How to validate in gcc that variable is used with hton in certain function

Question

I defined uint16 variable. I want to have a validation in compilation that whenever this variable is used, it must be first transformed with hton(). Is there a way to validate it during gcc compilation?

Thanks.

Answer 1

Not directly, no, I don't believe.

I believe the proper solution to this is ordinary abstraction. Set up a file that contains your variable, together with getter and setter routines:

/* var.c */

static uint16_t my_hidden_var;

void set_hidden_var (uint16_t v) {
  my_hidden_var = v;
}

uint16_t get_hidden_var (void) {
  return htons (my_hidden_var);
}

Obviously that's a simplistic example, and you'd probably want to add more, but the point is that your access requirements are enforced.

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If that's too heavyweight, I'd create a macro as the getter (an inline function would work fine too):

#define GET_VAR() htons (var)

Then, any mention of "var" in your sources must be either incorrect, or an exception to the rule, and you can find them easily with a simple text search.

Answer 2

I don't think there is a proper solution to this in C, as there is no way we can verify that a variable has changed byte order by going through hton().

If somehow we are able to verify that, we could use a static assert (talked about here and here) and create compile time checks.

You could still write a macro after the declaration of your variable var:

#define var hton(var)

This is probably a bad solution and could mess things up, so just use a function which returns the variable after running it through hton().