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Why are some unintended symbols added to my string?

I wrote a console application which fetches strings from some fields in a Sharepoint list. Then I simply write the strings to console. This works fine for the most fields. There is one MultiLineTextField with RichText enabled where i had to remove all the html-tags, that causes this issue.
Even after all the tags are removed the strings seem to contain question marks which were never added to the string. The most weird thing about this is when I set a breakpoint and look into the string's value there are no question marks, but they suddenly appear on the console output.
The only thing I could think of was to Trim the string. Because sometimes they appear in front of the actual string sometimes they are at the and of it, but never in between.
So this is what I tried:
myString = myString.Trim();
myString = myString.Replace("?",string.Empty);
But this does not solve the issue. Besides this would not be a smart solution in case one of the strings would be supposed to contain question marks. For detailed code please see the link above.
Also Convert.ToBase64String(Encoding.UTF8.GetBytes(myString)) gives me the following output:
4oCLTWVobCwgRWllciwgV2Fzc2VyLCBIYWNrZmxlaXNjaCA=

There are probably some non-printing unicode (or possibly low ASCII) characters in the end of the string. The console has a different encoding, and will often render such as ?. Basically: use the indexer (yourString[n]) or yourString.ToCharArray() to investigate what is actually in the string aroung the location of the ?.
With the edit, we can see that the string has a zero-width space (decimal 8203) at the start:

Sounds like you're maybe having a problem with unicode characters. Chances are you're outputting the string as ASCII instead of Unicode. Take a look at this question as it sounds like you may be experiencing the same problem.

line break in alert popup

I am trying to add a new line Javascript alert message. I tried '\n' and 'Environment.NewLine'. I am getting Unterminated string constant error. Could you please let me know what could be the problem? I appreciate any help. I also tried \r\n.
string msg = "Your session will expire in 10 minutes. \n Please save your work to avoid this.";
if (!this.ClientScript.IsStartupScriptRegistered(ID))
this.ClientScript.RegisterStartupScript(GetType(), ID, String.Format("<script language=JavaScript>setTimeout(\'alert(\"{1}\");\',{0}*1000);</script>", sTime, msg));

I would suspect that you need to change your code to;
string msg = "Your session will expire in 10 minutes. \\n Please save your work to avoid this.";
And escape the \n otherwise your code outputted would actually include the line break rather than \n
Your output code would look like:
setTimeout('alert("Your Session....
Please save your work to ....");', 1000);
Rather than:
setTimeout('alert("Your Session....\n Please save your work to ....");', 1000);

I'm not sure, but I think that \n is escaped in the string.Format method, like \". Maybe you should use \\n instead.
Edited : and the first \ of \\n has been escaped when i posted that. xD

At first glance I would say the primary problem is that you're escaping the ' character around your alert. Since your string is defined by the double quotes, you don't need to escape this character.

add "#" at the beginning of your string - like this:
string msg = #"Your session ....";

The code looks fine, so I'm going to guess that you're using a message that itself has a ' quote in it, causing the JS syntax error. For inserting dynamic text into a Javascript code block, you really should use JSON to make your C# strings 'safe' for use in JS.
Consider JSON the go-to method for preventing the JS equivalent of SQL injection attacks.

Adding a # at the beginning should help.

Escaping directory chars in C#

I need to escape chars in a string I have, which content is C:\\blablabla\blabla\\bla\\SQL.exe to C:\blablabla\blabla\bla\SQL.exe so I could throw a process based on this SQL.exe file.
I tried with Mystring.Replace("\\", #"\"); and Mystring.Replace(#"\\", #"\"); but none worked.
How could I do this?
EDITED: Corrected type in string.

I very strongly suspect that you are looking this input string in the Visual Studio debugger and fooling yourself that there are actually 2 \ whereas in reality there aren't. That's the reason why attempting to replace \\ with \ doesn't do anything because in the original string there is no occurrence of \\. And since you are looking the output once again in the debugger, you are once again fooling yourself that there are 2 \.
Visual Studio debugger has this tendency to escape strings. Log it to a file or print to the console and you will see that there is a single \ in your input string and you don't need to replace anything.

