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How to decode a utf string in c#

I have been trying to decode the following string:
Crédit
in c# using the following code:
Encoding iso = Encoding.GetEncoding("ISO-8859-1");
Encoding utf8 = Encoding.UTF8;
string msg = iso.GetString(utf8.GetBytes(#"Crédit"));
which is yielding:
Crédit
I looked online http://jeppesn.dk/utf-8.html and this is in correct utf 8 and should yield:
Crédit
Can someone please point out where i am going wrong?
Thanks

It should be the other way around, and Windows-1252, not ISO-8859-1. Depending on context, people usually mean Windows-1252 when they say Latin-1 or ISO-8859-1, but actually using ISO-8859-1 will fail when there are characters like € because it was a mislabeling in the first place. Even browsers use Windows-1252 when ISO-8859-1 is specified as encoding.
Encoding w1252 = Encoding.GetEncoding(1252);
Encoding utf8 = Encoding.UTF8;
string msg = utf8.GetString(w1252.GetBytes(#"Crédit"));

You're trying to do something that doesn't make sense, basically. You should almost never1 be interpreting the output of one encoding as the input to another encoding. It's like saying, "Suppose I save this image as a gif... then load that file using a jpeg loader... what does it look like?"
I suspect that if you use:
// Just an example: don't actually do this.
string msg = utf8.GetString(iso.GetBytes(#"Crédit"));
... it will do what you want, but you shouldn't be doing this at all.
Now, what is your real input (in what form) and what are you trying to achieve?
1 If you're doing so, it's usually because someone else has already done the wrong thing, or there's a configuration problem somewhere. If you find yourself doing this, you should think very carefully about whether you should really be doing it, or whether you're just working around a different problem which should be tackled differently.

Is there cross-platform method to encode a string into another string without any whitespaces and then decode it back?

I am trying to pass a block of text to a system I do not own, which will pass the data to a system I do own.
Unfortunately, when the first system talks to the second system, it uses a TSV format. Thus, I wonder if there's a convenient way to take my block of text and encode it in an ASCII format without any kind of whitespace (mostly newlines and tabs, of course), and then later decode it.
When I'm doing the encoding, I'm working in C#. When I'm doing the decoding, I'm working in Javascript.
I realize that I can write my own code to essentially "manually" perform the encoding and decoding by creating my own scheme, but I wonder if there already exists one for this purpose.

One option which would blow up the size of your data but be really simple to implement: UTF-8 encode all the text, base64-encode that:
byte[] utf8 = Encoding.UTF8.GetBytes(text);
string base64 = Convert.ToBase64(utf);
That won't contain any whitespace, and can be converted back. It'll be significantly larger than the original string, and unreadable... but it'll work.

You could try using HttpUtility.UrlEncode(string) or Uri.EscapeDataString(string), which would percent-encode any whitespace in the passed in text (as well as other special characters, which means the encoded text may be much larger than the original).
On the javascript side you could then use decodeURIComponent(string) to decode it back to the original text.

Decoding Base64 / Quoted Printable encoded UTF8 string

In my ASP.Net application working process, I need to do some work with string, which equals something like
=?utf-8?B?SWhyZSBCZXN0ZWxsdW5nIC0gVmVyc2FuZGJlc3TDpHRpZ3VuZyAtIDExMDU4OTEyNDY=?=
How can I decode it to normal human language?
Thanks in advance!
Update:
Convert.FromBase64String() does not work for string, which equals
=?UTF-8?Q?Bestellbest=C3=A4tigung?=
I get The format of s is invalid. s contains a non-base-64 character, more than two padding characters, or a non-white space-character among the padding characters. exception.
Update:
Solution Here
Alternative solution
Update:
What kind of string encoding is that: Nweiß ???

