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4326 :: How does one convert from string to integer using an arbitrary radix?

• vsajip (orginal) [2018-10-21T00:01:21+02:00] view original

  I see the parseutils module has parseHex, parseOct and parseInt and the dom module exposes a C function parseInt that converts a C string to a number with an arbitrary radix, but I don't see a parseInt(s: string, radix: int): int in the documentation. Have I missed it, or is this functionality itself missing? Searching in the documentation on radix and base didn't throw up anything. Example use case: parsing a C-like integer constant - if it starts with '0', parse with radix 8, else with radix 10.

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• DeletedUser (orginal) [2018-10-21T17:53:52+02:00] view original

  Not in the standard library. Example implementation here https://rosettacode.org/wiki/Non-decimal_radices/Convert#Nim

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• vsajip (orginal) [2018-10-21T23:00:16+02:00] view original

  Thanks for the pointer. I adapted the example like this:

  
  const DIGITS = "0123456789"
  
  proc parseInt(s : string, radix: range[8..10]) : uint64 =
    var str = s
    result = 0
    
    for i in 0 .. str.high:
      let c = str[i]
      assert c in DIGITS[0 ..< radix]
      result = result * radix + uint64(DIGITS.find c)
  
  echo parseInt("077", 8)
  Run

  It compiles, and seems to run as expected, but I get a warning which is hard to understand:

  
  Hint: used config file '/nim/config/nim.cfg' [Conf]
  Hint: system [Processing]
  Hint: in [Processing]
  in.nim(9, 14) template/generic instantiation from here
  lib/system.nim(325, 3) Warning: Cannot prove that 'result' is initialized. This will become a compile time error in the future. [ProveInit]
  Run

  It's complaining about the assert line - but I can't see the connection between that and result, and moreover result is initialized at line 5, result = 0. Any ideas how to interpret this?

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• lscrd (orginal) [2018-10-21T23:39:22+02:00] view original

  The message is misleading. "result" is the one at line 325 in system.nim, i.e. the HSlice which is returned by the proc.

  When instanciating the slice (".."), the fields "a" and "b" of "result" (a slice) should be initialized with 0. But "b" is of type "range[8..10] and cannot be initialized with this value. So, the compiler emits a warning.

  To avoid this warning, you simply can write "assert c in DIGITS[0 ..< radix.int]".

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• vsajip (orginal) [2018-10-22T06:45:57+02:00] view original

  Great, thanks.

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• mratsim (orginal) [2018-10-22T11:08:21+02:00] view original

  You can use this bigint implementation as reference: https://github.com/status-im/nim-stint/blob/4fe901d33b9f5b3ad5f51a587bf6bbb6eb20121b/stint/io.nim#L135-L154

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