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Suppressing "Parameter not used" Warning

Started by Dave Hansen October 3, 2005
Alexei A. Frounze wrote:
> "Thad Smith" <ThadSmith@acm.org> wrote in message > news:4341e5ff$0$27319$892e0abb@auth.newsreader.octanews.com... > ... > >>I have used a void cast for some compilers. For another, I was >>successful with >> >>#define UNUSED(x) if(x); > > > Nice, though some clever compiler could warn here whether or not you're sure > it's what you intend to do, whether or not this code has any effect.
Of course. The compiler in question (an old Keil compiler) gave a warning for the void cast. I experimented and found that if(x);; (another semicolon added after the macro invocation) generated no code and no warning for that compiler. With no standard way to do this, we are left to search about for implementation-dependent hacks. Thad
Thad Smith <ThadSmith@acm.org> writes:

[suppressed "parameter not used" warnings]
> With no standard way to do this, we are left to search about > for implementation-dependent hacks.
Personally, I use an implementation-dependent feature that works for the compilers I really care about. Why worry about trying to suppress warnings on every compiler? It's not possible and you could waste a lot of time trying. -- "Large amounts of money tend to quench any scruples I might be having." -- Stephan Wilms
On 2005-10-05, Ben Pfaff <blp@cs.stanford.edu> wrote:
> Thad Smith <ThadSmith@acm.org> writes: > > [suppressed "parameter not used" warnings] >> With no standard way to do this, we are left to search about >> for implementation-dependent hacks. > > Personally, I use an implementation-dependent feature that > works for the compilers I really care about. Why worry about > trying to suppress warnings on every compiler? It's not > possible and you could waste a lot of time trying.
Here in comp.arch.embedded, anybody with too strong an aversion to implementation-dependent "hacks" is in for a lifetime of frustration. There are just too many times when there simply is no other way to accomplish that which must be accomplished. Sure, standard and portable is always a good goal, but when theres a 90+ percent chance the program is never going to be compiled by a different compiler or run on a different platform, there's a limit to how much utility should be sacrificed and much effort should be expended to avoid usign somethign like gcc's __attribute__(()) extension. -- Grant Edwards grante Yow! My LIBRARY CARD at expired... visi.com
Ben Pfaff wrote:
> > Thad Smith <ThadSmith@acm.org> writes: > > [suppressed "parameter not used" warnings] > > With no standard way to do this, we are left to search about > > for implementation-dependent hacks. > > Personally, I use an implementation-dependent feature that works > for the compilers I really care about.
Same here.
> Why worry about trying to suppress warnings on every compiler?
I don't know. I'm certainly not advocating such worry.
> It's not possible and you could waste a lot of time trying.
True. I typically only work with a few compilers and spend a little time to customize such things as eliminating unneeded warnings, which allows me to more easily find real problems. Turning off warnings, ignoring them, or sprinkling non-standard code throughout is a last resort for me. You may have other techniques that work better for you. Thad
In article <1128616135.46050bff8a89745339c73052e1094284@teranews>,
Thad Smith  <ThadSmith@acm.org> wrote:
>Ben Pfaff wrote: >> >> Thad Smith <ThadSmith@acm.org> writes: >> >> [suppressed "parameter not used" warnings] >> > With no standard way to do this, we are left to search about >> > for implementation-dependent hacks. >> >> Personally, I use an implementation-dependent feature that works >> for the compilers I really care about. > >Same here. > >> Why worry about trying to suppress warnings on every compiler? > >I don't know. I'm certainly not advocating such worry. > >> It's not possible and you could waste a lot of time trying. > >True. I typically only work with a few compilers and spend a little >time to customize such things as eliminating unneeded warnings, which >allows me to more easily find real problems. Turning off warnings, >ignoring them, or sprinkling non-standard code throughout is a last >resort for me. You may have other techniques that work better for >you.
Indeed there is a much better technique. Make clean code. Catch the warnings in a file. Carefully inspect the warnings and head them. Catch the warnings on the resulting cleaner code. Now in the regression test, expect the warnings to remain the same, i.e. make a diff with the file with the warnings of the previous test. Only act on warnings changes, indicative of new warnings. Or on warnings that went away since you cleaned up your code. Never ever becludge your code to suppress warnings. They are there to ... warn you, which is a Good Thing.
> >Thad
-- -- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- like all pyramid schemes -- ultimately falters. albert@spenarnc.xs4all.nl http://home.hccnet.nl/a.w.m.van.der.horst
Albert van der Horst <albert@spenarnc.xs4all.nl> wrote:

# Indeed there is a much better technique.
# Make clean code. Catch the warnings in a file.

Recompile megabytes of source code because you change one
function declaration in a header file.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
Raining down sulphur is like an endurance trial, man. Genocide is the
most exhausting activity one can engage in. Next to soccer.
Albert van der Horst wrote:
> > In article <1128616135.46050bff8a89745339c73052e1094284@teranews>, > Thad Smith <ThadSmith@acm.org> wrote:
> >True. I typically only work with a few compilers and spend a little > >time to customize such things as eliminating unneeded warnings, which > >allows me to more easily find real problems. Turning off warnings, > >ignoring them, or sprinkling non-standard code throughout is a last > >resort for me. You may have other techniques that work better for > >you. > > Indeed there is a much better technique. > Make clean code. Catch the warnings in a file. > Carefully inspect the warnings and head them. > Catch the warnings on the resulting cleaner code. > Now in the regression test, expect the warnings to remain > the same, i.e. make a diff with the file with the warnings > of the previous test. > Only act on warnings changes, indicative of new warnings.
That's an interesting idea! I suppose I should strip the line numbers on the warnings so that code insertion/deletion doesn't trigger an avalanche in the diff. It's time for a little scripting. I'll have to give that a try. I could even fail a make if the warning file changed.
> Or on warnings that went away since you cleaned up your code.
Hmmm, the ominous disappearing warning!
> Never ever becludge your code to suppress warnings.
The goal, of course, is to easily detect new warnings so that they can be examined. Your approach is an interesting one.
> They are there to ... warn you, which is a Good Thing.
Well, yes. That's why I try to hint to the compiler that its OK that an if statement has a constant expression (because the macro it is in takes various parameters). Let's see, if I have conditional sections in my code, the warnings may come and go as I change switches -- oh, dear! I suppose I should have to have a separate expected warnings file for each configuration. Thad
In comp.lang.c Thad Smith <ThadSmith@acm.org> wrote:
> Albert van der Horst wrote:
[snip]
>> Make clean code. Catch the warnings in a file. >> Carefully inspect the warnings and head them. >> Catch the warnings on the resulting cleaner code. >> Now in the regression test, expect the warnings to remain >> the same, i.e. make a diff with the file with the warnings >> of the previous test. >> Only act on warnings changes, indicative of new warnings. > > That's an interesting idea! I suppose I should strip the line numbers > on the warnings so that code insertion/deletion doesn't trigger an > avalanche in the diff. It's time for a little scripting. I'll have > to give that a try. I could even fail a make if the warning file > changed.
This idea has been wandering around me for some time, too. It could work like this: programmer puts #pramas in the code, which contain verbatim quotes (or regexes, or identifires) of warnings that are to be suppressed for the next line. The utility program (or a script) calculates line numbers and produces a list of warnings (with the line numbers) to cut out from the compiler output. Like this: #pragma nowarn t.c:%n: warning: comparison between signed and unsigned if (u>s) -- Stan Tobias mailx `echo siXtY@FamOuS.BedBuG.pAlS.INVALID | sed s/[[:upper:]]//g`