It's actually a base-64 string:
string zz = "SWhyZSBCZXN0ZWxsdW5nIC0gVmVyc2FuZGJlc3TDpHRpZ3VuZyAtIDExMDU4OTEyNDY=";
byte[] dd = Convert.FromBase64String(zz);
// Returns Ihre Bestellung - Versandbestätigung - 1105891246
string yy = System.Text.Encoding.UTF8.GetString(dd);

I've written a library that will decode these sorts of strings. You can find it at http://github.com/jstedfast/MimeKit
Specifically, take a look at MimeKit.Utils.Rfc2047.DecodeText()

This seems to be MIME Header Encoding. The Q in your second example indicates that it is Quoted Printable.
This question seems to cover the variants fairly well. In a quick search I didn't find any .NET libraries to decode this automatically, but it shouldn't be hard to do manually if you need to.

That's not UTF8. Thats a Base64 encoded string.
the UTF-8 only indicates that the target string is in UTF8 format.
After decoding the Base64 string:
SWhyZSBCZXN0ZWxsdW5nIC0gVmVyc2FuZGJlc3TDpHRpZ3VuZyAtIDExMDU4OTEyNDY=
You'll get the following result:
Ihre Bestellung - Versandbestätigung - 1105891246
See Base64 online decode/encode

Looks like a base64 string.
Try Convert.FromBase64String
http://msdn.microsoft.com/en-us/library/system.convert.frombase64string.aspx

This is an encoded word, which is used in email headers when there is non-ASCII content. Encoded words are defined in RFC 2047:
https://www.rfc-editor.org/rfc/rfc2047#section-2
The BNF for an encoded word is:
encoded-word = "=?" charset "?" encoding "?" encoded-text "?="
So the correct way to interpret this is:
The data is the stuff between the 3rd and 4th question marks
It has been Base64 encoded (the 'B' stands for Base64; if it were a
'Q' then it would be quoted-printable).
Once you decode the
data, it will be in the UTF-8 character set.
The result, as #Shai correctly pointed out, is:
Ihre Bestellung - Versandbestätigung - 1105891246
This is German. The umlaut is obviously the reason for the UTF-8 and thus the need for an encoded word. The translation is:
Your order - Delivery confirmation - 1105891246
Apparently it's a tracking number for an order.
All modern email clients (and Outlook) transparently support encoded words.

This is a bit of guesswork, but let's try
remove =? from start and ?= from end
keep the start up to the next ? as the character set
Remove the B? - don't know, what it is
Convert the rest to a byte[] via System.Convert.FromBase64String()
Convert this to the final String via Encoding.GetSTring() using the character set remembered in the second step

Convert UCS-2 characters to UTF-8 Using C#

I'm pulling some internationalized text from a MS SQL Server 2005 database. As per the defaults for that DB, the characters are stored as UCS-2. However, I need to output the data in UTF-8 format, as I'm sending it out over the web. Currently, I have the following code to convert:
SqlString dbString = resultReader.GetSqlString(0);
byte[] dbBytes = dbString.GetUnicodeBytes();
byte[] utf8Bytes = System.Text.Encoding.Convert(System.Text.Encoding.Unicode,
System.Text.Encoding.UTF8, dbBytes);
System.Text.UTF8Encoding encoder = new System.Text.UTF8Encoding();
string outputString = encoder.GetString(utf8Bytes);
However, when I examine the output in the browser, it appears to be garbage, no matter what I set the encoding to.
What am I missing?
EDIT:
In response to the answers below, the reason I thought I had to perform a conversion is because I can output literal multibyte strings just fine. For example:
OutputControl.Text = "カルフォルニア工科大学とチューリッヒ工科大学は共同で、太陽光を保管可能な燃料に直接変えることのできる装置の開発に成功したとのこと";
works. Here, OutputControl is an ASP.Net Literal. However,
OutputControl.Text = outputString; //Output from above snippet
results in mangled output as described above. My hypothesis was that the database's output was somehow getting mangled by ASP.Net. If that's not the case, then what are some other possibilities?
EDIT 2:
Okay, I'm stupid. It turns out that there's nothing wrong with the database at all. When I tried inserting my own literal double byte characters (材料,原料;木料), I could read and output them just fine even without any conversion process at all. It seems to me that whatever is inserting the data into the DB is mangling the characters somehow, so I'm going to look at that. With my verified, "clean" data, the following code works:
OutputControl.Text = dbString.ToString();
as the responses below indicate it should.

