Question

I came across what I thought was a unique syntax that I’ve never seen before (I mostly come from a C++ background). I’m not sure what the code is below. My guess is that it’s some sort of unique way of defining a struct, but if someone could clearly explain what they’re doing here, that would be a great help!

static Foo f =
{

    .a = {DEFAULT_FOO},
    .b = DEFAULT_BAR,
    .c[0] = { 0 }

#ifdef BAR
    ,
    .c[1] = { 0 },
    .c[2] = { 0 }
#endif
};

Answer 1

This is C99 initialization syntax.

Note that a final comma is ok in C99, and the snippet could have been written

static Foo f =
{
    .a = {DEFAULT_FOO},
    .b = DEFAULT_BAR,
    .c[0] = { 0 },
#ifdef BAR
    .c[1] = { 0 },
    .c[2] = { 0 },
#endif
};

Note comma after .c[0] and .c[2].