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Comment by smj-edison | Hacker News Reader

> Most of what gives high-reliability or high-assurance code that label is the process rather than the language.

This is what I've heard too. I have a friend who works in aerospace programming, and the type of C he writes is very different. No dynamic memory, no pointer math, constant CRC checks, and other things. Plus the tooling he has access to also assists with hitting realtime deadlines, JTAG debugging, and other things.

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> no pointer math

How does that work out? Does he never uses arrays and strings?

Like in most languages, with indexes.

But in C that's just syntax sugar for pointer math.

Except it is more obvious what is the intention, it is about clarity to the reader.

My point was indeed, that if you don't use pointer arithmetic in C, that means that you don't use arrays. I mean when you declare arrays of a fixed size, you can also declare an equivalent number of primitive variables instead, but I would find that inconvenient. Hence the question.

If I remember correctly, he meant that only array accesses are used, because their length can be checked (as all arrays have a static length due to no dynamic memory).

Indeed, this is what many people do. But even if you use dynamic memory, if you replace pointer arithmetic by array indexing, you get bounds checking. And in C this also works for arrays of run-time length.

But can't I put any pointer arithmetic in array brackets, so it wouldn't limit anything?

Whatever index you compute can be checked against a bound.

2[a*b] What bound?

This does not even compile. For array indexing,

array[expression]

if "array" has a bound whatever expression evaluates to can be checked against the bound of array. If "array" is not a bounded array but a pointer or an unbounded array, then this does not work, but my point is that it is easy to avoid such code.

It still makes it possible to have bounds checking. (And it is also not true anymore for C2Y.)

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