C#截取指定字节长度的中英文混合字符串

using System.Text.RegularExpressions;
using System.Text;

/// 

/// 字符串长度(按字节算)
/// 
/// 
/// 
static int StrLength(string str)
{
    int len = 0;
    byte[] b;

    for (int i = 0; i < str.Length; i++)
    {
        b = Encoding.Default.GetBytes(str.Substring(i,1));
        if (b.Length > 1)
            len += 2;
        else
            len++;
    }

    return len;
}

/// 

/// 截取指定长度字符串(按字节算)
/// 
/// 
/// 
/// 
static string StrCut(string str, int length)
{
    int len = 0;
    byte[] b;
    StringBuilder sb = new StringBuilder();

    for (int i = 0; i < str.Length; i++)
    {
        b = Encoding.Default.GetBytes(str.Substring(i, 1));
        if (b.Length > 1)
            len += 2;
        else
            len++;

        if (len >= length)
            break;

        sb.Append(str[i]);
    }

    return sb.ToString();
}