Your code does essentially the same as:
SqlString dbString = resultReader.GetSqlString(0);
string outputString = dbString.ToString();
string itself is a UNICODE string (specifically, UTF-16, which is 'almost' the same as UCS-2, except for codepoints not fitting into the lowest 16 bits). In other words, the conversions you are performing are redundant.
Your web app most likely mangles the encoding somewhere else as well, or sets a wrong encoding for the HTML output. However, that can't be diagnosed from the information you provided so far.

String in .net is 'encoding agnostic'.
You can convert bytes to string using a particular encoding to tell .net how to interprets your bytes.
You can convert string to bytes using a particular encoding to tell .net how you want your bytes served.
But trying to convert a string to another string using encodings makes no sens at all.

C# Byte[] to Url Friendly String

I'm working on a quick captcha generator for a simple site I'm putting together, and I'm hoping to pass an encrypted key in the url of the page. I could probably do this as a query string parameter easy enough, but I'm hoping not too (just because nothing else runs off the query string)...
My encryption code produces a byte[], which is then transformed using Convert.ToBase64String(byte[]) into a string. This string, however, is still not quite url friendly, as it can contain things like '/' and '='. Does anyone know of a better function in the .NET framework to convert a byte array to a url friendly string?
I know all about System.Web.HttpUtility.UrlEncode() and its equivalents, however, they only work properly with query string parameters. If I url encode an '=' inside of the path, my web server brings back a 400 Bad Request error.
Anyways, not a critical issue, but hoping someone can give me a nice solution
**EDIT: Just to be absolutely sure exactly what I'm doing with the string, I figured I would supply a little more information.
The byte[] that results from my encryption algorithm should be fed through some sort of algorithm to make it into a url friendly string. After this, it becomes the content of an XElement, which is then used as the source document for an XSLT transformation, and is used as a part of the href attribute for an anchor. I don't believe the xslt transformation is causing the issues, since what is coming through on the path appears to be an encoded query string parameter, but causes the HTTP 400
I've also tried HttpUtility.UrlPathEncode() on a base64 string, but that doesn't seem to do the trick either (I still end up with '/'s in my url)**

You're looking for HttpServerUtility.UrlTokenEncode and HttpServerUtility.UrlTokenDecode, in System.Web.
They encode in base64, replacing the potentially dangerous '+' and '/' chars with '-' and '_' instead.
MSDN documentation

For ASP.NET Core 6.0+ use Microsoft.AspNetCore.WebUtilities.WebEncoders:
byte[] bytes = RandomNumberGenerator.GetBytes(64);
string encoded = WebEncoders.Base64UrlEncode(bytes);
byte[] decoded = WebEncoders.Base64UrlDecode(encoded);

Have a look at System.BitConverter.ToString(myByteArray)
Handy for one way encoding for things like hashes but as pointed out by ssg it's not very efficient. I wouldn't recommend it for large amounts of data.

HttpServerUtility.UrlTokenEncode and similar are no longer available in .NET Core as of .NET 6.
The following method should provide an RFC4648§5-compliant base64 string based on a quick reading.
This code allocates at least four objects on the heap, so ultra-high performance use cases should tune it a bit and perhaps wait for .NET 7, which is expected to introduce a means to get the random bytes into a Span for stack allocation.
private string GetUrlSafeRandomBytes(int byteCount)
{
var salt = new byte[byteCount];
using var rng = RandomNumberGenerator.Create();
rng.GetBytes(salt);
var asBase64 = Convert.ToBase64String(salt);
var asUrlSafeString = asBase64.Replace('+', '-').Replace('/', '_');
return asUrlSafeString;
}