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6017 :: how to deal with C string with \0?

• oyster (orginal) [2020-03-02T04:50:03+01:00] view original

  As https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getlogicaldrivestringsw said, the sting in returned lpBuffer is

  
  C:\\\0D:\\\0
  Run

  then we can spilt at \0 to tell the real name of logical driver

  Then I translate the code into nim

  import winim
  proc GetLogicalDriveStringsW(nBufferLength: DWORD; lpBuffer: LPTSTR): DWORD {.stdcall, dynlib: "kernel32", importc, discardable.}
  
  
  var szAllDriveStrings = GetLogicalDriveStringsW(0, NULL)
  
  echo szAllDriveStrings
  
  if szAllDriveStrings > 0:
      var lpDriveStrings:LPTSTR = cast[LPTSTR](HeapAlloc(GetProcessHeap(), 0, cast[SIZE_T](szAllDriveStrings*sizeof(TCHAR))))
      GetLogicalDriveStringsW(szAllDriveStrings, lpDriveStrings)
      echo lpDriveStrings  # only C:\
      
      var x = newString(szAllDriveStrings*sizeof(TCHAR))
      copyMem(addr(x[0]), lpDriveStrings, szAllDriveStrings*sizeof(TCHAR))
      echo x  # C:\D:\
  Run

  so what is the proper way to deal with C's LPTSTR, how can I get C:`, `D:`? No I don't think I sould split the string at `` then attach `` to `C: and D:?

  to be more common, what if there are more \0 in a C string, how can we deal the information correctly in nim?

  thanks

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• leorize (orginal) [2020-03-02T07:44:03+01:00] view original

  Here you go:

  https://play.nim-lang.org/#ix=2d96

  As I don't use Windows, I can't verify the code and have only written it based on documentations lying around.

  Please note that the string that GetLogicalDriveStringsW returns is a wide string, not a C string, and along with it's other API quirks, I'd say that correctly getting a buffer was not as easy as I imagined.

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• leorize (orginal) [2020-03-02T08:10:38+01:00] view original

  to be more common, what if there are many 0 in a C string, how can we deal the information correctly in nim?

  Hope this helps: https://play.nim-lang.org/#ix=2d9d

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• JohnS (orginal) [2020-03-03T04:10:25+01:00] view original

  psutil has this function in case you'd rather use that (or see how we did it).

  import psutil
  echo disk_partitions()
  Run

  produces:

  
  @[(device: "C:\\", mountpoint: "C:\\", fstype: "NTFS", opts: "rw,fixed"), (device: "D:\\", mountpoint: "D:\\", fstype: "NTFS", opts: "rw,fixed")]
  Run

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• Ward (orginal) [2020-03-03T13:30:28+01:00] view original

  You can try running this code with different mode:

  import winim/lean, strutils
  
  var bufLen = GetLogicalDriveStrings(0, nil)
  var buffer = T(bufLen)
  
  GetLogicalDriveStrings(bufLen, buffer)
  echo buffer
  echo buffer.repr
  echo ($buffer).repr
  echo cstring($buffer)
  echo ($buffer).split('\0')
  
  Run

  
  nim c -r test.nim
  nim c -r -d:useWinAnsi test.nim
  Run

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