berte said:
Hello folks,
I investigating kernel sources I coincided with this part:
struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
[0 ... NR_IRQS-1] = {
.status = IRQ_DISABLED,
.chip = &no_irq_chip,
.handle_irq = handle_bad_irq,
.depth = 1,
.lock = __SPIN_LOCK_UNLOCKED(irq_desc->lock),
#ifdef CONFIG_SMP
.affinity = CPU_MASK_ALL
#endif
}
};
Q1- What is this part "[0 ... NR_IRQS-1]" ?
Q2- Elipsis using with arrays ?
Regards.
This is a gnu extension. In
http://gcc.gnu.org/onlinedocs/gcc-2.95.3/gcc_4.html#SEC88
you can read:
4.20 Labeled Elements in Initializers
Standard C requires the elements of an initializer to appear in a fixed
order, the same as the order of the elements in the array or structure
being initialized.
In GNU C you can give the elements in any order, specifying the array
indices or structure field names they apply to. This extension is not
implemented in GNU C++.
To specify an array index, write `[index]' or `[index] =' before the
element value. For example,
int a[6] = { [4] 29, [2] = 15 };
is equivalent to
int a[6] = { 0, 0, 15, 0, 29, 0 };
The index values must be constant expressions, even if the array being
initialized is automatic.
To initialize a range of elements to the same value, write `[first ...
last] = value'. For example,
int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };
Note that the length of the array is the highest value specified plus one.
In a structure initializer, specify the name of a field to initialize
with `fieldname:' before the element value. For example, given the
following structure,
struct point { int x, y; };
the following initialization
struct point p = { y: yvalue, x: xvalue };
is equivalent to
struct point p = { xvalue, yvalue };
Another syntax which has the same meaning is `.fieldname ='., as shown here:
struct point p = { .y = yvalue, .x = xvalue };
You can also use an element label (with either the colon syntax or the
period-equal syntax) when initializing a union, to specify which element
of the union should be used. For example,
union foo { int i; double d; };
union foo f = { d: 4 };
will convert 4 to a double to store it in the union using the second
element. By contrast, casting 4 to type union foo would store it into
the union as the integer i, since it is an integer. (See section 4.22
Cast to a Union Type.)
You can combine this technique of naming elements with ordinary C
initialization of successive elements. Each initializer element that
does not have a label applies to the next consecutive element of the
array or structure. For example,
int a[6] = { [1] = v1, v2, [4] = v4 };
is equivalent to
int a[6] = { 0, v1, v2, 0, v4, 0 };
Labeling the elements of an array initializer is especially useful when
the indices are characters or belong to an enum type. For example:
int whitespace[256]
= { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };
