From: Erik Max Francis <max AT alcyone DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Warning control. Is there more convenient way?
Date: 23 Oct 1997 07:08:40 GMT
Organization: Alcyone Systems
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References: <AD7EoFq8hO AT rsuzi DOT pgu DOT karelia DOT ru>
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Roman Suzi wrote:

> What can I add to suppress them in GCC, so that
>  - I shall not receive another kind of warning;
>  - the effectiveness of the code will remain the
> same (no additional commands will be inserted for dummy
> usage of the variables) ?

You have three options:

First, if you're using C++ (you mentioned both C and C++), then you can
leave off the argument name, viz.

    int f(void *a, int b, double /* unused */)
    {
        ...
    }

In both languages, you can use them in a dummy expression which has no
effect:

    int f(void *a, int b, double unused)
    {
        (void) unused;

        ...
    }

This creates an extra statement, but a good compiler (and I'm sure gcc
qualifies, though I haven't actually checked myself) will optimize it
out, leaving you with no extra code.  Though this might cause the
compiler to emit "code has no effect" warnings.

A final, less ideal option, is simply to name the argument `unused'. 
That way you can look at the warnings emitted at a glance and decide
whether or not they're ones you didn't anticipate or not.

> I think the author of DJGPP can easily include
> along INCLUDE warning checkboxes the EXCLUDE
> warning ones: so it will be much easier to
> check just 'Wall' and a few of unwanted warnings.

See the Warning Options node of the info gcc page, where it lists each
warning and what command-line option to provide to remove it.  (I am
guessing you're using RHIDE, or somesuch, since DJGPP doesn't have
"checkboxes.")  Specifically:

    `-Wunused'
     Warn whenever a variable is unused aside from its declaration,
     whenever a function is declared static but never defined, whenever
     a label is declared but not used, and whenever a statement
     computes a result that is explicitly not used.

     To suppress this warning for an expression, simply cast it to
     void.  For unused variables and parameters, use the `unused'
     attribute (*note Variable Attributes::.).


Note, however, that this doesn't address _your_ problem, because you
want _some_ of the unused argument warnings to be suppressed, but others
to be emitted.

> Or are there any #pragma s  to do the trick?

There may be, though in my quick scan through the info pages I couldn't
find any.  The gcc maintainers tend to frown upon #pragmas, so they're
usually only provided for fairly limited circumstances.

-- 
          Erik Max Francis, &tSftDotIotE / mailto:max AT alcyone DOT com
                        Alcyone Systems / http://newton.alcyone.com/
   San Jose, California, United States / icbm://+37.20.07/-121.53.38
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   "After each war there is a little / less democracy to save."
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