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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: this girl calls c ugly
Date: Fri, 05 Jun 2026 05:49:58 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> James Kuyper <jameskuyper@alumni.caltech.edu> writes:
> [...]
>
>> One advantage of having a single program do the whole thing, is
>> that error messages can mention the actual text of the line where
>> a problem was detected, without any pre-processing applied.
>
> Typical preprocessors emit directives that tell the compiler
> about the current file name and line number, precisely so that
> diagnostic messages can refer to the original text.
>
> For example:
>
> $ cat hello.c
> #include <stdio.h>
> int main(void) {
>     printf("Hello world!\n");
> }
> $ gcc -E hello.c | tail
> extern int __uflow (FILE *);
> extern int __overflow (FILE *, int);
> # 983 "/usr/include/stdio.h" 3 4
>
> # 2 "hello.c" 2
>
> # 2 "hello.c"
> int main(void) {
>     printf("Hello world!\n");
> }
> $
>
> The line `# 2 "hello.c"` is, according to the C standard, a
> "non-directive", which is a kind of directive.  Executing a
> non-directive has undefined behavior, 

Since it is gcc that is generating the non-directives, for
internal purposes, and gcc that is consuming them, it hardly
seems worth worrying about whether their behavior is defined
or not.