C compiler issue perhaps?

[Derek Ragona]

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.

         -Derek

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