Re: [Glsdk-devel] The use of anonymous structures

[H. H. <hen...@gm...>]

Indeed. At the moment, I don't have an access to a Windows box, but could
somebody who has, kindly test out the possibility of this.

Does the MSVC produce warnings, when you try to compile something like this:

typedef struct FOO_s {
  union {
    struct {
      int di;
    };
    in do;
  };
} FOO;

int main()
{
  FOO f;
  f.di = 1;
  f.do = 2;
  return 0;
}


On Sun, Aug 24, 2008 at 5:55 AM, Jason McKesson <ko...@gm...> wrote:

>  Henri Häkkinen wrote:
>
>
>
> On Sun, Aug 24, 2008 at 5:14 AM, Stefanos A. <sta...@gm...> wrote:
>
>> Την Sun, 24 Aug 2008 04:05:06 +0300,ο(η) Henri Häkkinen
>> <hen...@gm...> έγραψε:
>>
>> > Does anyone have anything to say on this, please? I am currently working
>> > hard on the GLM and I think we should resolve the issue of how we
>> > actually
>> > define the math types.
>> >
>>
>>  I'd go for #2 (struct/union), just slightly modified.
>>
>> Why use a struct? Because typing vec.x is cleaner than vec[0].
>>
>> Why have a union? So you can pass the struct to OpenGL without a cast.
>> Compare:
>>
>> foo(vec.data);       // approach #2 (struct/union)
>> vs
>> foo((GLfloat*)vec);  // approach #3 (struct)
>> vs
>> foo(&vec.x);         // approach #3 (struct)
>>
>> To that end, it might be better to define structs like this:
>>
>> typedef struct GLMFoo_t
>> {
>>     union GLMFoo_data
>>     {
>>         GLfloat data[2];   // Instead of v[] or m[]
>>         struct GLMFoo_fields
>>         {
>>             GLfloat x, y;
>>         }
>>     }
>> } GLMFoo;
>>
>> This makes clear that the "data" field provides the storage for the vector
>> data - v or m might be somewhat cryptic at first glance.
>>
>
> I agree that we should go with the struct-union combination. However, I
> have discovered a problem:
>
> typedef struct FOO_s {
>   union {
>     int di;
>     struct BAS_s {
>       int do;
>     };
>   };
> } FOO;
>
> FOO f;
> f.di = 1;
> f.do = 2;
>
> This fails on GCC; f.do is not accessible (try it). I am not sure is this a
> bug in GCC or is this standard conforming behaviour. So therefore, we cannot
> go with the non-anonymous inner struct.
>
> I recommend that we go with struct-union, and with anonymous inner struct,
> and just use compiler #pragma (disable : warning) on Windows platform to
> drop the warning it produces.
>
> What do you think?
>
> As you pointed out, D3DX defines a matrix thusly:
>
> typedef struct _D3DMATRIX {
>     union {
>         struct {
>             float        _11, _12, _13, _14;
>             float        _21, _22, _23, _24;
>             float        _31, _32, _33, _34;
>             float        _41, _42, _43, _44;
>
>         };
>         float m[4][4];
>     };
> } D3DMATRIX;
>
>
> Anonymous inner struct and all. It doesn't produce warnings or anything.
> Maybe you just need to have the struct come first in the union.
>
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-- 
Henri 'henux' Häkkinen