The initializer of a structure variable can include a reference to itself, but this case does not work. Order is matter.

structureinitFail.c

/*
	LLVM reports a warning as follows;
	"variable 's' is uninitialized when used within its own initialization [-Wuninitialized]"
	And it shows the answer randomly.
*/
#include <stdio.h>
typedef struct {
	int a, b, c;
} S;
int sum(S s) {
	printf("sub  %d %d %d\n", s.a, s.b, s.c);
	return s.b + s.c;
}
int main() { 
	S s = {sum(s), 1, 2};
	printf("main %d %d %d\n", s.a, s.b, s.c);
	return 0;
}

My Mac shows the result as follows;

$ ./a.out
sub 19 0 123502688
main 123502688 1 2
$ ./a.out
sub 19 0 129785952
main 129785952 1 2
$ ./a.out
sub 19 0 56098912
main 56098912 1 2
$

Original source is here;
https://gist.github.com/yyasuda/bb6c0ad6ffcbf6a526d775c360398a98

It shows the (right) answer "3".

So the order matter. The initializer sets the value from left to right.
As an initializer of a structure variable, it is possible to place a function that refers to the variable itself. However, the function must be aware that only member variables before itself are initialized yet.

The assembled code of above "original" source is here;
https://gist.github.com/yyasuda/c5633cea0e9c9de303f15a3af4c5d324
You can understand what happened inside. How the initializer's order matter.