initialize inner struct as constant in outer struct initialization

Question

I have a struct inside a struct and on initialization of the outer struct I want to initialize the inner struct as const.

typedef struct A {
  uint16_t id;
}A;

typedef struct B {
  A a;
  uint16_t data;
}

I know I can initialize the inner struct when initializing the outer struct by this code:

B test = {
  {
    .id = 0x100
  },
  .data = 0
};

I know I can do it this way:

const A aTest = {
  .id = 0x100
};
B test = {
  .a = aTest,
  .data = 0

But is there a way to make the inner initialization directly constant?

What do you mean by "make this inner initialization constant"? Can you please elaborate? — Some programmer dude
– Some programmer dude, Commented Jun 27, 2016 at 13:19
Possible duplicate of How to initialize a struct in accordance with C programming language standards — wigy
– wigy, Commented Jun 27, 2016 at 13:20
Do you mean that B test = { .data = 0 }; should set test.a.id implicitly to 0x100? — user694733
– user694733, Commented Jun 27, 2016 at 13:22

dbush · Accepted Answer · 2016-06-27 13:20:35Z

1

You need to define the inner member as const:

typedef struct B {
  const A a;
  uint16_t data;
} B;

Then you can initialize like this:

B test = {
  {
    .id = 0x100
  },
  .data = 0
};

While this generates a compiler error:

test.a.id=1;

answered Jun 27, 2016 at 13:20

dbush

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