C# replace string in string

Is it possible to replace a substring in a string without assigning a return value?

I have a string:

string test = "Hello [REPLACE] world";

And I want to replace the substring [REPLACE] with something else:

test = test.replace("[REPLACE]", "test");

This works fine, but how can I do it without assigning the return value to a variable?

I want something like this:

test.replace(开发者_如何学编程"[REPLACE]", "test");

---

As mentioned by dlev, you can't do this with string as strings are immutable in .NET - once a string has been constructed, there's nothing you can do (excluding unsafe code or reflection) to change the contents. This makes strings generally easier to work with, as you don't need to worry about defensive copying, they're naturally thread-safe etc.

Its mutable cousin, however, is StringBuilder - which has a Replace method to perform an in-object replacement. For example:

string x = "Hello [first] [second] world";

StringBuilder builder = new StringBuilder(x);
builder.Replace("[first]", "1st");
builder.Replace("[second]", "2nd");

string y = builder.ToString(); // Value of y is "Hello 1st 2nd world"

---

You can't, because string is immutable. It was designed so that any "changes" to a string would actually result in the creation of a new string object. As such, if you don't assign the return value (which is the "updated" string, actually copy of the original string with applied changes), you have effectively discarded the changes you wanted to make.

If you wanted to make in-place changes, you could in theory work directly with a char[] (array of characters), but that is dangerous, and should be avoided.

Another option (as pointed out by Mr. Skeet below) is to use StringBuilder and its Replace() method. That being said, simple replacements like the one you've shown are quite fast, so you may not want to bother with a StringBuilder unless you'll be doing so quite often.

---

Strings in .NET are immutable. They cannot be edited in-line.

The closest you can get to in-line editing is to create a StringBuilder from a string. In-line fiddles with its contents and then get it to spit a string back out again.

But this will still produce a new string rather than altering the original. It is a useful technique, though, to avoid generating lots of intermediary strings when doing lots of string fiddling, e.g. in a loop.

---

You can't. You have to assign the value, as strings are immutable.

Built-in reference types (C# reference)

---

You can't. Strings are immutable in .NET.

---

You can't, as in C# strings are immutable. Something like this would violate that.

You need to have the return type of string, because the one you're working with cannot change.

---

Here is the code to fetch a string from HTML content and pass it to StringBuilder and set the value from your variable. You cannot do string.replace. You have to use StringBuilder while manipulating. Here in the HTML page I added [Name] which is replaced by Name from code behind. Make sure [Name] is unique or you can give any unique name.

string Name = txtname.Text;
string contents = File.ReadAllText(Server.MapPath("~/Admin/invoice.html"));

StringBuilder builder = new StringBuilder(contents);

builder.Replace("[Name]", Name);

StringReader sr = new StringReader(builder.ToString());