S.Tobias wrote On 10/13/05 17:19,:
> In comp.lang.c Thad Smith <ThadSmith@acm.org> wrote: > >>Albert van der Horst wrote: > > [snip] > >>>Make clean code. Catch the warnings in a file. >>>Carefully inspect the warnings and head them. >>>Catch the warnings on the resulting cleaner code. >>>Now in the regression test, expect the warnings to remain >>>the same, i.e. make a diff with the file with the warnings >>>of the previous test. >>>Only act on warnings changes, indicative of new warnings. >> >>That's an interesting idea! I suppose I should strip the line numbers >>on the warnings so that code insertion/deletion doesn't trigger an >>avalanche in the diff. It's time for a little scripting. I'll have >>to give that a try. I could even fail a make if the warning file >>changed. > > > This idea has been wandering around me for some time, too. > It could work like this: programmer puts #pramas in the code, > which contain verbatim quotes (or regexes, or identifires) of warnings > that are to be suppressed for the next line. The utility program (or > a script) calculates line numbers and produces a list of warnings > (with the line numbers) to cut out from the compiler output. > Like this: > #pragma nowarn t.c:%n: warning: comparison between signed and unsigned > if (u>s)
Ugh. Ugh ugh ugh. First, while the use of warning-suppressing tags in the code goes back at least to lint, using #pragma to express them is a truly terrible idea. Somewhere there'll be a compiler that actually recognizes "#pragma nowarn" and does something with it -- for example, suppressing all warning messages for the entire translation unit, or turning on ARN (automatic name rewriting) NOW. Embed such tags in specially-formatted comments that are linquistically inert, not in constructs that might at any moment turn into toxic chemicals and rot your program. (Aside: I quite understand that the idea of "a different compiler" may well be foreign to many projects of interest in comp.arch.embedded. However, the thread is cross-posted to comp.lang.c as well, where portability concerns appear to carry somewhat more weight.) Second, a far better way to suppress the warning you mention is if (u > (unsigned)s) Sometimes it can be a bad thing for a "last resort" mechanism to exist: it's too easy for people to give up searching for the "first resort." Finally, and it's been said before: The goal of turning of ALL warnings from ALL compilers is ultimately futile, because compilers are allowed to complain about anything they feel like. "Warning: Source was modified at 2:37 AM; sleep-deprived programmer may have made more mistakes than usaul." -- Eric.Sosman@sun.com
In comp.lang.c Eric Sosman <eric.sosman@sun.com> wrote:
> S.Tobias wrote On 10/13/05 17:19,: >> In comp.lang.c Thad Smith <ThadSmith@acm.org> wrote: >>>Albert van der Horst wrote: >> >> [snip] >>>>Make clean code. Catch the warnings in a file. >>>>Carefully inspect the warnings and head them. >>>>Catch the warnings on the resulting cleaner code. >>>>Now in the regression test, expect the warnings to remain >>>>the same, i.e. make a diff with the file with the warnings >>>>of the previous test. >>>>Only act on warnings changes, indicative of new warnings. >>>That's an interesting idea! I suppose I should strip the line numbers >>>on the warnings so that code insertion/deletion doesn't trigger an >>>avalanche in the diff. It's time for a little scripting. I'll have >>>to give that a try. I could even fail a make if the warning file >>>changed. >> This idea has been wandering around me for some time, too. >> It could work like this: programmer puts #pramas in the code, >> which contain verbatim quotes (or regexes, or identifires) of warnings >> that are to be suppressed for the next line. The utility program (or >> a script) calculates line numbers and produces a list of warnings >> (with the line numbers) to cut out from the compiler output. >> Like this: >> #pragma nowarn t.c:%n: warning: comparison between signed and unsigned >> if (u>s) > > Ugh. Ugh ugh ugh. >
That's how great ideas die - someone says "ugh"... ;-)
> First, while the use of warning-suppressing tags in the > code goes back at least to lint, using #pragma to express > them is a truly terrible idea. Somewhere there'll be a > compiler that actually recognizes "#pragma nowarn" and does > something with it -- for example, suppressing all warning > messages for the entire translation unit, or turning on > ARN (automatic name rewriting) NOW.
:-)
>Embed such tags in > specially-formatted comments that are linquistically inert, > not in constructs that might at any moment turn into toxic > chemicals and rot your program. >
That's true. All #pragmas (with a small exception) suffer from this disease. OTOH the whole concept is subject to implementation behaviour and is not (universally) portable. But I agree, it's always better to avoid a mine-field, and take a quiet and safe path. (Only, what if the compiler uses the same tags embedded in comments for its own purposes, too?) What might actually be bad in practice with #pragmas is that a compiler might issue warnings about unrecognized #pragmas, thus we'd be chasing our tail. Let's make that: /* $ nowarn: ... $ */ (Actually, only `$ nowarn: ... $' part is recognized by the utility.)
> Second, a far better way to suppress the warning you > mention is > > if (u > (unsigned)s) > > Sometimes it can be a bad thing for a "last resort" mechanism > to exist: it's too easy for people to give up searching for > the "first resort." >
That was just a poor example how it could be used. Anyway, you had to clutter the code to suppress the warning, too. Sometimes there's no way of "fixing" warnings for all compilers, you do it for one, and some other issue arises for another. Consider this (semi-real-life example): off_t off; size_t siz; if (siz > off) ; may cause: warning: signed/unsigned in comparison on one implementation, whereas if (siz > (size_t)off) ; on another may issue: warning: possible loss of data in cast (besides that casting always makes me feel uneasy). It's not obvious which side to cast to which. (I actually solved it this way (through a macro): if(siz + (off_t)0 > off + (size_t)0) ; (clue: usual arithmetic conversions). )
> Finally, and it's been said before: The goal of turning > of ALL warnings from ALL compilers is ultimately futile, > because compilers are allowed to complain about anything > they feel like. "Warning: Source was modified at 2:37 AM; > sleep-deprived programmer may have made more mistakes than > usaul." >
Well, yes, but my goal is not to turn off ALL warnings, but only *known* and *inspected* warnings. The idea is that I don't waste my work when line numbers change. -- Stan Tobias mailx `echo siXtY@FamOuS.BedBuG.pAlS.INVALID | sed s/[[:upper:]]//g`