如何使用 c# 替换字符串的最后一个字符？

Question

string str = "Student_123_";

I need to replace the last character "_" with ",". I did it like this.

str.Remove(str.Length -1, 1);
str = str + ",";

However, is it possible to achieve it more efficiently. may be one line of code.?? BTW, last character can be any character. So Replace wont work here.

Answer 1

No.

In C# strings are immutable and thus you can not change the string "in-place". You must first remove a part of the string and then create a new string. In fact, this is also means your original code is wrong, since str.Remove(str.Length -1, 1); doesn't change str at all, it returns a new string: This should do:

str = str.Remove(str.Length -1, 1) + ",";

Answer 2

C# .NET makes it almost too easy.

str = str.TrimEnd('_')

Answer 3

That's a limitation of working with string . You can use StringBuilder if you need to do a lot of changes like this. But it's not worth it for the simple task you need.

str = str.Substring(0, str.Length - 1) + ",";

Answer 4

Elegant but not very efficient. Replaces any character at the end of str with a comma.

str = Regex.Replace(str, ".$", ",");

Answer 5

Use the StringBuilder class

StringBuilder mbuilder = new StringBuilder("Student_123_");
mbuilder[mbuilder.Length-1] = ',';
Console.WriteLine(mbuilder.ToString());

Answer 6

str = str.Substring(0, str.Length-1) + ",";

Answer 7

Well, what you have won't work because str.Remove(...) doesn't manipulate str , it returns a new string with the removal operation completed on it.

So - you need:

str = str.Remove(str.Length-1,1);
str = str + ",";

In terms of efficiency, there are several other choices you could make (substring, trim...) but ultimately you're going to get the same time/space complexity.

EDIT:

Also, don't try to squash everything into one line, the programmers who come after you will appreciate the greater readability. (Although in this case a single line is just as easy to read.) One line.= more efficient.

Answer 8

With one line of code you could write:

str = str.Remove(str.Length - 1, 1) + ",";

Answer 9

str.Remove doesn't modify str , it returns a new string. Your first line should read str = str.Remove...

One line? OK: str = str.Remove(str.Length - 1) + ",";

I think that's as efficient as you're going to get. Technically, you are creating two new strings here, not one (The result of the Remove, and the result of the Concatenation). However, everything I can think of to not create two strings, ends up creating more than 1 other object to do so. You could use a StringBuilder, but that's heavier weight than an extra string, or perhaps a char[] , but it's still an extra object, no better than what I have listed above.