按字节长度截取字符串，支持截取带HTML代码样式的字符串
/// <summary>
/// 按字节长度截取字符串(支持截取带HTML代码样式的字符串)
/// </summary>
/// <param name="param">将要截取的字符串参数</param>
/// <param name="length">截取的字节长度</param>
/// <param name="end">字符串末尾补上的字符串</param>
/// <returns>返回截取后的字符串</returns>
public string SubstringToHTML(string param, int length, string end)
{
string Pattern = null;
MatchCollection m = null;
StringBuilder result = new StringBuilder();
int n = 0;
char temp;
bool isCode = false; //是不是HTML代码
bool isHTML = false; //是不是HTML特殊字符,如
char[] pchar = param.ToCharArray();
for (int i = 0; i < pchar.Length; i++)
{
temp = pchar[i];
if (temp == '<')
{
isCode = true;
}
else if (temp == '&')
{
isHTML = true;
}
else if (temp == '>' && isCode)
{
n = n - 1;
isCode = false;
}
else if (temp == ';' && isHTML)
{
isHTML = false;
}
if (!isCode && !isHTML)
{
n = n + 1;
//UNICODE码字符占两个字节
if (System.Text.Encoding.Default.GetBytes(temp + "").Length > 1)
{
n = n + 1;
}
}
result.Append(temp);
if (n >= length)
{
break;
}
}
result.Append(end);
//取出截取字符串中的HTML标记
string temp_result = result.ToString().Replace("(>)[^<>]*(<?)", "$1$2");
//去掉不需要结素标记的HTML标记
temp_result = temp_result.Replace(@"</?(AREA|BASE|BASEFONT|BODY|BR|COL|COLGROUP|DD|DT|FRAME|HEAD|HR|HTML|IMG|INPUT|ISINDEX|LI|LINK|META|OPTION|P|PARAM|TBODY|TD|TFOOT|TH|THEAD|TR|area|base|basefont|body|br|col|colgroup|dd|dt|frame|head|hr|html|img|input|isindex|li|link|meta|option|p|param|tbody|td|tfoot|th|thead|tr)[^<>]*/?>",
"");
//去掉成对的HTML标记
temp_result = temp_result.Replace(@"<([a-zA-Z]+)[^<>]*>(.*?)</\1>", "$2");
//用正则表达式取出标记
Pattern = ("<([a-zA-Z]+)[^<>]*>");
m = Regex.Matches(temp_result, Pattern);
ArrayList endHTML = new ArrayList();
foreach (Match mt in m)
{
endHTML.Add(mt.Result("$1"));
}
//补全不成对的HTML标记
for (int i = endHTML.Count - 1; i >= 0; i--)
{
result.Append("</");
result.Append(endHTML[i]);
result.Append(">");
}
return result.ToString();
}