Undefined behavior[1]
> #define assert(c) while (!(c)) __builtin_unreachable()
Undefined behavior[1]
> I’ll cast away the const if needed.
Undefined behavior[2]
> The assignments are separated by sequence points, giving them an explicit order.
I don't believe assignments are sequence points and only the function call is.
[1] https://en.cppreference.com/w/c/language/identifier#Reserved...
> Undefined behavior[2]
How so? As the page you linked mentions, simply casting 'const T *' to regular 'T *' is well-defined; it's only modifying a const object through the pointer that's UB (C17 6.7.3/7).
> I don't believe assignments are sequence points and only the function call is.
Assigments within expressions don't create sequence points. However, the expression of an expression statement is a full expression (i.e., not a subexpression of another expression), and there is a sequence point between each pair of full expressions (C17 6.8/4). In other words, the semicolons create sequence points.
> Undefined behavior[2]
To be clear, it's only UB if the object was defined const, which is the case given he wrote:
> One small exception: I still like it as a hint to place static tables in read-only memory closer to the code. I’ll cast away the const if needed.
So you are correct on this point. Funnily enough, such objects are relatively rare IME, so I had to double-check to see that he was advocating it specifically in the rare case where it must not be applied.
And people keep telling me that nobody uses the C preprocessor to define their own syntax any more!
Given that this particular undefined behavior usually causes crashes in practice, I expect the author is talking about casting away the const but not actually writing to the pointer. Which is legal.
My spidey senses tingle whenever I see const-ness cast away because it almost always means something is wrong. Either a function is missing a qualifier on an argument, or something very unsafe is happening. Why force callers to cast away const-ness in hopes that everything will be fine when you can just write the correct function signature.
And that is legal.