C#写的读取ISO2709格式数据的DLL[2]

  // 通过字段名，字段中出现次数获得字段内容
  // 次数从 1  开始计数
  // -1 error
  // 0  no found
  // 1  found
  public int GetField(string strFldName,
   int nIndex,
   out string strFld)
  {
   strFld = null;
   
   string strFldPos = null;
   int nRet = this.GetFieldPos(strFldName,nIndex,out strFldPos);
   if (nRet != 1)
    return nRet;
   if(strFldName.Length != 3 )
    return -1;  // subfield must 3 chars
   
   int nLength = int.Parse( strFldPos.Substring(3,4));
   int nBeginPos = int.Parse( strFldPos.Substring(7,5));
   char[] chData = this.GetData().ToCharArray();
   int nPos =0;
   int i = 0;
   while( nPos < chData.Length)
   {
    i += GetCharLength(chData[nPos]);
    if((i >= nBeginPos) && i<= (nBeginPos + nLength))
     strFld += chData[nPos].ToString();
    nPos ++;

   }
   if(strFld == null)
    return 0;
   return 1;
  }
  //从字段中获得出现次数的子字段
  // -1 error
  // 0 not found
  // 1 found
  public int GetSubField(string strFld,
   string  strSubName,
   int nIndex,
   out string strSubFld)
  {
   strSubFld  = null;
   if(strSubName.Length != 1)
    return -1; // subfield'symbol char must 1 char
   if(strFld == null)
    return -1;
   
   char[] chData = strFld.ToCharArray();
   int nPos = 0;
   bool isNewSub = false;
   int nFound = 0; // 0: not 1: first time found 2: second time found
   while( nPos < chData.Length)
   {    
    nPos ++; 
 
    if((chData[nPos-1] == SUBFLD) && (chData[nPos].ToString() == strSubName))
     nFound ++; // found    

    if ((nFound == nIndex) && (isNewSub == false))
    {     
     if(chData[nPos] == SUBFLD)
     {
      isNewSub = true;
      break;
     }
     strSubFld += chData[nPos].ToString();
    }

   }
   if(strSubFld == null)
    return 0;
   return 1;
  }

  //从字段组中获得子字段
  // -1 error
  // 0 not found
  // 1 found
  public int GetSubField(string strGroup,
   string  strSubName,
   out string strSubFld)
  {
   strSubFld  = null;
   if(strSubName.Length != 1)
    return -1; // subfield'symbol char must 1 char
   if(strGroup == null)
    return -1;
   
   char[] chData = strGroup.ToCharArray();
   int nPos = 0;
   bool isNewSub = false;
   int nFound = 0; // 0: not 1: first time found 2: second time found
   while( nPos < chData.Length)
   {    
    nPos ++; 
 
    if((chData[nPos-1] == SUBFLD) && (chData[nPos].ToString() == strSubName))
     nFound ++; // found    

    if (isNewSub == false)
    {     
     if(chData[nPos] == SUBFLD)
     {
      isNewSub = true;
      break;
     }
     strSubFld += chData[nPos].ToString();
    }