How handle pointer to structs as array ? #341

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1. dcharkes commented on Jan 22, 2022

   

   dcharkes

   on Jan 22, 2022

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   Do you want an array of struct values or an array of struct pointers?

   If you want an array of struct values, you should not use Pointer<Pointer<ncmenu_item>> just Pointer<ncmenu_item>. (Pointers already provide array access.)

   class ncmenu_item extends ffi.Struct {
     external ffi.Pointer<ffi.Int8> description;
     // ignored next  field.
   }
   
   class ncmenu_section extends ffi.Struct {
     external ffi.Pointer<ffi.Int8> name;
     @ffi.Int32()
     external int itemcount;
     external ffi.Pointer<ncmenu_item> items;
   }
   
   void main() {
     using((Arena allocator) {
       final pItems = allocator<ncmenu_item>(2);
       pItems[0]..description = "Foo".toNativeUtf8(allocator: allocator).cast();
       pItems[1]..description = "Bar".toNativeUtf8(allocator: allocator).cast();
   
       final sec = allocator<ncmenu_section>(1);
       sec.ref
         ..name = "Section Menu".toNativeUtf8(allocator: allocator).cast()
         ..items = pItems.cast<ncmenu_item>()
         ..itemcount = 2;
   
       // Use allocated things.
   
       // All allocations in Arena are freed at the end of this scope.
     });
   }

   P.S. you can use the Arena allocator with using(...) to automatically free memory at the end of the scope.

   If you want an array of struct pointers, your C type should be:

   struct ncmenu_section {
     const char* name; 
     int itemcount;
     struct ncmenu_item** items; // note the `**`.
   }

   (But based on https://notcurses.com/html/structncmenu__section.html I'm guessing you're not looking for that.)
2. kascote commented on Jan 22, 2022

   

   kascote

   on Jan 22, 2022

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   worked nice!! thanks!
3. mannprerak2

   closed this as completedon May 28, 2022
4. liamappelbe

   transferred this issue fromdart-archive/ffigenon Nov 15, 2023
5. liamappelbe

   added

   package:ffigen

   on Nov 15, 2023