Hi, I have the following code attached, and I do not understand why I can not access this data member. Help is very much appreciated, thanks.

~ Clay

clayasaurus wrote:
> Hi, I have the following code attached, and I do not understand why I can not access this data member. Help is very much appreciated, thanks.
> 
> ~ Clay
> 
> 
> ------------------------------------------------------------------------
> 
> // datafield hacks
> alias int FILE; alias int Uint8; 
> 
> // structure
> struct SDL_RWops
> {
> 
>     int (*seek)(SDL_RWops *context, int offset, int whence);
>     int (*read)(SDL_RWops *context, void *ptr, int size, int maxnum);
>     int (*write)(SDL_RWops *context, void *ptr, int size, int num);
>     int (*close)(SDL_RWops *context);
>     uint type;
> 	
>     union hide
>     {
>         version(Windows)
>         {
>             struct win32io
>             {
>                 int append;
>                 void *h;
>             }
>         }
>         struct stdio
>         {
>             int autoclose;
>             FILE *fp;
>         }
>         struct mem
>         {
>             Uint8 *base;
>             Uint8 *here;
>             Uint8 *stop;
>         }
>         struct unknown
>         {
>             void *data1;
>         }
>     }
> 	hide hidden; 	
> }
> 
> 
> int main()
> {
>     SDL_RWops w; 
> 
>     // need 'this' to access data member data1??
>     w.hidden.unknown.data1 = null; 
> 
>     return 0; }

Because 'SDL_RWops.hidden.unknown' is a struct type decleration, not a field decleration.  In the same way that you had to create a field of type 'hide' in order to access its components ('hidden') you also need a field of type 'unknown' to do so.

-- Chris Nicholson-Sauls

Chris Nicholson-Sauls wrote:
> clayasaurus wrote:
>> Hi, I have the following code attached, and I do not understand why I can not access this data member. Help is very much appreciated, thanks.
>>
>> ~ Clay
>>
>>
>> ------------------------------------------------------------------------
>>
>> // datafield hacks
>> alias int FILE; alias int Uint8;
>> // structure
>> struct SDL_RWops
>> {
>>
>>     int (*seek)(SDL_RWops *context, int offset, int whence);
>>     int (*read)(SDL_RWops *context, void *ptr, int size, int maxnum);
>>     int (*write)(SDL_RWops *context, void *ptr, int size, int num);
>>     int (*close)(SDL_RWops *context);
>>     uint type;
>>         union hide
>>     {
>>         version(Windows)
>>         {
>>             struct win32io
>>             {
>>                 int append;
>>                 void *h;
>>             }
>>         }
>>         struct stdio
>>         {
>>             int autoclose;
>>             FILE *fp;
>>         }
>>         struct mem
>>         {
>>             Uint8 *base;
>>             Uint8 *here;
>>             Uint8 *stop;
>>         }
>>         struct unknown
>>         {
>>             void *data1;
>>         }
>>     }
>>     hide hidden;     }
>>
>>
>> int main()
>> {
>>     SDL_RWops w;
>>     // need 'this' to access data member data1??
>>     w.hidden.unknown.data1 = null;
>>     return 0; }
> 
> Because 'SDL_RWops.hidden.unknown' is a struct type decleration, not a field decleration.  In the same way that you had to create a field of type 'hide' in order to access its components ('hidden') you also need a field of type 'unknown' to do so.
> 
> -- Chris Nicholson-Sauls

Thanks.
~ Clay

On Tue, 26 Sep 2006 22:22:05 -0500, clayasaurus wrote:

> Hi, I have the following code attached, and I do not understand why I can not access this data member. Help is very much appreciated, thanks.

As explained already, a named union/struct must also have a data declaration before you can refer to its members. However, have you considered anonymous union/struct ? When you use these, you can refer to the members without having to qualify their names.

import std.stdio;
// datafield hacks
alias int FILE;
alias int Uint8;

// structure
struct SDL_RWops
{

    int (*seek)(SDL_RWops *context, int offset, int whence);
    int (*read)(SDL_RWops *context, void *ptr, int size, int maxnum);
    int (*write)(SDL_RWops *context, void *ptr, int size, int num);
    int (*close)(SDL_RWops *context);
    uint type;

    union
    {
        version(Windows)
        {
            struct
            {
                int append;
                void *h;
            }
        }
        struct
        {
            int autoclose;
            FILE *fp;
        }
        struct
        {
            Uint8 *base;
            Uint8 *here;
            Uint8 *stop;
        }
        struct
        {
            void *data1;
        }
    }
}


int main()
{
    SDL_RWops w;

