[account42]

Infinite loop without side effects == program stuck and not responding on user input and not outputting anything. That's not something a useful program will ever want to do.

[Certhas]

Not true, C++ made it so trivial infinite loops are not UB because it turns out they do have legitimate uses.

https://lists.isocpp.org/std-proposals/2020/05/1322.php

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p28...

[account42]

Yes, the C++ committee has been making some stupid decisions lately. This is not the only one.

Low level platform-specific code that needs to hot spin until an interrupt happens can use assembly for that part which it will need to do for the interrupt handler anyway.

[TuxSH]

You don't even need to use assembly for this, the wait for interrupt typically involves side effects.

[xigoi]

The problem is when you accidentally write an infinite loop. In a different language, you run the code, see that it gets stuck and fix it. In C, the compiler may delete the function, making it hard to realize what is happening.

[account42]

This is not a problem that C or C++ programmers actually encounter, ever.

[ncruces]

I actually encountered it a couple weeks ago.

Can you spot the infinite loop in this function?

  char* strcpy(char* restrict d, const char* restrict s) {
    stpcpy(d, s);
    return d;
  }

I'll help. A call to `stpcpy` that ignores the return value can be swapped with a call to the (more likely to be optimized) `strcpy`. Since that's infinite recursion, and there is no forward progress, it's undefined behavior and anything goes.

This isn't just theory, it actually broke things in practice for me.

[rssoconnor]

Naming an externally linked function with the prefix "str" is by itself UB since that prefix is reserved for <string.h>.

[ncruces]

Right. I am doing a standard library replacement, and forgot I needed to compile freestanding. Oops. My bad.

So `str` and `mem` are reserved. But then so are `to` and `is` (by <ctype.h>). Just forget about having a function named `is_valid_user`.

And so are `mtx_`, `cnd_`, `thrd_`, `atomic_`, `memory_`...

Which is why... everything in C is UB.

[1718627440]

Note, that this is not true for C.

[zarzavat]

https://9p.io/sources/plan9/sys/src/libc/9sys/abort.c

[account42]

This is already UB without an infinite loop.