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C# file readline has double back slashes reading a text file

I get the answers in the following topic/question:
Reading a line from text file returns unwanted slash
the answer states:
The debug view for strings escapes things that would normally be escaped in code. This means that things like inline quotes or real 's will be escaped with a \ (making quotes look like " and single slashes look like \).
These slashes are not in the actual string, they are only there in the text viewer. You can verify that by writing out the string to the console or the debug output. Your string.Replace didn't work because there was nothing to replace.
The actual string shows ok without double back slashes showing in the Console and in debugger using the magnifier , but when I add it to a List collection of strings it contains the double back slashes.
var data = new List<string>();
if (File.Exists(textFile))
{
// Read file using StreamReader. Reads file line by line
using (StreamReader file = new StreamReader(textFile))
{
string ln;
while ((ln = file.ReadLine()) != null)
{
Console.WriteLine(ln);
data.Add(ln); // <----- contains double quotes
}
file.Close();
}
}
the incoming file contains a lot of data from the mainframe.
I'm not expecting double quotes. I'm using VS 2017.

Write text to file in C# with 513 space characters

Here is a code that writes the string to a file
System.IO.File.WriteAllText("test.txt", "P ");
It's basically the character 'P' followed by a total of 513 space character.
When I open the file in Notepad++, it appears to be fine. However, when I open in windows Notepad, all I see is garbled characters.
If instead of 513 space character, I add 514 or 512, it opens fine in Notepad.
What am I missing?

What you are missing is that Notepad is guessing, and it is not because your length is specifically 513 spaces ... it is because it is an even number of bytes and the file size is >= 100 total bytes. Try 511 or 515 spaces ... or 99 ... you'll see the same misinterpretation of your file contents. With an odd number of bytes, Notepad can assume that your file is not any of the double-byte encodings, because those would all result in 2 bytes per character = even number of total bytes in the file. If you give the file a few more low-order ASCII characters at the beginning (e.g., "PICKLE" + spaces), Notepad does a much better job of understanding that it should treat the content as single-byte chars.
The suggested approach of including Encoding.UTF8 is the easiest fix ... it will write a BOM to the beginning of the file which tells Notepad (and Notepad++) what the format of the data is, so that it doesn't have to resort to this guessing behavior (you can see the difference between your original approach and the BOM approach by opening both in Notepad++, then look in the bottom-right corner of the app. With the BOM, it will tell you the encoding is UTF-8-BOM ... without it, it will just say UTF-8).
I should also say that the contents of your file are not 'wrong', per se... the weird format is purely due to Notepad's "guessing" algorithm. So unless it's a requirement that people use Notepad to read your file with 1 letter and a large, odd number of spaces ... maybe just don't sweat it. If you do change to writing the file with Encoding.UTF8, then you do need to ensure that any other system that reads your file knows how to honor the BOM, because it is a real change to the contents of your file. If you cannot verify that all consumers of your file can/will handle the BOM, then it may be safer to just understand that Notepad happens to make a bad guess for your specific use case, and leave the raw contents exactly how you want them.
You can verify the physical difference in your file with the BOM by doing a binary read and then converting them to a string (you can't "see" the change with ReadAllText, because it honors & strips the BOM):
byte[] contents = System.IO.File.ReadAllBytes("test.txt");
Console.WriteLine(Encoding.ASCII.GetString(contents));

Try passing in a different encoding:
i. System.IO.File.WriteAllText(filename , stringVariable, Encoding.UTF8);
ii. System.IO.File.WriteAllText(filename , stringVariable, Encoding.UTF32);
iii. etc.
Also You could try using another way to build your string, to make it be easier to read, change and count, instead of tapping the space bar 513 times;
i. Use the string constructor (like #Tigran suggested)
var result = "P" + new String(' ', 513);
ii. Use the stringBuilder
var stringBuilder = new StringBuilder();
stringBuilder.Append("P");
for (var i = 1; i <= 513; i++) { stringBuilder.Append(" "); }
iii. Or both
public string AppendSpacesToString(string stringValue, int numberOfSpaces)
{
var stringBuilder = new StringBuilder();
stringBuilder.Append(stringValue);
stringBuilder.Append(new String(' ', numberOfSpaces));
return stringBuilder.ToString();
}

C# Unrecognized characters while reading from binary file

I have some items who's information is split into two parts, one is contents of a binary file, and other is textual entry inside .txt file. I am trying to make an app that will pack this info into one textual file (textual file because I have reasons to want this file to also be humanly readable as well), with ability to later unpack that file back by creating new binary file and text entry.
The first problem I ran into so far: some info is lost when converting binary into string (or perhaps sooner, during reading of bytes), and I'm not sure if the file is in weird format or I'm doing something wrong. Some characters get shown as question marks.
Example of characters which are replaced with question marks:
ýÿÿ
This is the part where info is read from the binary file and gets encoded into a string (which is how I inteded to store it inside a text file).
byte[] binaryFile = File.ReadAllBytes(pathBinary);
// I also tried this for some reason: byte[] binaryFile = Encoding.ASCII.GetBytes(File.ReadAllText(pathBinary));
string binaryFileText = Convert.ToBase64String(binaryFile); //this is the coded string that goes into joined file to hold binary file information, when decoded the result shows question marks instead of some characters
MessageBox.Show("binary file text: " + Encoding.ASCII.GetString(binaryFile), "debug", MessageBoxButtons.OK, MessageBoxIcon.Information); //this also shows question marks
I expect a few more caveats along the way with second functionality of the app (unpacking back into text and binary), but so far my main problem is unrecognized characters during reading of the binary file or converting it into string, which makes this data unusable in storing as text for purpose of reproducing the file. Any help would be appreciated.

