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How do I use C#'s IndexOf when strange characters are in the string

Below is what the text looks like when viewed in NotePad++.
I need to get the IndexOf for that peice of the string. for use the the below code. And I can't figure out how to use the odd characters in my code.
int start = text.IndexOf("AppxxxxxxDB INFO");
Where the "xxxxx"'s represent the strange characters.

All these characters have corresponding ASCII codes, you can insert them in a string by escaping it.
For instance:
"App\x0000\x0001\x0000\x0003\x0000\x0000\x0000DB INFO"
or shorter:
"App\x00\x01\x00\x03\x00\x00\x00"+"DB INFO"
\xXXXX means you specify one character with XXXX the hexadecimal number corresponding to the character.
Notepad++ simply wants to make it a bit more convenient by rendering these characters by printing the abbreviation in a "bubble". But that's just rendering.
The origin of these characters is printer (and other media) directives. For instance you needed to instruct a printer to move to the next line, stop the printing job, nowadays they are still used. Some terminals use them to communicate color changes, etc. The most well known is \n or \x000A which means you start a new line. For text they are thus characters that specify how to handle text. A bit equivalent to modern html, etc. (although it's only a limited equivalence). \n is thus only a new line because there is a consensus about that. If one defines his/her own encoding, he can invent a new system.

Echoing #JonSkeet's warning, when you read a file into a string, the file's bytes are decoded according to a character set encoding. The decoder has to do something with bytes values or sequences that are invalid per the encoding rules. Typical decoders substitute a replacement character and attempt to go on.
I call that data corruption. In most cases, I'd rather have the decoder throw an exception.
You can use a standard decoder, customize one or create a new one with the Encoding class to get the behavior you want. Or, you can preserve the original bytes by reading the file as bytes instead of as text.
If you insist on reading the file as text, I suggest using the 437 encoding because it has 256 characters, one for every byte value, no restrictions on byte sequences and each 437 character is also in Unicode. The bytes that represent text will possibly decode the same characters that you want to search for as strings, but you have to check, comparing 437 and Unicode in this table.
Really, you should have and follow the specification for the file type you are reading. After all, there is no text but encoded text, and you have to know which encoding it is.

Special characters for Docx with ooxml

I am converting HTML to docx using http://www.codeproject.com/Articles/91894/HTML-as-a-Source-for-a-DOCX-File.
Most of the characters are read properly but some special characters such as •,“ ” are being displayed as •. What should I be doing to correct this?
The HTML that I was passing to HTMLtoDocx was also not reading special characters properly. Instead it was displaying as '?'. After changing the encoding to Encoding.Default it's returning the correct characters.
In HTMLtoDOCX there are two places that I can set encoding(lines below). In both the places I Tried changing the encoding format from Encoding.UTF8 to Encoding. But it isn't helping.
StreamWriter streamStartPart = new StreamWriter(docpartDocumentXML.GetStream(FileMode.Create, FileAccess.Write), Encoding.Default);
byte[] Origem = Encoding.Default.GetBytes(html);

• indicates a UTF-8 sequences incorrectly interpreted as ANSI (=Encoding.Default).
You should check whether the HTML file is read with the correct encoding.
While the encoding info is available in the HTTP Header or in HTML META tags, this encoding may not be correct if the HTML is read from a file.
Since .Net treats string characters as 2-byte Unicode values, making sure the correct encoding is apply to read and write byte streams is the first step to fix your problem.

Read mixed encoding string

I read some string with (windows-1256) encoding but the numbers in that string encoded using (UTF-8) and as a result all text except numbers (encoded with utf-8) read but numbers displays as (?) which is acceptable. but i want to know how can i read complete text without problem, how can i know when to switch between encodings to read correct text.
NOTE: Browsers displays these kind of text correctly so they know when they should switch
Any solution or code ?

The lower half of the windows-1256 code page is the same as ASCII. Digits in UTF-8 are also the same as ASCII - if you read the string with windows-1256 encoding, it should work just fine.

Weird character "Â" before degrees Celcius symbol "°C"

I asked this question a day ago regarding Greek Unicode characters, and now I have a question which builds upon that one.
After extracting all my data, I have attempted to prepare it for import into Excel. I had to chose a tab delimited file because some of my data contains commas (lucky me!).
The issue I'm running into is a very weird character after I import the data into Excel.
The column data in Notepad++ looks like this:
Total Suspended Solids #105°C
The Excel cell data looks like this:
Total Suspended Solids #105°C
I don't understand why this is happening. Does this have something to do with how the degrees symbol is represented?
p.s. I the symbols in this question are direct copy and paste

(More likely) Excel is interpreting your textual data as latin-1 or windows-1252, and not UTF-8. "°" is what you get if you take the UTF-8 bytes for "°" (0xc2 0xb0) and interpret each byte as a character of latin-1 or windows-1252. Is there an option for input encoding when you do your import?
(Less likely) Excel is doing the right thing, but you're double-encoding your data (encoding as UTF-8, then re-interpreting it as an 8-bit encoding and encoding again as UTF-8 or any other Unicode encoding). Notepad++ evidence is against this one.