It looks like you're trying to replace double backslash (#"\\") in a string with single backslash (#"\"). If so try the following
Mystring = Mystring.Replace(#"\\", #"\");
Note: Are you sure that the string even contains double backslashes? Certain environments will print out a single backslash as a double (debugger for example). Your comment mentioned my approach didn't work. That's a flag that there's not actually a double backslash in your string (else it would work).

The # character specifies a string as a verbatim literal string, but that is when constructing a string. If you use Mystring.Replace("\\", #"\") then nothing will be replaced, essentially, as the two strings are the same.
If you want a string without the escape characters, then either define it with:
string path = #"C:\Some\Directory\And\File.txt";
Or you can replace the \\ with / like so:
path = path.Replace('\\', '/');
It is worth noting, as mentioned by Darin Dimitrov, that the string containing two \ characters is likely just the display of the string (i.e. when using the debugger) and not the actual value of the string.

i think OP is asking how to escape \\ in File Path, if that in the case, as OP is not mentioning where he's trying to use this. so i'm putting a guess.
Then You use Path.Combine() method to get the FileName path.
Path.Combine() Documentation

where are you looking at this output? because it could be the string is what you expect, but viewing the value through the debugger, output window, etc. is escaping the slash

Use something like:
myStr = myStr.Replace(#"\\", #"\");
Make sure you assign the result of Replace method to myStr. Otherwise it goes into void ;)

Try adding "|DataDirectory|\MyFile.xyz" where you need it. It works with connection strings it might work with something else (I haven't really tried to apply it to something else).

I didn't understand what you want, if you just want do get the file name (escape directory chars) you can try:
string fileName = Path.GetFileName(YourString)

Noloman.... when you concatenate are you perhaps missing a "\" when concatenating the directory.. I am assuming that you are trying to join directory + some sub directory.. #noloman keep in mind that in C# "c:\Temp" is written like this "c:\Temp" or #"c:\Temp" one is Literal the other is how to represent a "\" in the legacy way of coding because the "\" is an escape Char and when dealing with directorys we represent all paths and sub paths with "\"
so perhaps by you replacing the "\" you are truly messing up your own expected process
Mystring = Mystring.Replace(#"\\", #"\");
should work for you unless you are truly meaning to do
Mystring = Mystring.Replace(#"\", "\"); which if you believe that you are expecting a "\" to be used to build the directory.. then of course it will not work.. because you have just in essense replaced the backslash with a return char.. I hope that this makes sense to you..
System.IO.Directory.GetCurrentDirectory(); you are using is also an Issue.. SQL Server is not that application thats running the code.. it's your .NET application so you need to either put the location of the SQL Server into a variable, app.config, web.config ect... please edit your question and paste the code that you are using to do what it is that you want to do inregards to the SQL Server Code.. you would probably want to look at the Are you wanting to do something like Process.Start(....) meaning the file name..?

formatting strings with backslash

I'm a newbie to c# so hopefully this one isn't too hard for a few of you.
I'm trying to build a string that has a \ in it and I am having difficulty getting just one backslash to show up even though I am adding additional escape chars or ignoring them all together. Can someone show me what I am doing wrong?
What I want my string to look like:
"10.20.14.103\sql08"
What I've tried so far:
I added an additional character to make the compiler happy but it did not escape it.
ip = string.Format("{0}\\\\{1}", ip, instancename); // output has 2 \'s
I told it to ignore escapes, it decided to ignore me instead
string temp = #"192.168.1.200\sql08"; // output has 2 \'s
Can someone help me make sense of this? (The richtext editor here seems to do a better job with it than VS2010 is doing, lol)

I'm guessing you're getting confused by the debugger.
If you hover your mouse over a local variable in VS, strings will be escaped so a single \ will display as \\.
To see what your string really is, output it somewhere for display (e.g., to the console) or hover your mouse on the variable, click on the arrow next to the little magnifying glass that appears, and select "Text Visualizer."

