Date: Sat, 15 Mar 2008 07:59:57 -0500 From: Derek Ragona <derek@computinginnovations.com> To: Doug Hardie <bc979@lafn.org> Cc: freebsd-questions <freebsd-questions@freebsd.org> Subject: Re: C compiler issue perhaps? Message-ID: <6.0.0.22.2.20080315075146.02610a20@mail.computinginnovations.com> In-Reply-To: <EE488DB7-2E54-48F5-A3E2-1357BF848978@lafn.org> 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>
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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.
-Derek
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