I'm not absolutely sure, but I think Excel expects Windows-1252 character encoding, so make sure you create your text file using Encoding.GetEncoding("Windows-1252").
For example:
using (var writer = new StreamWriter(fileName,false,Encoding.GetEncoding("Windows-1252"))
{
....
}

You can use UTF-8 BOM for your file.

How to get correctly-encoded HTML from the clipboard?

Has anyone noticed that if you retrieve HTML from the clipboard, it gets the encoding wrong and injects weird characters?
For example, executing a command like this:
string s = (string) Clipboard.GetData(DataFormats.Html)
Results in stuff like:
<FONT size=-2>  <A href="/advanced_search?hl=en">Advanced
Search</A><BR>  Preferences<BR>  <A
href="/language_tools?hl=en">Language
Tools</A></FONT>
Not sure how MarkDown will process this, but there are weird characters in the resulting markup above.
It appears that the bug is with the .NET framework. What do you think is the best way to get correctly-encoded HTML from the clipboard?

In this case it is not so visible as it was in my case. Today I tried to copy data from clipboard but there were a few unicode characters. The data I got were as if I would read a UTF-8 encoded file in Windows-1250 encoding (local encoding in my Windows).
It seems you case is the same. If you save the html data (remember to put non-breakable space = 0xa0 after the  character, not a standard space) in Windows-1252 (or Windows-1250; both works). Then open this file as a UTF-8 file and you will see what there should be.
For my other project I made a function that fix data with corrupted encoding.
In this case simple conversion should be sufficient:
byte[] data = Encoding.Default.GetBytes(text);
text = Encoding.UTF8.GetString(data);
My original function is a little bit more complex and contains tests to ensure that data are not corrupted...
public static bool FixMisencodedUTF8(ref string text, Encoding encoding)
{
if (string.IsNullOrEmpty(text))
return false;
byte[] data = encoding.GetBytes(text);
// there should not be any character outside source encoding
string newStr = encoding.GetString(data);
if (!string.Equals(text, newStr)) // if there is any character "outside"
return false; // leave, the input is in a different encoding
if (IsValidUtf8(data) == 0) // test data to be valid UTF-8 byte sequence
return false; // if not, can not convert to UTF-8
text = Encoding.UTF8.GetString(data);
return true;
}
I know that this is not the best (or correct solution) but I did not found any other way how to fix the input...
EDIT: (July 20, 2017)
It Seems like the Microsoft already found this error and now it works correctly. I'm not sure whether the problem is in some frameworks, but I know for sure, that now the application uses a different framework as in time, when I wrote the answer. (Now it is 4.5; the previous version was 2.0)
(Now all my code fails in parsing the data. There is another problem to determine the correct behaviour for application with fix already aplied and without fix.)

You have to interpret the data as UTF-8. See MS Office hyperlinks change code page?.

DataFormats.Html specification states it's encoded in UTF-8. But there's a bug in .NET 4 Framework and lower, and it actually reads as UTF-8 as Windows-1252.
You get allot of wrong encodings, leading funny/bad characters such as
'Å','‹','Å’','Ž','Å¡','Å“','ž','Ÿ','Â','¡','¢','£','¤','Â¥','¦','§','¨','©'
Full explanation here
Debugging Chart Mapping Windows-1252 Characters to UTF-8 Bytes to Latin-1 Characters
Soln: Create a translation dictionary and search and replace.

I don't know what your original source document is, but be aware that Word and Outlook provide several versions of the clipboard in different encodings. One is usually Windows-1252 and another is UTF-8. Possibly you're grabbing the UTF-8 encoded version by default, when you're expecting the Windows-1252 (Latin-1 + Smart Quotes)? Non-ASCII characters would show up as multiple odd Latin-1 accented characters. Most "Smart Quotes" are not in the Latin-1 set and are often three bytes in UTF-8.
Can you specify which encoding you want the clipboard contents in?

Try this:
System.Windows.Forms.Clipboard.GetText(System.Windows.Forms.TextDataFormat.Html);