c - Strange array initialize expression? -

what meaning of following code? code regression test suite of gcc.

static char * name[] = {    [0x80000000]  = "bar" }; 

in c99 can specify array indices assigned value, example:

static char * name[] = {    [3]  = "bar"   }; 

is same as:

static char * name[] = { null, null, null, "bar"}; 

the size of array four. check example code working @ ideaone. in code array size 0x80000001 (its hexadecimal number).
note: uninitialized elements initialized 0.

5.20 designated initializers:

in iso c99 can give elements in order, specifying array indices or structure field names apply to, , gnu c allows extension in c89 mode well. extension not implemented in gnu c++. specify array index, write [index] = before element value. example,

 int a[6] = { [4] = 29, [2] = 15 }; 

is equivalent to

 int a[6] = { 0, 0, 15, 0, 29, 0 }; 

one more interesting declaration possible in gnu extension:

an alternative syntax has been obsolete since gcc 2.5 gcc still accepts write [index] before element value, no =.

to initialize range of elements same value, write [first ... last] = value. example,

 int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };  

note: length of array highest value specified plus one.

additionally, can combine technique of naming elements ordinary c initialization of successive elements. each initializer element not have designator applies next consecutive element of array or structure. example:

 int a[6] = { [1] = v1, v2, [4] = v4 }; 

is equivalent to

 int a[6] = { 0, v1, v2, 0, v4, 0 }; 

labeling elements of array initializer useful when indices characters or belong enum type. example:

 int whitespace[256]  = { [' '] = 1,  ['\t'] = 1, ['\h'] = 1,                           ['\f'] = 1, ['\n'] = 1, ['\r'] = 1                          };