If you're looking at these strings in the debugger (i.e., by hovering the mouse over the variable or using a watch), the debugger adds escape characters to the display string so that it's a valid string expression. If you want to view the string verbatim in this fashion, click on the magnifying glass on the right side of the tooltip or watch entry with the string in it.

I'm guessing you're looking at the values in the debugger and seeing that they have two slashes.
That's normal. The debugger will show two slashes even though the actual string representation will only have one. Just another hump to get over when getting used to the debugger.
Be assured that when you actually use your strings, they will still only have a single slash (using either of your methods).

string requiredString = string.Format(#"{0}\\{1}",str1,str2);

Newlines escaped unexpectedly in C#/ASP.NET 1.1 code

Can someone explain to me why my code:
string messageBody = "abc\n" + stringFromDatabaseProcedure;
where valueFromDatabaseProcedure is not a value from the SQL database entered as
'line1\nline2'
results in the string:
"abc\nline1\\nline2"
This has resulted in me scratching my head somewhat.
I am using ASP.NET 1.1.
To clarify,
I am creating string that I need to go into the body of an email on form submit.
I mention ASP.NET 1.1 as I do not get the same result using .NET 2.0 in a console app.
All I am doing is adding the strings and when I view the messageBody string I can see that it has escaped the value string.
Update
What is not helping me at all is that Outlook is not showing the \n in a text email correctly (unless you reply of forward it).
An online mail viewer (even the Exchange webmail) shows \n as a new line as it should.

I just did a quick test on a test NorthwindDb and put in some junk data with a \n in middle. I then queried the data back using straight up ADO.NET and what do you know, it does in fact escape the backslash for you automatically. It has nothing to do with the n it just sees the backslash and escapes it for you. In fact, I also put this into the db: foo"bar and when it came back in C# it was foo\"bar, it escaped that for me as well. My point is, it's trying to preserve the data as is on the SQL side, so it's escaping what it thinks it needs to escape. I haven't found a setting yet to turn that off, but if I do I'll let you know...

ASP.NET would use <br /> to make linebreaks. \n would work with Console Applications or Windows Forms applications. Are you outputting it to a webpage?
Method #1
string value = "line1<br />line2";
string messageBody = "abc<br />" + value;
If that doesn't work, try:
string value = "line1<br>line2";
string messageBody = "abc<br>" + value;
Method #2
Use System.Environment.NewLine:
string value = "line1"+ System.Environment.NewLine + "line2";
string messageBody = "abc" System.Environment.NewLine + value;
One of these ways is guaranteed to work. If you're outputting a string to a Webpage (or an email, or a form submit), you'd have to use one of the ways I mentioned. The \n will never work there.

You need to set a watch and see where exactly your database result string gets double escaped.
Adding two strings together will never double escape strings, so its either happening before that, or after that.

When I get the string out of the database, .NET escapes it automagically. However, the little # symbol is appended to the string, which I did not notice.
So it appeared to be non-escaped to my "about to go on holiday" eye inside the ide.
Therefore when the non-escaped \n was added to the string (as the whole string is no longer escaped), it would remove the # and show the database portion of the string escaped.
Gah, it was all an illusion.
Perhaps that holiday is overdue.
Thanks for your input.

If the actual string stored in the database is (spaces added for emphasis): "l i n e 1 \ n l i n e 2", then whatever stored it there probably has a bug. But assuming that is the exact string there, then the "abc\nline1\nline2" string is what happens when you look at the string which would print as "abcline1\nline2" in a debugger which escapes it (this is a convenience, allowing you to copy-paste out of the debugger straight into code without errors).
Short answer: .NET is not escaping the string, your debugger is. The code which writes a literal "\n" into the database has a bug.