Very Computer

Hi all,

Even when I am using the option -Wall OR -Wunused, I am not warned
about unused variables (I deliberately introduce unused variables to
test the compiler ability to warn).
Any idea?

I am compiling C++ program with G++.

Thank you,
Mathieu Deziel

On 30 May 2001 05:05:42 -0700,

Quote:>Hi all,

>Even when I am using the option -Wall OR -Wunused, I am not warned
>about unused variables (I deliberately introduce unused variables to
>test the compiler ability to warn).
>Any idea?

Its ability to do so depend on the chosen optimization level.  The
information about unused variables is a side product of optimizing
the code.

Villy

To get that, I use:

g++ -O2 -Wall -W binaryoutfile -o sourcefile.c

Charles

You should probably discuss this with the GCC developers.  Try

--

Nate Eldredge

Quote:> > Even when I am using the option -Wall OR -Wunused, I am not warned
> > about unused variables (I deliberately introduce unused variables to
> > test the compiler ability to warn).

Ok, here was my problem: a tab at the end of a line in my makefile caused
the Makefile to be read incorrectly.  Thank you all for your help.

Quote:> > Its ability to do so depend on the chosen optimization level.
> > The information about unused variables is a side product of
> > optimizing the code.

Villy, I don't see how optimization would prevent some
warnings on the source code to be reported.  The "Unused variable" warning
relates to the source code itself, not to the compiled code (which,
with optimization turned on, might not reflect exactly the source code).
I haven't done any extensive tests, but changing the optimization level had
no impact on the warnings reported in my case.
Do you have some more details about it?  Am I missing something ?

Thank you, Mathieu.

But the *analysis* to determine whether something is unused is complex,
and is  usually a side-effect of the analysis required for optimization,
which is why you only get the desired warnings when optimization is
turned on.

Of course, you could argue that "-Wall" should turn on optimization, but
that's a bit of a stretch functionality-wise. Or maybe -Wall should turn
on the analysis for optimization, but in a "read-only" fashion that
doesn't actually change the generated code.  But that would be a major
structural change (read: major rewrite), so it's probably not practical.

Just accept it as a "hysterical" thing..
--
Shankar.

I think that Villy is thinking of the "uninitialized variable"
warning, for which this is true.  man gcc(1).

Micah