C# Changing a string after it has been created

Question

Okay I know this question is painfully simple, and I'll admit that I am pretty new to C# as well. But the title doesn't describe the entire situation here so hear me out.

I need to alter a URL string which is being created in a C# code behind, removing the substring ".aspx" from the end of the string. So basically I know that my URL, coming into this class, will be something like "Blah.aspx" and I want to get rid of the ".aspx" part of that string. I assume this is quite easy to do by just finding that substring, and removing it if it exists (or some similar strategy, would appreciate if someone has an elegant solution for it if they've thought done it before). Here is the problem:

"Because strings are immutable, it is not possible (without using unsafe code) to modify the value of a string object after it has been created." This is from the MSDN official website. So I'm wondering now, if strings are truly immutable, then I simply can't (shouldn't) alter the string after it has been made. So how can I make sure that what I'm planning to do is safe?

Answer 1

You don't change the string, you change the variable. Instead of that variable referring to a string such as "foo.aspx", alter it to point to a new string that has the value "foo".

As an analogy, adding one to the number two doesn't change the number two. Two is still just the same as it always way, you have changed a variable from referring to one number to refer to another.

As for your specific case, EndsWith and Remove make it easy enough:

if (url.EndsWith(".aspx"))
    url = url.Remove(url.Length - ".aspx".Length);

Note here that Remove is taking one string, an integer, and giving us a brand new string, which we need to assign back to our variable. It doesn't change the string itself.

Also note that there is a URI class that you can use for parsing URLs, and it will be able to handle all of the complex situations that can arise, including hashes, query parameters, etc. You should use that to parse out the aspects of a URL that you are interested in.