },
    [1] = (const char *[]){ "four", "five", "six", NULL }
  };

And "cc -std=c99 -pedantic -Wall" seems to compile that with no
complaints as does gcc in non-pedantic c89 mode. Pedantic C89 mode
refuses it.

> If I break it into two pieces:
>
>    const char* a1[] = { "one", "two", "three", NULL };
>    const char* a2[] = { "four", "five", "six", NULL };
>
>    const char** a[] = {
>      [0] = a1,
>      [1] = a2,
>    };
>
> it works ok, but that doesn't really suit my purpose, because there's
> a macro involved and it would be much more convenient to do the former.

That is the other option.

Tom

-- 
Tom Hughes (th...@cy...)
Software Engineer, Cyberscience Corporation
http://www.cyberscience.com/