There is no universal conversion of binary string data to a string. A string is a series of unicode characters and as such can hold any character of the unicode range.
Binary data is a series of bytes and as such can be anything from video to a string in various formats.
Since there are multiple binary string representations, you need an Encoding to convert one into the other. The encoding you choose has to match the binary string format. If it doesn't you will get the wrong result.
You are using ASCII encoding for the conversion, which is obviously incorrect. ASCII can not encode the full unicode range. That means even if you use it for encoding, the result of the decoding will not always match the original text.
If you have both, encoding and decoding under control, use an Encoding that can do the full round trip, such as UTF8 or Unicode. If you don't encode the string yourself, use the correct Encoding.

Can not read turkish characters from text file to string array

I am trying to do some kind of sentence processing in turkish, and I am using text file for database. But I can not read turkish characters from text file, because of that I can not process the data correctly.
string[] Tempdatabase = File.ReadAllLines(#"C:\Users\dialogs.txt");
textBox1.Text = Tempdatabase[5];
Output:

It's probably an encoding issue. Try using one of the Turkish code page identifiers.
var Tempdatabase =
File.ReadAllLines(#"C:\Users\dialogs.txt", Encoding.GetEncoding("iso-8859-9"));

You can fiddle around using Encoding as much as you like. This might eventually yield the expected result, but bear in mind that this may not work with other files.
Usually, C# processes strings and files using Unicode by default. So unless you really need something else, you should try this instead:
Open your text file in notepad (or any other program) and save it as an UTF-8 file. Then, you should get the expected results without any modifications in your code. This is because C# reads the file using the encoding you saved it with. This is default behavior, which should be preferred.
When you save your text file as UTF-8, then C# will interpret it as such.
This also applies to .html files inside Visual Studio, if you notice that they are displayed incorrectly (parsed with ASCII)

The file contains the text in a specific Turkish character set, not Unicode. If you don't specify any other behaviour, .net will assume Unicode text when reading text from a text file. You have two possible solutions:
Either change the text file to use Unicode (for example utf8) using an external text editor.
Or specify a specific character set to read for example:
string[] Tempdatabase = File.ReadAllLines(#"C:\Users\dialogs.txt", Encoding.Default);
This will use the local character set of the Windows system.
string[] Tempdatabase = File.ReadAllLines(#"C:\Users\dialogs.txt", Encoding.GetEncoding("Windows-1254");
This will use the Turkish character set defined by Microsoft.

C# Reading files and encoding issue

I've searched everywhere for this answer so hopefully it's not a duplicate. I decided I'm just finally going to ask it here.
I have a file named Program1.exe When I drag that file into Notepad or Notepad++ I get all kinds of random symbols and then some readable text. However, when I try to read this file in C#, I either get inaccurate results, or just a big MZ. I've tried all supported encodings in C#. How can notepad programs read a file like this but I simply can't? I try to convert bytes to string and it doesn't work. I try to directly read line by line and it doesn't work. I've even tried binary and it doesn't work.
Thanks for the help! :)

Reading a binary file as text is a peculiar thing to do, but it is possible. Any of the 8-bit encodings will do it just fine. For example, the code below opens and reads an executable and outputs it to the console.
const string fname = #"C:\mystuff\program.exe";
using (var sw = new StreamReader(fname, Encoding.GetEncoding("windows-1252")))
{
var s = sw.ReadToEnd();
s = s.Replace('\x0', ' '); // replace NUL bytes with spaces
Console.WriteLine(s);
}
The result is very similar to what you'll see in Notepad or Notepad++. The "funny symbols" will differ based on how your console is configured, but you get the idea.
By the way, if you examine the string in the debugger, you're going to see something quite different. Those funny symbols are encoded as C# character escapes. For example, nul bytes (value 0) will display as \0 in the debugger, as NUL in Notepad++, and as spaces on the console or in Notepad. Newlines show up as \r in the debugger, etc.
As I said, reading a binary file as text is pretty peculiar. Unless you're just looking to see if there's human-readable data in the file, I can't imagine why you'd want to do this.
Update
I suspect the reason that all you see in the Windows Forms TextBox is "MZ" is that the Windows textbox control (which is what the TextBox ultimately uses), uses the NUL character as a string terminator, so won't display anything after the first NUL. And the first thing after the "MZ" is a NUL (shows as `\0' in the debugger). You'll have to replace the 0's in the string with spaces. I edited the code example above showing how you'd do that.

The exe is a binary file and if you try to read it as a text file you'll get the effect that you are describing. Try using something like a FileStream instead that does not care about the structure of the file but treats it just as a series of bytes.