Date: Sun, 16 Mar 2008 22:29:34 -0700 From: Doug Hardie <bc979@lafn.org> To: Derek Ragona <derek@computinginnovations.com> Cc: freebsd-questions <freebsd-questions@freebsd.org> Subject: Re: C compiler issue perhaps? Message-ID: <59E2AE8C-70D4-49C8-B495-0F7CCCB042DB@lafn.org> In-Reply-To: <6.0.0.22.2.20080315075146.02610a20@mail.computinginnovations.com> References: <A768FF06-4601-42C6-A491-634F5135DCCD@lafn.org> <6.0.0.22.2.20080314171533.023f7c88@mail.computinginnovations.com> <511EC772-36FD-4799-B4A1-3AE690B6D048@lafn.org> <6.0.0.22.2.20080314202817.025de470@mail.computinginnovations.com> <EE488DB7-2E54-48F5-A3E2-1357BF848978@lafn.org> <6.0.0.22.2.20080315075146.02610a20@mail.computinginnovations.com>
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On Mar 15, 2008, at 05:59, Derek Ragona wrote:
> At 09:49 PM 3/14/2008, Doug Hardie wrote:
>
>> On Mar 14, 2008, at 18:31, Derek Ragona wrote:
>>
>>> At 06:56 PM 3/14/2008, Doug Hardie wrote:
>>>> There is no code running at that point. Its just sitting there
>>>> waiting for me to enter a gdb command.
>>>>
>>>>
>>>> On Mar 14, 2008, at 15:16, Derek Ragona wrote:
>>>>
>>>>> At 05:10 PM 3/14/2008, Doug Hardie wrote:
>>>>>> I have a program I was testing with gdb. I was trying to figure
>>>>>> out
>>>>>> why c.rmonths was always zero when it should have been 6.
>>>>>> Stepped
>>>>>> through using the gdb n command. Here is the output:
>>>>>>
>>>>>> (gdb)
>>>>>> 215 c.rmonths = (edate - tdate) /
>>>>>> toMONTHS;
>>>>>> (gdb)
>>>>>> 223 c.dial_in = u.dial_in[0];
>>>>>> (gdb)
>>>>>> 224 c.dsl = u.dsl[0];
>>>>>> (gdb) p c.rmonths
>>>>>> $1 = 0
>>>>>> (gdb) p c
>>>>>> $2 = {fa = 0, pwp = 0, disp_email = 0, imonths = 0, rmonths = 6,
>>>>>> type = 73 'I', cd = 0 '\0', dial_in = 82 'R', dsl = 0 '\0',
>>>>>> dsl_kit = 0 '\0', ip = 0 '\0', domain = 0 '\0', n_domain = 0
>>>>>> '\0',
>>>>>> renewal = 89 'Y', program = "I\000\000"}
>>>>>> (gdb) p c->rmonths
>>>>>> $3 = 6
>>>>>> (gdb) p c.rmonths
>>>>>> $4 = 6
>>>>>>
>>>>>>
>>>>>> Notice, the first time i print it its zero. The second time
>>>>>> its 6.
>>>>>> What gives here? I have seen this before but couldn't pin it
>>>>>> down.
>>>>>> The program is not compiled with any optimization. It is in a
>>>>>> shared
>>>>>> library though.
>>>>>
>>>>> It is hard to tell without the code you used. I would put some
>>>>> printf's in the code and see what and when that variable gets
>>>>> set to
>>>>> in actual running code.
>>>>>
>>>>> -Derek
>>>
>>> I understand it is waiting at a breakpoint in gdb. What I meant was
>>> put printf's in your code and run the program and look at the
>>> output. You can use fprintf's to stderr if your prefer and just
>>> look at the stderr output.
>>>
>>> It is hard to diagnose what could be a compiler error, or a coding
>>> error. Remember in C you can do many things you really shouldn't.
>>> It is also advisable to run lint over your source code too.
>>
>> All that lint shows is it doesn't like comments using // and lots of
>> errors in /usr/include files.
>
> This sounds more like a c++ program. c++ does a lot of variable
> initiation in code you usually won't see.
>
> If this is a c++ program, put conditional printf's or cout's in to
> check the code at actual runtime rather than in the debugger.
>
> You may want to use asserts.
Nope. Very simple c code. I believe as was pointed out earlier that
this is a gdb issue. Once gdb found the right value, both it and all
the printfs show the correct value. I changed nothing. I am a bit
concerned since this is now in a production system that it may
eventually start fail again which would have some serious consequences.
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