Initializing an array member of a struct by name

Question

I have a struct that looks something like this:

typedef struct
{
    uint32_t a;
    uint32_t b;
    uint32_t c[5];
    uint32_t d;
} MY_STRUCT_T;

I want to initialize c, by name, to a non-zero value. I want everything else to be 0.

If c were not an array, I could do:

static MY_STRUCT_T my_struct = {.b = 1};

And I know I can do this:

static MY_STRUCT_T my_struct = {.c[0]=5,
    .c[1]=5,
    .c[2]=5,
    .c[3]=5,
    .c[4]=5};

but I was wondering if there was a more elegant syntax of which I am unaware: Something like:

static MY_STRUCT_T my_struct = {.c[] = {5,5,5,5,5}};

I have read the following, but they don't answer this question:
Initializing a struct to 0
Initialize/reset struct to zero/null
A better way to initialize a static array member of a class in C++ ( const would be preferred though )
How to initialize all members of an array to the same value?

Little difference between this and [How to initialize all members of an array to the same value](http://stackoverflow.com/q/201101/2410359) aside from the `.c=` part. — chux - Reinstate Monica, Sep 12 '16 at 23:05

score 3 · Answer 1 · answered Sep 12 '16 at 20:45

3

So I wrote this question and then experimented for a while and found that the following would work:

static MY_STRUCT_T my_struct = {.c={5,5,5,5,5}};

answered Sep 12 '16 at 20:45

Frederick

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I think `static MY_STRUCT_T my_struct = {.c={5}};` works too. – Jean-François Fabre Sep 12 '16 at 20:46
@Jean-FrançoisFabre: This will initialize all but first element of `c` array member with zeros (just like in ordinary array initialization). – Grzegorz Szpetkowski Sep 12 '16 at 21:31
@GrzegorzSzpetkowski: I think I missed the logic then :( – Jean-François Fabre Sep 12 '16 at 21:33
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@Jean-FrançoisFabre: the initialization logic is simple, *if any value of any member is initialized, then all other values not expressly initialized to some value, are initialized to zero by default* `.c={5};` is equivalent to `.c={5,0,0,0,0};` and `.c={5,5};` is equivalent to `.c={5,5,0,0,0};` – David C. Rankin Sep 12 '16 at 22:06

score 0 · Answer 2 · edited May 23 '17 at 11:51

0

OP has 3 goals: 1) field array size is fixed width, 2) initialization like {7,7,7,7,7} is fixed width, 3) c to a non-zero value. As #1 and #2 have their sizes independent coded, 2 of the 3 goals can be met, but not all 3 - that is tricky.

What is to prevent/warn about MY_STRUCT_T my_struct = {.c = {5,5,5,5,5}}; not meeting goals should uint32_t c[5]; later become uint32_t c[6];? Nothing really.

Lacking a maintainable coding paradigm, consider this - copy one by one

edited May 23 '17 at 11:51

Community

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answered Sep 12 '16 at 23:25

chux - Reinstate Monica

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Yes, the summary is correct. That linked idea is not idea because I actually have to call that `for` loop code segment. – Frederick Sep 13 '16 at 18:12

Initializing an array member of a struct by name

2 Answers2