Hello,
On Tue, September 15, 2009 00:09, Jan-Jaap van der Geer wrote:
> I wonder how to "vapify" a struct that has a variable part at the
> end, such as the wimp_menu below (somewhat simplyfied):
>
> struct wimp_menu_entry
> { wimp_menu_flags menu_flags;
> wimp_menu *sub_menu;
> };
>
> #define wimp_MENU_MEMBERS \
> int width; \
> int height;
>
> struct wimp_menu
> { wimp_MENU_MEMBERS
> wimp_menu_entry entries [UNKNOWN];
> };
>
> UNKNOWN is defined to be 1, but the intended structure can be any
> length, dependent on what is apropriate. It is actually recommended
> to use a macro for defining the structure:
>
> #define wimp_MENU(N) \
> struct \
> { wimp_MENU_MEMBERS \
> wimp_menu_entry entries [N]; \
> }
>
> I wonder how to do this. Somehow Vala needs to know how to allocate
> and free the memory for these structures, so I suppose it somehow
> needs to be told - but I do not know how.
>
> Any ideas?
YUCK! Many objects in GLib are actually allocated with different size
than declared, but it is always hidden in allocator functions.
I see several options:
1) Get the C API redefined to use:
struct wimp_menu {
int width;
int height;
wimp_menu_entry *entries;
};
This could easily be bound in vala as a struct and all expected
operations would work on it, too (well, would also need a length
there).
In C, this has the disadvantage, that the entries array must be
declared as a separate variable.
2) Get a dynamic allocator into the API. It should look like:
wimp_menu_entry_new(int n);
or better
wimp_menu_entry_new(int n, wimp_menu_entry[] entries);
(where the entries will be copied to the allocated structure)
Than you can bind the wimp_menu_entry as a [Compact] class and bind
this method as it's constructor. If you get the later, you can bind
it as
[Compact]
public class Menu {
...
public Menu([CCode(array_length_pos = 0.9)] MenuEntry[] entries);
...
A delete function does not need to be defined, because you can easily
specify
[CCode(free_function = "free")]
(or g_free, depending on whether it will be allocated with malloc or
g_malloc)
on the class definition.
3) Define the allocator function in a helper header in your project.
It could be a macro like:
#define wimp_menu_entry_new(int n) \
g_malloc0(sizeof(wimp_menu) + \
(n - 1) * sizeof(wimp_menu_entry))
The other definition would be more useful, because you wouldn't
have to set the entries item-by-item, but also a bit more complicated.
> Related: Is there documentation about this? If so where can I find
> that?
Very scarce. Look through the wiki, but mostly you will have to
look how similar things are done in the existing .vapi files.
--
- Jan Hudec <[email protected]>
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