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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: // comments and \
Date: Tue, 01 Dec 2015 09:21:12 -0800
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BartC <bc@freeuk.com> writes:
> This is a problem I came across with an assembler, which caused me some 
> trouble to sort out.
>
> Then I thought I'd try it with C, convinced it couldn't be as silly, but 
> apparently it was!
>
> Here:
>
>    // this is a comment ... \
>        puts("Hi!");
>
> the continuation character at the end of the comment means the following 
> line isn't compiled (which can give puzzling results as you can imagine).
[...]

It's actually a bit worse than that.  Consider this program:

    #include <stdio.h>
    int main(void) {
        // \ 
        puts("This is a comment");
        puts("This is not a comment");
    }

You can't see it, but there's a space after the backslash on line 3
(assuming it's not stripped by somebody's news software).  Because the
line doesn't end with a backslash, it's not a continuation line, so the
output *should* be:

    This is not a comment

tcc produces that output, but both gcc and clang ignore the trailing
blank and produce this output:

    This is a comment
    This is not a comment

(clang warns about the trailing space.)

I prefer the gcc/clang behavior, but it's not consistent with the
standard -- though I suppose you could argue that the trailing blanks
could be removed in translation phase 1.

In any case, the solution is straightforward: Don't Do That.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"