How do I escape with the #-sign when using variables?
File.Delete(#"c:\test"); // WORKS!
File.Delete(#path); // doesn't work :(
File.Delete(#"c:\test"+path); // WORKS
Anyone have any idea? It's the 2nd example I want to use!
Strings prefixed with # character are called verbatim string literals (whose contents do not need to be escaped).
Therefore, you can only use # with string literals, not string variables.
So, just File.Delete(path); will do, after you assign the path in advance of course (from a verbatim string or some other string).
Verbatim strings are just a syntactic nicety to be able to type strings containing backslashes (paths, regexes) easier. The declarations
string path = "C:\\test";
string path = #"C:\test";
are completely identical in their result. Both result in a string containing C:\test. Note that either option is just needed because the C# language treats \ in strings as special.
The # is not some magic pixie dust needed to make paths work properly, it has a defined meaning when prefixed to strings, in that the strings are interpreted without the usual \ escape sequences.
The reason your second example doesn't work like you expect is that # prefixed to a variable name does something different: It allows you to use reserved keywords as identifiers, so that you could use #class as an identifier, for example. For identifiers that don't clash with keywords the result is the same as without.
If you have a string variable containing a path, then you can usually assume that there is no escaping needed at all. After all it already is in a string. The things I mentioned above are needed to get text from source code correctly through the compiler into a string at runtime, because the compiler has different ideas. The string itself is just data that's always represented the same.
This still means that you have to initialise the string in a way that backslashes survive. If you read it from somewhere no special treatment should be necessary, if you have it as a constant string somewhere else in the code, then again, one of the options at the top has to be used.
string path = #"c:\test";
File.Delete(path);
This will work only on a string. The "real" string is "c:\\test".
Read more here.
There's a major problem with your understanding of the # indicator.
#"whatever string" is a literal string specifier verbatim string literal. What it does is tells the C# compiler to not look for escape sequences. Normally, "\" is an escape sequence in a string, and you can do things like "\n" to indicate a new line or "\t" to indicate a tab. However, if you have #"\n", it tells the compiler "no, I really want to treat the backslash as a backslash character, not an escape sequence."
If you don't like literal mode, the way to do it is to use "\\" anywhere you want a single backslash, because the compiler knows to treat an escaped backslash as the single character.
In either case, #"\n" and "\\n" will produce a 2-character string in memory, with the characters '\' and 'n'. It doesn't matter which way you get there; both are ways of telling the compiler you want those two characters.
In light of this, #path makes no sense, because you don't have any literal characters - just a variable. By the time you have the variable, you already have the characters you want in memory. It does compile ok, as explained by Joey, but it's not logically what you're looking for.
If you're looking for a way to get rid of occurrences of \\ within a variable, you simply want String.Replace:
string ugly = #"C:\\foo";
ugly = ugly.Replace(#"\\", #"\");
First and third are actual paths hence would work.
Second would not even compile and would work if
string path = #"c:\test";
File.Delete(path);
Related
Perhaps I didn't see or understand any of the answers I read but I am having trouble using verbatim string literal (#) with settings.Default.(mysetting). I am trying to do something like
Directory.GetFiles(#Setting.Default.(mysetting),"*.txt");
and cant seem to find the right syntax to make this work.
The # identifies a string constant literal where back slashes should not be interpreted as escape signs. You can not use it in front of method invocations as you attempt here.
A valid assignment might be
string path = #"c:\temp\example.txt";
Usually a \t would be interpreted as a tabulation character thus making the file reference illegal. It is exactly identical to
string path = "c:\\temp\\example.txt" ;
But bit easier to read.
# verbatim string is used with string literals. So your code should be:
Directory.GetFiles(Setting.Default.(mysetting),#"*.txt");
because "*.txt" is the string literal in your code.
(Although not related, but you can use # with variable names see C# Variable Naming and the # Symbol)
To use # as part of a verbatim string literal, the string literal must be right there - not just a property, method, etc. that returns a string.
string myStr = #"I'm verbatim, I contain a literal \n";
string myStr2 = "I'm not\nI have a newline";
string myStr3 = #myStr2; // still contains a newline, not a literal "\n"
Using # in front of an identifier allows you to use reserved keywords as identifiers. For example:
string #if = "hello!"; // valid
It also works on non-reserved words, where it has no real effect.
string #myVar = "hello!"; // valid
string newVar = myVar; // can be referred to either way
Unless I'm missing it, you still need to wrap the string within quotation marks.
I want to write something like this C:\Users\UserName\Documents\Tasks in a textbox:
txtPath.Text = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)+"\Tasks";
I get the error:
Unrecognized escape sequence.
How do I write a backslash in a string?
The backslash ("\") character is a special escape character used to indicate other special characters such as new lines (\n), tabs (\t), or quotation marks (\").
If you want to include a backslash character itself, you need two backslashes or use the # verbatim string:
var s = "\\Tasks";
// or
var s = #"\Tasks";
Read the MSDN documentation/C# Specification which discusses the characters that are escaped using the backslash character and the use of the verbatim string literal.
Generally speaking, most C# .NET developers tend to favour using the # verbatim strings when building file/folder paths since it saves them from having to write double backslashes all the time and they can directly copy/paste the path, so I would suggest that you get in the habit of doing the same.
