Replace "\\" with "\" in a string in C#

Question

I still don't get how to do this. I saw many posts regarding this, but none of the solutions worked for me.

I have a string called "a\\b". The result I need is "a\b". How is this done?

I have a text file which has a database connection string pointing to an instance called - Server\DbInstance

My aim is to do a string replace in the text file -- replace "Server\DbInstance" with another value, say "10.11.12.13, 1200".

So I have:

stringToBeReplaced = @"Server\DbInstance";
newString = @"10.11.12.13, 1200";

This is where the problem starts. My stringToBeReplaced will always be "Server\\DbInstance", and when I search for this string in my text file, the search fails, as the text file doesn't have a string "Server\\DbInstance"; instead it has only "Server\DbInstance". So how do change "Server\\DbInstance" to "Server\DbInstance"?

Solution 1

I suspect your string already actually only contains a single backslash, but you're looking at it in the debugger which is escaping it for you into a form which would be valid as a regular string literal in C#.

If print it out in the console, or in a message box, does it show with two backslashes or one?

If you actually want to replace a double backslash with a single one, it's easy to do so:

text = text.Replace(@"\\", @"\");

... but my guess is that the original doesn't contain a double backslash anyway. If this doesn't help, please give more details.

EDIT: In response to the edited question, your stringToBeReplaced only has a single backslash in. Really. Wherever you're seeing two backslashes, that viewer is escaping it. The string itself doesn't have two backslashes. Examine stringToBeReplaced.Length and count the characters.

Solution 2

in case someone got stuck with this and none of the answers above worked, below is what worked for me. Hope it helps.

var oldString = "\\r|\\n";

// None of these worked for me
// var newString = oldString(@"\\", @"\");
// var newString = oldString.Replace("\\\\", "\\");
// var newString = oldString.Replace("\\u5b89", "\u5b89");
// var newString = Regex.Replace(oldString , @"\\", @"\");

// This is what worked
var newString = Regex.Unescape(oldString);
// newString is now "\r|\n"

Solution 3

I tried the procedures of your posts but with no success.

This is what I get from debugger:

Original string that I save into sqlite database was b\r\na .. when I read them, I get b\\r\\na (length in debugger is 6: "b" "\" "\r" "\" "\n" "a") then I try replace this string and I get string with length 6 again (you can see in picture above).

I run this short script in my test form with only one text box:

private void Form_Load(object sender, EventArgs e)
    {
        string x = "b\\r\\na";
        string y = x.Replace(@"\\", @"\");
        this.textBox.Text = y + "\r\n\r\nLength: " + y.Length.ToString();
    }

and I get this in text box (so, no new line characters between "b" and "a":

b\r\na

Length: 6

What can I do with this string to unescape backslash? (I expect new line between "b" and "a".)

Solution:

OK, this is not possible to do with standard replace, because of \r and \n is one character. Is possible to replace part of string character by character but not possible to replace "half part" of one character. So, I must replace any special character separatelly, like this:

private void Form_Load(object sender, EventArgs e) {
    ...
    string z = x.Replace(@"\r\n", Environment.NewLine);
    ...

This produce correct result for me:

b
a

Solution 4

I was having the same problem until I read Jon Skeet's answer about the debugger displaying a single backslash with a double backslash even though the string may have a single backslash. I was not aware of that. So I changed my code from

text2 = text1.Replace(@"\\", @"/");

to

text2 = text1.Replace(@"\", @"/");

and that solved the problem. Note: I'm interfacing and R.Net which uses single forward slashes in path strings.

Solution 5

Regex.Unescape(string) method converts any escaped characters in the input string.

The Unescape method performs one of the following two transformations:

1. It reverses the transformation performed by the Escape method by removing the escape character ("\") from each character escaped by the method. These include the \, *, +, ?, |, {, [, (,), ^, $, ., #, and white space characters. In addition, the Unescape method unescapes the closing bracket (]) and closing brace (}) characters.

2. It replaces the hexadecimal values in verbatim string literals with the actual printable characters. For example, it replaces @"\x07" with "\a", or @"\x0A" with "\n". It converts to supported escape characters such as \a, \b, \e, \n, \r, \f, \t, \v, and alphanumeric characters.

string str = @"a\\b\\c";
var output = System.Text.RegularExpressions.Regex.Unescape(str);

Reference:

https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.regex.unescape?view=netframework-4.8

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Comments

[Olle89]

do you need a string that has the value "a\b" or writes "a\b" when its printed?

[Sandeep]

Its still not working for me :( I have updated the question with my current scenario.

[Jon Skeet]

@user762730: The string you have shown only has a single backslash in. You haven't been clear about how you're seeing it with two backslashes, but it really only has one. Are you still looking in the debugger?

[Sandeep]

Ok. If it's really just a single slash, then why is this string not getting replaced in the text file??? Do I need to do something else to replace these kind of things??

[Jon Skeet]

@user762730: You haven't shown us the code you're using to perform the replacement, so we can't tell what's wrong.

[Sandeep]

Solved the issue... The problem was with the Replace I was doing. I was performing a Regex.Replace. Instead, I should have used string.Replace method... Regex.Replace(stringToBeReplaced, @"\\", @"\") doesn't work.. stringToBeReplaced.Replace(@"\\", @"\") WORKS...!!!!

[Jon Skeet]

@user762730: If stringToBeReplaced is really declared as shown in your sample code, that doesn't make sense - because the code you've got really only has one backslash. Perhaps it isn't really representative of your real code?

[Pierre]

"my\\r\\nstring".Replace(@"\r\n", "\r\n") works. Notice only the text to replace has the @ infront of it

[CEH]

While this code-only answer may solve the issue in the question, adding an explanation will help other users understand the solution and improve the quality.