The standard doesn't defined well-formedness, nor does it consider undefined behaviour illegal necessarily. It simply has nothing to say about what happens when undefined behaviour is invoked.
And it is OK to invoke it if you know what your implementation will do. The standard even gives documenting the behaviour as an option.
(I wonder how many people worry about supplying clang a file that doesn't end in a new line? That is undefined behaviour, and yet you know exactly what's going to happen: you'll get a warning, if compilation continues the code will build as if the new line were there, and clang won't delete your source file, even though it would be perfectly within its rights to.)
> clang won't delete your source file, even though it would be perfectly within its rights to.
UB allows the execution of the compiled program to wipe your hard drive, but it certainly does not give your compiler that right. I mean, the standard doesn't say what side effects invoking a compiler is allowed to have (because that's out of scope), so none of it can be predicated on UB.
Thanks for the clarification. An outbreak of good sense? I hope it's contagious. It is still undefined behaviour in C11.
Not sure I agree with you about UB - missing line-endings is a parse-time issue, so the intent appears to be that the compiler (or interpreter) is free to do what it likes even at this stage, before your program is even ready to run.
And it is OK to invoke it if you know what your implementation will do. The standard even gives documenting the behaviour as an option.
(I wonder how many people worry about supplying clang a file that doesn't end in a new line? That is undefined behaviour, and yet you know exactly what's going to happen: you'll get a warning, if compilation continues the code will build as if the new line were there, and clang won't delete your source file, even though it would be perfectly within its rights to.)