Comment by wang_li

Write once run anywhere? But C already is a "write once run anywhere" language! Though, you usually have to recompile first :)

The criticisms related to UB are not about understanding the target platform and the target compiler's behavior. Undefined Behavior is not the same thing as Implementation-defined Behavior, and lots of folks (including me) would be satisfied with reclassifying chunks of UB as the latter.

The behavior of the target platform isn't really the issue. C23 mandates two's complement for signed integers. Most hardware wraps on overflow, but that literally doesn't matter. The standard says a program exhibiting signed overflow is undefined, period.

In practice, UB rules mean the compiler is free to remove checks for signed overflow/underflow, checks for null pointers, etc. This can and does happen. Man, just a few weeks ago, I just had to deal with a crash in a C program that turned out to be due to the compiler removing a null check. That was a painful one.

The point of this post, though, is even something as simple as "give me this string as an integer" doesn't have an answer that doesn't come with "are you OK with this best effort parse under these edge cases? Oh and we use this number as error, so you can't parse that".

Like… edge cases? It's parsing a number! We're not talking about I/O on hard vs soft intr NFS mounts, here. There's a right answer.

strlen(), on valid null terminated strings, doesn't come with caveats like "oh we can't measure strings of length 99".

But sure, C is turing complete. It is possible to solve any problem a turing machine can solve.

> understand the target platform and the target compiler’s behavior.

This is neither. This is purely the language.

isn't the whole point of C that it's portable assembly though? needing to understand the target platform/compiler's behavior to write correct code seems to cut against that claim quite a bit.