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character to use when splitting strings in visual c#?

Ok, I'm racking my brains over this one. It's pretty simple though (I think).
I'm currently creating a text file as a comma separated string of values.
Later, I read in that file data and then use the .split function to split the data by commas.
I discovered that sometimes one of the description fields in the data conatins an embedded comma, which ends up throwing the split command off.
Is there any special character I could use that could pretty much guarantee wouldn't be in the data, or is there a better way to accomplish this? Thanks!
// Initial Load
fullString = fileName + "," + String.Join(",", fieldValues);
// Access later
String[] valuesArray = myString.Split(',');

Short answer, there's no "simple" way to do it using Split. The best you can hope for is to set the deliminator as something cooky that wouldn't ever get used (but even that's not a guarantee).
The simple method would be to used something like CsvHelper (get it through Nuget) or any of the other dozen or so packages that are designed for parsing CSV.

C# NewLine inside File.AppendAllText

Writing a simple log for a program I'm doing and I'm getting troubles with FileAppendText()
I have this line to output various messages to the log:
File.AppendAllText( filePath, string.Format( "{0} {1}{2}", DateTime.Now, message, Environment.NewLine ) );
Problem with this is when I try to use it with a string like this
"This is my first line, \r\n this is my second line \r\n and this is my final line!"
It will just give this result
This is my first line, this is my second line and this is my final line!
when it should be
This is my first line,
this is my second line
and this is my final line!
Is there a way to fix this or do I have to do some dirty fixes?

File.AppendAllText does not modify the string that you pass in. You miust be misinterpreting what you are seeing.
Probably, the tool that you use to look at the file contents has a special way of showing them. It does not support rendering newlines. Use notepad.exe.
Maybe the question is based on wrong data. When you write line, \r\n this you should get two spaces. But your sample text does not have two spaces (line, this). Are you even showing us the exact thing you passed in and got out?!

I resolved the same problem using Environment.NewLine instead of \r\n.

Deleting line breaks in a text file with a condition

I have a text file. Some of the lines in it end with lf and some end with crlf. I only need to delete lfs and leave all crlfs.
Basically, my file looks like this
Mary had a lf
dog.crlf
She liked her lf
dog very much. crlf
I need it to be
Mary had a dog.crlf
She liked her dog very much.crlf
Now, I tried just deleting all lfs unconditionally, but then I couldn't figure out how to write it back into the text file. If I use File.WriteAllLines and put a string array into it, it automatically creates line breaks all over again. If I use File.WriteAllText, it just forms one single line.
So the question is - how do I take a text file like the first and make it look like the second? Thank you very much for your time.
BTW, I checked similar questions, but still have trouble figuring it out.

Use regex with a negative look-behind and only replace the \n not preceded by a \r:
DEMO
var result = Regex.Replace(sampleFileContent, #"(?<!\r)\n", String.Empty);
The (?<! ... ) is a negative look-behind. It means that we only want to replace instances of \n when there isn't a \r directly behind it.
Disclaimer: This may or may not be as viable an option depending on the size of your file(s). This is a good solution if you're not concerned with overhead or you're doing some quick fixes, but I'd look in to a more robust parser if the files are going to be huge.

This is an alternative to Brad Christie's answer, which doesn't use Regex.
String result = sampleFileContent.Replace("\r\n", "**newline**")
.Replace("\n","")
.Replace("**newline**","\r\n");
Here's a demo. Seems faster than the regex solution according to this site, but uses a bit more memory.

Just tested it:
string file = File.ReadAllText("test.txt");
file = file.Replace("\r", "");
File.WriteAllText("test_replaced.txt", file);

c# equivalent to stripcslashes function?

I am working with a project that includes getting MMS from a mms-gateway and storing the image on disk.
This includes using a received base64encoded string and storing it as a zip to a web server. This zip is then opened, and the image is retrieved.
We have managed to store it as a zip file, but it is corrupted and cannot be opened.
The documentation from the gateway is pretty sparse, and we have only a php example to rely on. I think we have figured out how to "translate" most of it, except for the PHP function stripcslashes(inputvalue). Can anyone shed shed any light on how to do the same thing in c#?
We are thankful for any help!

stripcslashes() looks for "\x" type elements within longer strings (where 'x' could be any character, or perhaps, more than one). If the 'x' is not recognised as meaningful, it just removes the '\' but if it does recognise it as a valid C-style escape sequence (i.e. "\n" is newline; "\t" is tab, etc.), as I understand it, the recognised character is inserted instead: \t will be replaced by a tab character (0x09, I think) in your string.
I'm not aware of any simple way to get the .net framework to do the same thing without building a similar function yourself. This obviously isn't very hard, but you need to know which escape sequences to process.
If you happen to know (or find out by inspecting your base64 text) that the only thing in your input that will need processing is a particular one or two sequences (say, tab characters), it becomes very easy and the following snippet shows use of String.Replace():
string input = #"Some\thing"; // '#' means string stored without processing '\t'
Console.WriteLine(input);
string output = input.Replace(#"\t", "\t");
Console.WriteLine(output);
Of course, if you really do simply want to remove all the slashes:
string output = input.Replace(#"\", "");

How do I write escape characters verbatim (without escaping) using StreamWriter?

I'm writing a utility that takes in a .resx file and creates a javascript object containing properties for all the name/value pairs in the .resx file. This is all well and good, until one of the values in the .resx is
This dealer accepts electronic orders.
/r/nClick to order {0} from this dealer.
I'm adding the name/value pairs to the js object like this:
streamWriter.Write(string.Format("\n{0} : \"{1}\"", kvp.Key, kvp.Value));
When kvp.Value = "This dealer accepts electronic orders./r/nClick to order {0} from this dealer."
This causes StreamWriter.Write() to actually place a newline in between 'orders.' and 'Click', which naturally screws up my javascript output.
I've tried different things with # and without using string.Format, but I've had no luck. Any suggestions?
Edit: This application is run during build to get some javascript files deployed later, so at no point is it accessible to / run by anyone but the app developers. So while I obviously need a way to escape characters here, XSS as such is not really a concern.

Your problem has already happened by the time you get to this code. String.Format will not "expand" literal \n and \r in the substituted strings ({0} etc) into newline and CR, so it must have happened at some earlier point, possibly while reading the .resx file.
You have two possible solutions. One, as you discovered in the comments to DonaldRay's answer, is to explicitly reverse this replacement, and replace literal newlines with the two characters \n:
kvp.Value.Replace("\r", // <-- replaced by the C# compiler with a literal CR character
"\\r"); // <-- "\\" replaced by the C# compiler with a single "\",
// leaving the two-char string "\r"
You will need to do the same for every character that could appear in your strings. \n and \r are the most common, and then \t (tab); that's probably enough for most dev tools.
string formatted = kvp.Value.Replace("\r", "\\r")
.Replace("\n", "\\n")
.Replace("\t", "\\t");
Alternatively, you could look upstream at the .resx file reading code, and try to find and remove the part that's explicitly expanding these character sequences. This would be a better general solution, if it's possible.

You need to escape the strings, using Microsoft's Anti-XSS Library.

Just escape the backslashes.
kvp.Value = kvp.Value.Replace(#"\", #"\\");
You may need to do this when you are reading from the resx file.