What does [ N … M ] mean in C aggregate initializers?

问题

From sys.c line 123:

void *sys_call_table[__NR_syscalls] = 
{
    [0 ... __NR_syscalls-1] = sys_ni_syscall,
#include <asm/unistd.h>
};

sys_call_table is a generic pointer to arrays, I can see that. However what is the notation:

[0 ... __NR_syscalls-1]

What is the ...?

---

EDIT:
I learned another C trick here: #include <asm/unistd.h> will be preprocessed and replaced with its content and assigned to [0 ... _NR_syscalls-1].

回答1:

It is initialization using Designated Initializers.

The range based initialization is a gnu gcc extension.

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

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

It is not portable. Compiling with -pedantic with tell you so.

How does it work here?
The preprocessor replaces #include <asm/unistd.h> with its actual contents(it defines miscellaneous symbolic constants and types, and declares miscellaneous functions) in the range based construct, which are then further used for initializing the array of pointers.

来源：https://stackoverflow.com/questions/10071304/what-does-n-m-mean-in-c-aggregate-initializers