That all said, in this case, I would actually recommend you use the Path.Combine utility method as in #lordkain's answer as then you don't need to worry about whether backslashes are already included in the paths and accidentally doubling-up the slashes or omitting them altogether when combining parts of paths.
To escape the backslash, simply use 2 of them, like this:
\\
If you need to escape other things, this may be helpful..
There is a special function made for this Path.Combine()
var folder = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
var fullpath = path.Combine(folder,"Tasks");
Just escape the "\" by using + "\\Tasks" or use a verbatim string like #"\Tasks"
txtPath.Text = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)+"\\\Tasks";
Put a double backslash instead of a single backslash...
even though this post is quite old I tried something that worked for my case .
I wanted to create a string variable with the value below:
21541_12_1_13\":null
so my approach was like that:
build the string using verbatim
string substring = #"21541_12_1_13\"":null";
and then remove the unwanted backslashes using Remove function
string newsubstring = substring.Remove(13, 1);
Hope that helps.
Cheers
Is there any difference in how the C# compiler or .NET run-time handles verbatim string literals versus using escape sequences (i.e. performance) or is it just a matter of design time style? E.G.:
var pathA = "c:\\somewhere";
var pathB = #"c:\somewhere";
I would imagine they are compiled the same and it doesn't matter, but was just curious.
Any difference here is limited strictly to the compiler; the IL and runtime have no concept of verbatim vs escaped - it just has the string.
As for which to choose: whichever is more convenient ;p I almost always use verbatim string literals if there are unusual characters, as that allows for multi-line strings very easily and visually.
As an interesting case:
bool areSame = ReferenceEquals("c:\\somewhere", #"c:\somewhere"); // true
which tells are they are exactly the same string instance (thanks to "interning"). They aren't just equivalent; they are the same string instance to the runtime. It is therefore impossible that they can be (to the runtime) different in any way.
They are exactly the same. Try to decompile the two versions with a decompiler.
It's only a matter of convenience for developers when writing it in the code.
The # sign in front of a string tells the compiler to ignore any embeded
escape sequences.
string "\"" would yield a single double quote.
string "\" would yield a single back slash
string #"\" would yield two backslashes
I am using .NET (C#) code to write to a database that interfaces with a Perl application. When a single quote appears in a string, I need to "escape" it. IOW, the name O'Bannon should convert to O\'Bannon for the database UPDATE. However, all efforts at string manipulation (e.g. .Replace) generate an escape character for the backslash and I end up with O\\'Bannon.
I know it is actually generating the second backslash, because I can read the resulting database field's value (i.e. it is not just the IDE debug value for the string).
How can I get just the single backslash in the output string?
R
Well I did
"O'Bannon".Replace("'","\\'")
and result is
"O\'Bannon"
Is this what you want?
You can use "\\", which is the escape char followed by a backslash.
See the list of Escape Sequences here: http://msdn.microsoft.com/en-us/library/h21280bw.aspx
even better assign a var to the replace so that you can check it as well if needed
var RepName = "O'Bannon";
var Repstr = RepName.Replace("'","\\'");
You can also use a verbatim string
s = s.Replace("'", #"\'");
I have a helper class pulling a string from an XML file. That string is a file path (so it has backslashes in it). I need to use that string as it is... How can I use it like I would with the literal command?
Instead of this:
string filePath = #"C:\somepath\file.txt";
I want to do this:
string filePath = #helper.getFilePath(); //getFilePath returns a string
This isn't how I am actually using it; it is just to make what I mean a little clearer. Is there some sort of .ToLiteral() or something?
I don't think you have to worry about it if you already have the value. The # operator is for when you're specifying the string (like in your first code snippet).
What are you attempting to do with the path string that isn't working?
I'm not sure if I understand. In your example: if helper.getFilePath() returns "c:\somepath\file.txt", there will be no problem, since the # is only needed if you are explicitely specifying a string with "".
When Functions talk to each other, you will always get the literal path. If the XML contains c:\somepath\file.txt and your function returns c:\somepath\file.txt, then string filePath will also contain c:\somepath\file.txt as a valid path.
The #"" just makes it easier to write string literals.
string (C# Reference, MSDN)
Verbatim string literals start with # and are also enclosed in double quotation marks. For example:
#"good morning" // a string literal
The advantage of verbatim strings is that escape sequences are not processed, which makes it easy to write, for example, a fully qualified file name:
#"c:\Docs\Source\a.txt" // rather than "c:\\Docs\\Source\\a.txt"
One place where I've used it is in a regex pattern:
string pattern = #"\b[DdFf][0-9]+\b";
If you have a string in a variable, you do not need to make a "literal" out of it, since if it is well formed, it already has the correct contents.
In C# the # symbol combined with doubles quotes allows you to write escaped strings. E.g.
print(#"c:\mydir\dont\have\to\escape\backslashes\etc");
If you dont use it then you need to use the escape character in your strings.
http://msdn.microsoft.com/en-us/library/aa691090(VS.71).aspx
You dont need to specify it anywhere else in code. In fact doing so should cause a compiler error.
You've got it backwards. The #-operator is for turning literals into strings, while keeping all funky characters. Your path is already a string - you don't need to do anything at all to it. Just lose the #.
string filePath = helper.getFilePath();
The string returned from your helper class is not a literal string so you don't need to use the '#' character to remove the behaviour of the backslashes.