Question

If you’ve got a struct within a struct, say:

struct {
    double a;
    struct {
        char *b[20];
        char c;
    }d;
}e;

will struct e need to start on a multiple of the size of struct d, or a multiple of the size of the largest member of d (char *b[20])?

Answer 1

It’s compiler- and settings-dependent. In most cases will start at the first member’s granularity, which in your case is sizeof(char*). Note, that it’s not sizeof(char*) * 20, since it’s an array and not a native type. Also note that in your case, the struct e will always start at least at granularity of sizeof(double), and therefore struct d will do too.