/// <summary>
/// 截断字符串，如果str 的长度超过 need，则提取 str 的前 need 个字符，并在尾部加 “...”
/// </summary>
public static string Left(string s, int need, bool encode)
{
if (s == null || s == "")
{
return(string.Empty);
}
int len = s.Length;
// int len = NumChar(s);
if (len < need / 2)
{
return(encode ? TextEncode(s) : s);
}
int i, j, bytes = 0;
for (i = 0; i < len; i++)
{
bytes += RegExp.IsUnicode(s[i].ToString()) ? 2 : 1;
if (bytes >= need)
{
break;
}
}
string result = s.Substring(0, i);
if (len > i)
{
for (j = 0; j < 5; j++)
{
bytes -= RegExp.IsUnicode(s[i - j].ToString()) ? 2 : 1;
if (bytes <= need)
{
break;
}
}
result = s.Substring(0, i - j) + "...";
}
return(encode ? TextEncode(result) : result);
}
