KOZの館 - Visual Basic Programming -

サロゲートペアを１文字として認識するよう、LenB, LeftB, MidB, RightB の例にならい、LenU, LeftU, MidU, RightU を実装します。

 #region サロゲートペアを意識した文字列操作関数
 
 public static int LenU(string str)
 {
     if (string.IsNullOrEmpty(str)) return 0;
 
     int lengthC = str.Length;
     int lengthU = 0;
     int i = 0;
     while (i < lengthC)
     {
         char c = str[i];
         if (i + 1 < lengthC && char.IsSurrogatePair(c, str[i + 1]))
         {
             lengthU++;
             i += 2;
         }
         else
         {
             lengthU++;
             i += 1;
         }
     }
     return lengthU;
 }
 
 public static string LeftU(string str, int length)
 {
     return MidU(str, 1, length);
 }
 
 public static string MidU(string str, int start)
 {
     int length = LenU(str) - start + 1;
     return MidU(str, start, length);
 }
 
 public static string MidU(string str, int start, int length)
 {
     if (string.IsNullOrEmpty(str)) return string.Empty;
 
     // 開始位置を検索
 
     int lengthC = str.Length;
     int skipLength = 0;
     int pos = 0;
     start = start - 1;
     while (pos < lengthC && skipLength < start)
     {
         char c = str[pos];
         if (pos + 1 < lengthC && char.IsSurrogatePair(c, str[pos + 1]))
         {
             skipLength++;
             pos += 2;
         }
         else
         {
             skipLength++;
             pos += 1;
         }
     }
 
     // 開始位置以降の文字を取得
 
     StringBuilder builder = new StringBuilder();
     int lengthU = 0;
 
     while (pos < lengthC && lengthU < length)
     {
         char c = str[pos];
         if (pos + 1 < lengthC && char.IsSurrogatePair(c, str[pos + 1]))
         {
             builder.Append(c);
             builder.Append(str[pos + 1]);
             lengthU++;
             pos += 2;
         }
         else
         {
             builder.Append(c);
             lengthU++;
             pos += 1;
         }
     }
     return builder.ToString();
 }
 
 public static string RightU(string str, int length)
 {
     if (length <= 0) return string.Empty;
     int lengthU = LenU(str);
     if (length > lengthU) length = lengthU;
 
     int pos = lengthU - length + 1;
     return MidU(str, pos, length);
 }
 
 #endregion

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