Modified UTF-7のエンコード・デコード - smdn.jp

public static string ToModifiedUTF7String(string str) { var encoded = new StringBuilder(); var shiftFrom = -1; for (var index = 0; index < str.Length; index++) { var c = str[index]; if ((0x20 <= c && c <= 0x7e)) { if (0 <= shiftFrom) { // string -> modified UTF7 encoded.Append('&'); encoded.Append(ToModifiedUTF7(str.Substring(shiftFrom, index - shiftFrom))); encoded.Append('-'); shiftFrom = -1; }