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267 :: Segfault in loop

• achesak (orginal) [2013-10-08T02:19:53+02:00] view original

  As a bit of background for the problem, I'm trying to loop through a list of PXmlNodes and extract the info from them.

  The code that is having the problem:

  
  echo(len(xml.findAll("item")))
  for i in 0..high(xml.findAll("item")):
      echo(i)
      watches[i] = parseRSS(xml.findAll("item")[i])
      echo(i)
  Run

  watches is an array, and parseRSS is a function for getting information out of the XML and returning it as a custom type.

  When the program is run, the following is output:

  
  5
  0
  0
  1
  1
  2
  2
  3
  3
  4
  Segmentation fault (core dumped)
  Run

  So it runs up to the fifth item, but then segfaults.

  What's causing this, and how would I change the code to avoid this?

  Thanks in advance for any help.

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• Araq (orginal) [2013-10-08T11:57:49+02:00] view original

  In debug mode you should get a stack trace unless you have a stack overflow.

  Please make proper bug reports with code that we can run ourselves.

  Maybe you run with -d:release and the array has only space for 4 items? ;-)

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• achesak (orginal) [2013-10-08T15:15:15+02:00] view original

  Sorry, when I wrote that I was tired, I'll try to do better. :p

  The array has enough space, I made sure to check that.

  Here's the full code: http://pastebin.com/dMC88txS

  Note that the output is slightly different now, but it's the same problem:

  
  4
  0
  0
  1
  1
  2
  2
  3
  3
  Segmentation fault (core dumped)
  Run

  This isn't due to changes I made in the program, but rather with changes in the data.

  As for the stack trace, I'm afraid that I have really no experience with debuggers and no idea what to do. I'll go off and RTFM and edit later if I can figure it out. :p

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• Araq (orginal) [2013-10-08T18:25:16+02:00] view original

  You don't have to do anything to get a stack trace. However in your case you corrupted the stack so no stack trace works.

  The problem is that due to a regression the compiler currently doesn't complain about the array with dynamic bounds that you use; arrays with dynamic bounds are not supported at all and your code shouldn't compile. You need to use a seq instead and either add to it or initialize it via var s = newSeq[YourType](YourSize). Then your program shouldn't crash anymore.

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• achesak (orginal) [2013-10-08T19:06:14+02:00] view original

  Thanks so much (again)! I'm mostly used to working with dynamic languages where this sort of thing never happens (like Python), so it's taking me a bit of time to get used to it.

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