c - How to do this initialization? -

i have structure, need initialize @ compile time. here current (pseudo)code:

struct {     int a;     int b; };  struct b {     struct а[16][3]; };  #define default {{ \                    .a = 1, \                    .b = 2, \                  }, \                   { \                    .a = 3, \                    .b = 8, \                  }, \                  { \                    .a = 11, \                    .b = 29, \                 }}  #define default2 default, default #define default4 default2, default2 #define default8 default4, default4 #define default16 default8, default8  struct b b = {{default16}}; 

i don't understand code:

• why need double braces on last line?

• moreover, why need double braces in definition of default. understand

               {                .a = 3,                .b = 8,              } 

is ordinary structure initialization. second pair of braces seems if initializing b array of 16 objects of type struct [3]. why not list values of b if 1-dimensional array (the same way 1 can access b[20])?

• thirdly, need add new field struct b , have no idea how modify initialization. new struct b shall be:

               struct b              {                 int c[16];                 struct a[16][3];              } 

compiler arm-none-eabi-gcc 4.7.2 no flags enforce c standard.

if understand correctly,

one brace needed things within struct a, e.g.

struct a = { .a = 1, .b = 2 }; 

two braces needed 2 dimensional array, e.g.

int array[2][2] = {   { 1, 1 },   { 1, 1 } }; 

the final brace needed things within struct b.

finally, add int c[16] struct b, can replace last line of snippet following:

struct b b = {{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},{default16}}; 

or use proper macro substitution readability.