Never seen before C method of initialization of an array of structs found in the Linux kernel source

Question

55 typedef struct pidmap {
56         atomic_t nr_free;
57         void *page;
58 } pidmap_t;
59 
60 static pidmap_t pidmap_array[PIDMAP_ENTRIES] =
61          { [ 0 ... PIDMAP_ENTRIES-1 ] = { ATOMIC_INIT(BITS_PER_PAGE), NULL } };

The code snippet above shows the initialization of an array of a structs that I found in the Linux kernel source. I have never seen this form of initialization before and I couldn't simulate the same thing on my own. What am I missing actually?

Source of the code

Answer 1

It is a GNU/GCC extension called Designated Initializers. You can find more information about it in the GCC documentation.

To initialize a range of elements to the same value, write [first ... last] = value. This is a GNU extension