Re: Concatenated if and preprocessor

On 14/03/2025 21:10, Keith Thompson wrote:

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

Richard Harnden <richard.nospam@gmail.invalid> writes:

On 14/03/2025 16:44, Tim Rentsch wrote:

    for(  int just_once = 1;  just_once;  just_once = 0  ){

>
Any reason not to say ...
>
do {
     ...
} while (0);
>
... ?

>
In fact using do/while(0) is what I first wrote.  But then
I thought, oh wait, what if an overzealous compiler gives
a warning because the while() expression is always false? :-/

That would break a lot of macros :)

>
It's because of examples like this that I am wary of rules
like "enable all warnings" and "treat any warning condition
as an error."  I recently ran across a set of coding standard
rules that included these rules:  not just /some/ warning
conditions, but ALL warning conditions.  I still don't know
if they were literally serious.  (And my understanding is
clang has a -Weverything option, which enables all warning
conditions that clang is able to test for, no matter how
silly.)

 I've worked under such coding standards.  Perhaps surprisingly, I
haven't found them to be terribly inconvenient.  I rarely ran into
a warning that was inordinately difficult to avoid.   I can see that
"clang -Weverything" would cause problems.
 The most common inconvenience was that if I experimentally commented
out some code, and it caused some variable not to be referenced,
the build would fail.  (I could just add `(void)foo;` to avoid that.)
To be clear, this was not code that I intended to commit.
 I can imagine that there could be problems if a newer version of the
compiler produced new warnings, but we didn't often change compilers.
 (In one obscure case, I wrote a wrapper script that could be
installed in $PATH as "gcc" that would invoke the real gcc and
filter out a particular warning.  The wrapper was necessary due to
the behavior of a build script, not to an explicit coding standard.)
 

Hmm, clang with -Weverything is okay with:
   do { ... } while (0);
But not with:
   if ( 0 ) { ... }
But it's okay with:
   if ( (0) ) { ... }
I didn't know that was a thing, so I've learnt something new today, thanks.