I have a C Struct:

   typedef struct
   {
       enum LibRaw_image_formats type;
       ushort      height,
                   width,
                   colors,
                   bits;
       unsigned int  data_size;
       unsigned char data[1];
   }libraw_processed_image_t;

with a D version:

   struct libraw_processed_image_t
   {
       LibRaw_image_formats    type;
       ushort                  height,
                               width,
                               colors,
                               bits;
       uint                    data_size;
       ubyte[1]                data;
   }

libraw_dcraw_make_mem_thumb() returns a pointer to this struct.
I need to create a char[] from the data and data_size members,
ideally without copying, to send to GdkPixbufLoader.write(char[]).

If I do this:
   libraw_processed_image_t *img;
   img = libraw_dcraw_make_mem_thumb();
   char[] buf = cast(char[]) img.data[];
   GdkPixbufLoader.write(buf); // Runtime error

buf.ptr == img.data.ptr and length of both arrays is 1.
If I try:
   buf.length = img.data_size;
buf is reallocated.

Any suggestions to make buf.ptr == img.data.ptr and buf.length = img.data_size?

Thanks
ollie

On 02/04/2014 10:58 AM, ollie wrote:

> I have a C Struct:

[...]

>         uint                    data_size;
>         ubyte[1]                data;

Is that the C extension where the last array in a struct can have more elements than its size? That will be a problem in D.

>     }
>
> libraw_dcraw_make_mem_thumb() returns a pointer to this struct.
> I need to create a char[] from the data and data_size members,
> ideally without copying, to send to GdkPixbufLoader.write(char[]).
>
> If I do this:
>     libraw_processed_image_t *img;
>     img = libraw_dcraw_make_mem_thumb();
>     char[] buf = cast(char[]) img.data[];

This:

  char[] buf = (cast(char*)img.data.ptr)[0  .. img.data_size];

However, as I said above, data won't have room for more than 1 element.

In any case, treating a C array as a D slice is achieved by the following syntax:

    int[] D_slice = C_array[0 .. C_array_number_of_elements];

Ali

On Tue, 04 Feb 2014 11:16:00 -0800, Ali Çehreli wrote:


> Is that the C extension where the last array in a struct can have more elements than its size? That will be a problem in D.

yes it is.

>      int[] D_slice = C_array[0 .. C_array_number_of_elements];

Thank you, that gives me what I was looking for. I thought I had tried something like that. Too many moving parts with threads and context changes to call GDK/GTK functions make things very precarious. I am still getting an access violation, but your help has moved me a step nearer a solution.

Thanks,
ollie

Ali Çehreli:

> Is that the C extension where the last array in a struct can have more elements than its size? That will be a problem in D.

Since V.2.065 D supports well variable-length structs. You have to use ubyte[0] data, and then allocate a large enough memory for the whole variable-length struct. Here I have written an usage example:

http://rosettacode.org/wiki/Sokoban#Faster_Version

Bye,
bearophile