struct member array size based on const int across files

Question

So I want to have a definition of the size of an array within a struct known at compile time. I would also like that number available as a variable for ease of use later. What I have is the following:

const int BANANA_ARRAY_SIZE = 10;

typedef struct
{
  char bananas[BANANA_ARRAY_SIZE];
  int some_other_stuff;
} banana_struct;

This functions fine. However, if I have it in a .h file that gets included in multiple places, the compiler complains about redefinition of BANANA_ARRAY_SIZE (which makes sense). So I need to declare it as an extern so multiple compilation units can know about it.

So, I now have

extern const int BANANA_ARRAY_SIZE;

typedef struct
{
  //.. same as before
} banana_struct;

and in an implementation file I have

const int BANANA_ARRAY_SIZE = 10;

But now the compiler won't let me define the struct anymore with complaints of

fields must have a constant size: variable length array in structure

Is there any way I can achieve what I want (have length of array stored in variable and used to define struct)?

Edit:

In response to the suggestions to instead use #defines, I'd rather not.

My question is about how to have this constant value stored in a variable and also used to set the length of an array in a struct. If you need further justification, assume I need a function that takes a pointer to an int. Can't take a reference of a #define.

Answer 1

In C language const object is not a constant. You cannot use it to declare a non-VLA array. Your first declaration is not compilable in C language, which makes it unclear what you mean by "functions fine".

See here for more details: Shall I prefer constants over defines?

In your case you are restricted to either #define or enum constants. If you also want to create pointers to that value, you will have to additionally declare a const object with the same value, either globally or locally as needed. But you won't be able to use it in non-VLA array declarations. Instead, you will have to use the #define or enum constant. E.g.

// In .h file
#define BANANA_ARRAY_SIZE 10
extern const int BANANA_ARRAY_SIZE_OBJ;

// In .c file
const int BANANA_ARRAY_SIZE_OBJ = BANANA_ARRAY_SIZE;

Answer 2

You can either use a enum or a #define

enum {
BANANA_ARRAY_SIZE = 10
};

or

#define BANANA_ARRAY_SIZE 10