string mystring = "34234234d124";
mystring = mystring.Substring(mystring.Length-4)

假设你想要一个距离最后一个字符10个字符的字符串之间的字符串，你只需要3个字符。

我们写入StreamSelected = "rtsp://72.142.0.230:80/ smile - chan -273/ 4cif -273.stream"

在上面，我需要提取我将在数据库查询中使用的“273”

        //find the length of the string            
        int streamLen=StreamSelected.Length;

        //now remove all characters except the last 10 characters
        string streamLessTen = StreamSelected.Remove(0,(streamLen - 10));   

        //extract the 3 characters using substring starting from index 0
        //show Result is a TextBox (txtStreamSubs) with 
        txtStreamSubs.Text = streamLessTen.Substring(0, 3);

你可以使用扩展方法:

public static class StringExtension
{
    public static string GetLast(this string source, int tail_length)
    {
       if(tail_length >= source.Length)
          return source;
       return source.Substring(source.Length - tail_length);
    }
}

然后调用:

string mystring = "34234234d124";
string res = mystring.GetLast(4);

string var = "12345678";

if (var.Length >= 4)
{
    var = var.substring(var.Length - 4, 4)
}

// result = "5678"

这工作得很好，因为如果字符串中的字符比请求的数量少，也不会出现错误。

using System.Linq;

string.Concat("123".TakeLast(4));

mystring = mystring.Length > 4 ? mystring.Substring(mystring.Length - 4, 4) : mystring;