    // need 'this' to access data member data1??
    std.stdio.writefln("autoclose A:" , w.autoclose);

    w.data1 = &w; // sample data
    std.stdio.writefln("autoclose B:" , w.autoclose);

    version(Windows)
    {
     w.append = 42; // sample data
     std.stdio.writefln("autoclose B:" , w.autoclose);
    }
    return 0;
}



-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
"Down with mediocrity!"
27/09/2006 3:22:49 PM

Derek Parnell wrote:
> On Tue, 26 Sep 2006 22:22:05 -0500, clayasaurus wrote:
> 
>> Hi, I have the following code attached, and I do not understand why I can not access this data member. Help is very much appreciated, thanks.
> 
> As explained already, a named union/struct must also have a data
> declaration before you can refer to its members. However, have you
> considered anonymous union/struct ? When you use these, you can refer to
> the members without having to qualify their names.
> 
> import std.stdio;
> // datafield hacks
> alias int FILE;
> alias int Uint8;
> 
> // structure
> struct SDL_RWops
> {
> 
>     int (*seek)(SDL_RWops *context, int offset, int whence);
>     int (*read)(SDL_RWops *context, void *ptr, int size, int maxnum);
>     int (*write)(SDL_RWops *context, void *ptr, int size, int num);
>     int (*close)(SDL_RWops *context);
>     uint type;
> 
>     union
>     {
>         version(Windows)
>         {
>             struct
>             {
>                 int append;
>                 void *h;
>             }
>         }
>         struct
>         {
>             int autoclose;
>             FILE *fp;
>         }
>         struct
>         {
>             Uint8 *base;
>             Uint8 *here;
>             Uint8 *stop;
>         }
>         struct
>         {
>             void *data1;
>         }
>     }
> }
> 
> 
> int main()
> {
>     SDL_RWops w;
> 
>     // need 'this' to access data member data1??
>     std.stdio.writefln("autoclose A:" , w.autoclose);
> 
>     w.data1 = &w; // sample data
>     std.stdio.writefln("autoclose B:" , w.autoclose);
> 
>     version(Windows)
>     {
>      w.append = 42; // sample data
>      std.stdio.writefln("autoclose B:" , w.autoclose);
>     }
>     return 0;
> }
> 

That would be nicer, but it is not my call. The SDL_RWops structure is from the SDL library (www.libsdl.org) and the goal is to stay as close to the original structure as possible.

clayasaurus wrote:

>>
> 
> That would be nicer, but it is not my call. The SDL_RWops structure is from the SDL library (www.libsdl.org) and the goal is to stay as close to the original structure as possible.
> 
> 

In C, named inner structs and unions are treated as fields.

This...

##############
typedef struct
{
   struct foo
   {
      int x;
   }
} MyStruct;

MyStruct ms;
ms.foo.x = 0;
##############

...is identical to this...

##############
typedef struct
{
   int x;
} Foo;

typedef struct
{
   Foo foo;
} MyStruct;

MyStruct ms;
ms.foo.x = 0;
##############

Assuming a 32 bit C compiler, both sizeof(MyStruct) in both examples above should output '4'.

In D, inner structs and unions are treated as type declarations but not members. Here is the same example in D:

##############
struct MyStruct
{
   struct foo
   {
      int x;
   }
}
MyStruct ms;
ms.foo.x = 0; // Error
#############

MyStruct.sizeof will output 1 in this example. Not only is foo not accessible as a member field, MyStruct is incompatible with the C side of the house. The following version fixes both issues:

##############
struct MyStruct
{
   struct Foo
   {
      int x;
   }
   Foo foo;
}
MyStruct ms;
ms.foo.x = 0;
##############

Now the output of MyStruct.sizeof should be the same as the C version.

DerelictSDL was a tedious port, so I'm surprised more silliness like this hasn't turned up yet. I'm glad you caught it.

Mike Parker wrote:
> clayasaurus wrote:
> 
>>>
>>
>> That would be nicer, but it is not my call. The SDL_RWops structure is from the SDL library (www.libsdl.org) and the goal is to stay as close to the original structure as possible.
>>
>>
> 
> In C, named inner structs and unions are treated as fields.
> 

And now that I've posted that I see that Derek was talking about anonymous inner structs. Oh well, what I said is still true :)