[Chris_Newton]

But the last version with major changes was C11, nearly a decade ago. Even that was almost entirely backward-compatible, other than a few very specific cases like removing the inherently dangerous `gets` function from the standard library. And even that removal followed formal deprecation several years earlier, and widespread advice not to use it at all for many years before that.

Put another way, while the C language has evolved, you can still compile C code written several decades ago using modern tool chains with an excellent chance of having it work immediately or at worst needing some very minor changes.

It’s depressing that some of the comments in today’s discussion are praising Clojure because code often still works after 5 years. Obviously that is itself a good thing, but is only 5 years now a remarkably long time for code to still work?

[pjmlp]

Actually no, because C11 has removed features from C89 and C99, while C17 has done some UB "improvements".

[Chris_Newton]

There is very little that has changed that isn’t backward compatible, though, and what there is has mostly been in areas that no sensible programmer should ever have relied on in more than toy programs anyway, like inherently unsafe functions or undefined behaviour. You probably have to go back to C99 prohibiting some things that used to be implicit and therefore to code written over two decades ago to find “real” exceptions to that. Compared to many “modern” languages, I’d say that’s still an excellent track record for longevity and compatibility.

[pjmlp]

Toy programs like Linux kernel, once an heavy user of VLAs, which only GCC and clang ever implementated, while everyone else just moved from C89 to C11 without ever caring about them.

[Chris_Newton]

Sorry, I’m not sure I’m understanding your point here. Are you claiming that variable length arrays have been removed from C in recent standards after they were added in C99? Or is your objection that some compilers are very slow to support language features even after they have been standardised? Or something else?

[pjmlp]

I am not claiming, it is a fact.

It was dropped from C11, moved into optional annexes and all commercial compilers that were yet to be fully C99 compliant just moved to C11 instead, without bothering with optional annexes.

The world of C compilers isn't only GCC and clang.

[Chris_Newton]

Something being dropped is not the same as making something optional. In this case, the latter action was an explicit recognition of the reality that many compilers never fully implemented the previous standard anyway.

The point here was about backward compatibility. What standard C99 code is not also standard C11 code? What used to compile a few years ago but won’t compile today? We all understand that there are some minor exceptions, but I think it’s fair to say the answer to both question is not much.