C#截取字符串长度方法

/// <summary>
/// 截取指定长度的字符串
/// </summary>
/// <param name="str">要截取的字符串</param>
/// <param name="len">要截取的长度</param>
/// <param name="flag">截取后是否加省略号(true加,false不加)</param>
/// <returns></returns>
public static string CutString(string str, int len, bool flag)
{
string _outString = "";
int _len = 0;
for (int i = 0; i < str.Length; i++)
{
if (Char.ConvertToUtf32(str, i) >= Convert.ToInt32("4e00", 16) && Char.ConvertToUtf32(str, i) <= Convert.ToInt32("9fff", 16))
{
_len += 2;
if (_len > len)//截取的长度若是最后一个占两个字节，则不截取
{
break;
}
}
else
{
_len++;
}

try
{
_outString += str.Substring(i, 1);
}
catch
{
break;
}
if (_len >= len)
{
break;
}
}
if (str != _outString && flag == true)//判断是否添加省略号
{
_outString += "...";
}
return _outString;
}

/// <summary>
/// 截取指定长度的字符串
/// </summary>
/// <param name="str">要截取的字符串</param>
/// <param name="len">要截取的长度</param>
/// <param name="flag">截取后是否加省略号(true加,false不加)</param>
/// <returns></returns>
public static string CutString(string str, int len, bool flag)
{
System.Text.ASCIIEncoding ascii = new System.Text.ASCIIEncoding();
byte[] bts = ascii.GetBytes(str);
int _len = 0;
string _outString = "";
for (int i = 0; i < bts.Length; i++)
{
if ((int)bts[i] == 63)//两个字符
{
len += 2;
if (_len > len)//截取的长度若是最后一个占两个字节，则不截取
{
break;
}
}
else
{
len += 1;
}

try
{
_outString += str.Substring(i, 1);
}
catch
{
break;
}

if (_len >= len)
{
break;
}
}
if (str != _outString && flag == true)//判断是否添加省略号
{
_outString += "...";
}
return _outString;
}

/// <summary>
/// 截取指定长度的字符串
/// </summary>
/// <param name="str">要截取的字符串</param>
/// <param name="len">要截取的长度</param>
/// <param name="flag">截取后是否加省略号(true加,false不加)</param>
/// <returns></returns>
public static string CutString(string str, int len, bool flag)
{
if (str == null || str.Length == 0 || len <= 0)
{
return string.Empty;
}

int l = str.Length;

#region 计算长度
int clen = 0;
while (clen < len && clen < l)
{
//每遇到一个中文，则将目标长度减一。
if ((int)str[clen] > 128)
{
len--;
}
clen++;
}
#endregion

if (clen < l)
{
return flag ? str.Substring(0, clen) + "..." : str.Substring(0, clen);
}
else
{
return str;
}
}