Nested struct variable initialization - c

Question

How can I initialize this nested struct in C?
typedef struct _s0 {
int size;
double * elems;
}StructInner ;
typedef struct _s1 {
StructInner a, b, c, d, e;
long f;
char[16] s;
}StructOuter; StructOuter myvar = {/* what ? */ };

Answer 1

To initialize everything to 0 (of the right kind)
StructOuter myvar = {0};
To initialize the members to a specific value
StructOuter myvar = {{0, NULL}, {0, NULL}, {0, NULL},
{0, NULL}, {0, NULL}, 42.0, "foo"};
/* that's {a, b, c, d, e, f, s} */
/* where each of a, b, c, d, e is {size, elems} */
Edit
If you have a C99 compiler, you can also use "designated initializers", as in:
StructOuter myvar = {.c = {1000, NULL}, .f = 42.0, .s = "foo"};
/* c, f, and s initialized to specific values */
/* a, b, d, and e will be initialized to 0 (of the right kind) */

Answer 2

To highlight struct labels in particular:
StructInner a = {
.size: 1,
.elems: { 1.0, 2.0 }, /* optional comma */
};
StructOuter b = {
.a = a, /* struct labels start with a dot */
.b = a,
a, /* they are optional and you can mix-and-match */
a,
.e = { /* nested struct initialization */
.size: 1,
.elems: a.elems
},
.f = 1.0,
.s = "Hello", /* optional comma */
};

Answer 3

double a[] = { 1.0, 2.0 };
double b[] = { 1.0, 2.0, 3.0 };
StructOuter myvar = { { 2, a }, { 3, b }, { 2, a }, { 3, b }, { 2, a }, 1, "a" };
It seems a and b cannot be initialized in-place in plain C

Answer 4

Following also works with GCC, C99. GCC doesnt complain about it. I am not sure if this is standard.
double arr[] = { 1.0, 2.0 }; // should be static or global
StructOuter myvar =
{
.f = 42,
.s = "foo",
.a.size = 2,
.a.elems = &arr,
.b.size = 0, // you can explicitly show that it is zero
// missing members will actually be initialized to zero
};