c# 判断字符是否是全角, 获取字符串的字节数 , 获取字符串指定长度字节数的字符串

/// <summary>
/// 获取字符串的字节长度
/// </summary>
/// <param name="str"></param>
/// <returns></returns>
public static int GetStringByteLength(this string str)
{
int j = 0;
foreach (char c in str)
{
string checkString = c + "";
j += Encoding.Default.GetByteCount(checkString);
}
return j;
}

/// <summary>
/// 根据字节数截取字符串
/// </summary>
/// <param name="s">输入的字符串</param>
/// <param name="length">要截取的字节长度</param>
/// <returns></returns>
public static string bSubstring(this string s, int length)
{
if (length>=s.GetStringByteLength())
{
return s;
}
string outStr="";
int j = 0;
foreach (char c in s)
{
string checkString = c + "";
j += Encoding.Default.GetByteCount(checkString);
outStr += c;
if (j>=length) break;
}
return outStr;
}