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Wireshark-dev: Re: [Wireshark-dev] error: logical && with non-zero constant will always evaluat

From: Jeff Morriss <jeff.morriss.ws@xxxxxxxxx>
Date: Fri, 04 Jan 2013 09:01:51 -0500
Guy Harris wrote:
On Jan 3, 2013, at 1:40 PM, Jeff Morriss <jeff.morriss.ws@xxxxxxxxx> wrote:

Jeff Morriss wrote:
My (Fedora 10) gcc 4.3.2 was also generating this warning; it would seem that a fair spread of gcc versions seem to have the problem.
I added a configure check to stop using -Wlogical-op if the compiler is generating this warning in r46916.
Interestingly the Ubuntu buildbot says it would also get the warning:

checking whether we can add -Wlogical-op to CFLAGS... yes
checking whether -Wlogical-op generates warnings from strchr()... yes

Which means that

	#include <string.h>
int
	foo(char *sep, int c)
	{
	        if (strchr (sep, c) != NULL)
        	        return 1;
	        else
        	        return 0;
	}

	int
	main(int argc, char **argv)
	{
	        return foo(\"<\", 'a');
	}

fails to compile with the CFLAGS value at the time the test is done, plus -Werror; it could be failing for some other reason.  To quote the comment when I finally got it working for -Wshadow:

	Declare foo() before defining it - if we configure with
	--enable-extra-gcc-checks, given that we're building with -Werror (so
	that we find out whether the compiler issues a warning for a particular
	construct), we have to avoid constructs that will provoke *other*
	warnings.

so the code in question has to avoid whatever other warnings are being used, and the Ubuntu buildbot builds with --enable-extra-gcc-checks, so it warns about functions not declared with prototypes before they're defined.  I've checked in a change to declare foo() before it's defined; we'll see whether that fixes it.

Lesson to self: don't just be happy when 'configure' spits out the expected result. Instead look at config.log and see *why* I got the expected result... There were a bunch of other warnings in there which I didn't get when hand-compiling the program because I wasn't using all the options 'configure' was.