How to initialize a const variable inside a struct in C?

Question

I write a struct

struct Tree{
    struct Node *root;
    struct Node NIL_t;
    struct Node * const NIL;    //sentinel
}

I want

struct Node * const NIL = &NIL_t;

I can't initialize it inside the struct. I'm using msvs.

I use C, NOT C++. I know I can use initialization list in C++.

How to do so in C?

Answer 1

If you are using C99, you can used designated initializers to do this:

struct Tree t = { .root = NULL, .NIL = &t.NIL_t };

This only works in C99, though. I've tested this on gcc and it seems to work just fine.

Answer 2

For those seeking a simple example, here it goes:

#include <stdio.h>

typedef struct {
    const int a;
    const int b;
} my_t;

int main() {
   my_t s = { .a = 10, .b = 20 };
   printf("{ a: %d, b: %d }", s.a, s.b);
}

Produces the following output:

{ a: 10, b: 20 }