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Comparison of Constant....

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Posted by Alyce   (43 posts)  [Biography] bio
Date Thu 08 Sep 2016 02:37 AM (UTC)
Message
This has been bugging me... It's not TOO big an issue I don't believe, but it's one that is causing the compile to not be nice using smaugfuss 1.9 and compiling with cygwin.


comm.c: In function ‘void nanny_get_name(DESCRIPTOR_DATA*, char*)’:
comm.c:1886:44: warning: comparison of constant ‘255’ with boolean expression is always false [-Wbool-compare]
    if( check_playing( d, argument, FALSE ) == BERR )
                                            ^
comm.c:1954:12: warning: comparison of constant ‘255’ with boolean expression is always false [-Wbool-compare]
    if( chk == BERR )
            ^
comm.c: In function ‘void nanny_get_old_password(DESCRIPTOR_DATA*, char*)’:
comm.c:2049:12: warning: comp


I did some research a while back and someone had posted how to change the code to remove those warnings.. and it did.. however when connecting to a link-dead player, it caused segmentation faults, so I just changed it back and haven't really bothered with it since...

Now i'm just about done adding what I wanted to to the code-base and changed it to suit my needs, but that one lingering issue is still bugging me.

Mud works fine with the warnings there.. no segfault on connecting to link-dead... I just want them gone.

has anyone else ran across this issue? if so, how did you resolve it?
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Posted by Fiendish   USA  (1,641 posts)  [Biography] bio   Global Moderator
Date Reply #1 on Thu 08 Sep 2016 06:05 PM (UTC)

Amended on Thu 08 Sep 2016 06:10 PM (UTC) by Fiendish

Message
So...

The C language didn't have a native bool type until C99. Before that, people would resort to stupid tricks like you can find in src/mud.h where it says
typedef unsigned char bool;
#define true 1
#define false 0


That means that the check_playing function in src/comms.c was created by a dickhead, because it declares that it semantically returns a boolean type but then actually returns three different unsigned chars (0, 1, 255). EXCEPT THAT IT ONLY DOES THIS IF __cplusplus IS NOT #DEFINED, but you wouldn't know that unless you went digging somewhere else (back in src/mud.h)! If _cplusplus *is* defined, then you have a function that actually returns a bool, and each of those "return BERR;"s is actually just returning true because anything not zero is true in C++. And then of course the compiler is then trying to convert those real booleans back into integers so that they can be compared against 255, except that true converts to 1 and false converts to 0, neither of which will equal 255. Sigh.

Getting that warning means that you're using a C++ mode compiler. You might try switching to a C compiler instead.

If I were going to fix this for real, I'd make check_playing declare that it returns unsigned char (or int) so that it stops converting into booleans instead of doing these only-sometimes-fake "bool" shenanigans.

https://github.com/fiendish/aardwolfclientpackage
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Posted by Alyce   (43 posts)  [Biography] bio
Date Reply #2 on Fri 09 Sep 2016 03:25 AM (UTC)
Message
well im compiling in cygwin for the moment. My bandwidth is severely limited right now so it's not possible to add any packages or change any. When I put it on an actual server with the proper libraries and stuff, I am assuming this will go away correct?
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Posted by Nick Gammon   Australia  (21,324 posts)  [Biography] bio   Forum Administrator
Date Reply #3 on Fri 09 Sep 2016 09:07 PM (UTC)
Message
No, I doubt it. How are you compiling? If you are using g++ you are compiling in C++ mode. If gcc then it is C mode. Also the suffix of your source file might affect it.

- Nick Gammon

www.gammon.com.au, www.mushclient.com
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Posted by Alyce   (43 posts)  [Biography] bio
Date Reply #4 on Sat 10 Sep 2016 01:15 AM (UTC)
Message

gcc-core                                5.4.0-1                          OK
gcc-g++                                 5.4.0-1                          OK
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Posted by Kasji   (35 posts)  [Biography] bio
Date Reply #5 on Sat 10 Sep 2016 05:25 AM (UTC)

Amended on Sat 10 Sep 2016 05:26 AM (UTC) by Kasji

Message
So, BERR is defined as the number 255.

check_playing() returns a bool.

In C, in Smaug, bool is type defined as an int or maybe short int. So check_playing() == BERR in C would be comparing 2 numbers.
[EDIT] Er, unsigned char like Fiendish said.

You're using C++ though, and as such, you're comparing a true/false from check_playing() to a number.

The change I made on my code was to change check_playing() from a bool return value to an int return value.

int check_playing(Blah blah blah)
{
Stuff
}
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Posted by Alyce   (43 posts)  [Biography] bio
Date Reply #6 on Sat 10 Sep 2016 05:38 AM (UTC)
Message
That is what I did at first to get rid of the warnings, and it worked to that extent.. however in doing so, when connecting to a link-dead player, or when logging on when connected it triggered segmentation faults.

It works just fine with the warnings there, it's just an eye sore when compiling.
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Posted by Kasji   (35 posts)  [Biography] bio
Date Reply #7 on Sat 10 Sep 2016 06:11 AM (UTC)
Message
I'm not running Smaug, so I can't say for sure how different our codes are, but... Recall that as a bool, check_playing will always evaluate as false. It's possible that something inside the if statement block is causing the crash, but it never happens while check_playing returns a bool because that block never gets executed (due to the if statement always evaluating as false).
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Posted by Alyce   (43 posts)  [Biography] bio
Date Reply #8 on Sat 10 Sep 2016 06:34 AM (UTC)
Message
I will be able to do more in depth looking with GDB but with my limited bandwidth I can't get it downloaded to my cygwin packages... I'll have to wait for a proper server
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Posted by Kasji   (35 posts)  [Biography] bio
Date Reply #9 on Sun 11 Sep 2016 10:38 PM (UTC)
Message
A trick that I use a lot when I don't have gdb available (for a while my mud wasn't dumping cores), is bug messages. I place bug messages around the area of code where the crash is happening, and can use that to narrow down the line that is causing the crash since I know the crash has to be happening before a bug message if it doesn't print out, or after a particular bug message if it does print out.
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