C# 取一个字符串的子串 [英] C# take a substring of a string

问题描述

仅当该文件没有特定模式时，我才从文件中取出一行..我想从该行中取出最后 3 个字符...我的代码是:

I am taking a line from a file only if that file doen't have a specific pattern.. and i want to take from that line the last 3 chars... my code is:

        while (!line.Contains(pattern))
        {
             String num = line.Substring((line.Length - 3), (line.Length - 2));
             System.Console.WriteLine(num);
        }

但是我得到一个错误..

but i get an error..

索引和长度必须指向字符串中的某个位置.参数名称:长度

Index and length must refer to a location within the string. Parameter name: length

为什么我会这样?我在行尾前 3 个字符开始新字符串，然后在 .. 之前停止 2 个字符:\

why i get that? i am starting the new string 3 chars before the end of the line and i stop 2 chars before.. :\

推荐答案

Substring 接受一个偏移量，然后返回一些字符:

Substring takes an offset and then a number of characters to return:

http://msdn.microsoft.com/en-us/library/aa904308%28v=VS.71%29.aspx

所以:

String num = line.Substring((line.Length - 3), 3);

这当然假设 line.Length > 3.你可以检查:

This of course assumes that line.Length > 3. You could check with:

String num = (line.Length < 3) ? line : line.Substring((line.Length - 3), 3);

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