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2761 :: [newbie question] Pointer to cstring

• mmierzwa (orginal) [2017-01-26T21:43:20+01:00] view original

  Hi

  I am having hard time understanding pointers, addr, cstrings.

  var i: cstring = "a"
  var pi: ptr cstring = i.addr
  echo repr(i)
  echo repr(pi)
  Run

  Output:

  
  005BC058"a"
  ref 004477F8 --> 005BC070"a"
  Run

  My understanding is this. First we declare variable i and assign string "a" there. As first line of output says, "a" is kept in ...058 cell of memory so in fact i contains address of this cell. Now we are declaring pointer pi and assign address of i. Is it that pi points to i that points to ...058 memory which contains "a"? As I understand from second ouput line address of pi variable is ...77F8, but then it is suggesting that "a" is in memory cell C070. I am a bit confused. Could you help me understand?

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• Krux02 (orginal) [2017-01-26T23:46:27+01:00] view original

  In my opinion your understanding is right. I think there is just something weird happening with cstring.

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• Araq (orginal) [2017-01-26T23:51:27+01:00] view original

  repr is a zombie. Don't use it for anything. I fixed it anyway.

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• mmierzwa (orginal) [2017-01-27T08:28:14+01:00] view original

  Thank you Krux and Araq. repr is very useful to be able to understand what is going on in my program. I am trying to send strings through a pipe (without success) so casting to pointer and knowing what is exactly happening is crucial for me.

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• Araq (orginal) [2017-01-27T12:20:49+01:00] view original

  echo cast[int](mypointer) doesn't require repr.

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• dom96 (orginal) [2017-01-27T12:30:23+01:00] view original

  repr is a zombie.

  What does that mean?

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• Krux02 (orginal) [2017-01-27T17:05:27+01:00] view original

  Maybe he wants to depricate it. I mean it is also not really defined what it does. From the description it is not much different than $. And there are issues with it like this one: https://github.com/nim-lang/Nim/issues/5268

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• Araq (orginal) [2017-01-27T17:21:01+01:00] view original

  It seems to be too popular to deprecate and remove...

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• Krux02 (orginal) [2017-01-27T17:40:59+01:00] view original

  But you can change the description to something less appealing: Instead of "This is a great debugging tool" it could be "it can be used for debugging, but the output format is not something any program should rely on". Maybe then it becomes less popular. And then what is the alternative? I don't even know what your exact problems with repr is. I use it basically only for macro debugging, because it is almost the reverse of the parser. Not 100% though, but good enough to use it for debugging.

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