From: Vegard Nossum <[email protected]>
Date: Fri, 20 May 2016 14:04:54 +0200

> Just out of curiosity, was this observed in practice? I could be
> wrong, but I was under the impression that using designated
> initializers would zero the rest of the struct, including padding.

I compiled testcases and found that the compiler does not zero out
padding when using designated initializers.

You can do the same.

For example, on sparc 32-bit, this code:

struct foo {
        int a;
        short b;
        int c;
};

extern void foo(struct foo *);

void bar(void)
{
        struct foo f = { .a = 1, .b = 2, .c = 3 };

        foo(&f);
}

gives:

        mov     1, %g1
        st      %g1, [%fp-12]
        mov     2, %g1
        sth     %g1, [%fp-8]
        mov     3, %g1
        st      %g1, [%fp-4]

It does not initialize the padding between 'b' and 'c'.

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