What is the difference between the \ and the / when doing streamwriter?
e.g.
Example 1:
Streamwriter sw = new Streamwriter("/test folder/Output/test.txt");
and
Example 2:
Streamwriter sw = new Streamwriter(#"\test folder\Output\test.txt");
I see you need the # symbol in the front on the second example too.
There is no difference because .NET recognizes both one and the other in paths.
However, since \ has special meaning when appearing inside a string literal (it is the beginning of an escape sequence) the second example uses verbatim string literal syntax. It could have used \\ in place of \ instead.
Adding # only improves readability, a string starting with # will simply have all its \'s replaced by \\ during compile time and \ added where needed.
Both are valid path separator characters in .NET.
IOW, it is exactly the same thing.
The \ is generally used in Windows to separate directories, however I think it does accept / in most circumstances as well.
The \ also needs to be escaped, hence the # symbol. You could also use \\ to escape this character as well.
Because with \ start escape characters. For example "\"" will print ". If you want to use \ as a character either you need to add # in front of string or use \\. As you see it has nothing to do with path-s both form are valid for streamwriter.
Related
I am trying to replace a string using regex, however I can't seem to find a way to escape the single backslashes for the regex with the double backslashes of the string.
My string literal (this is being read from a text file, as is)
-s \"t\"
and I want to replace it with (again, as a string literal)
-s \"n\"
The best I have been able to come up with is
schedule = Regex.Replace(schedule, "-s\s\\\"\w\\\"", "-s \\\"n\\\"");
The middle argument doesn't compile though, because of the single and double backslashes. It will accept one or the other, but not both (regardless of weather I use #).
I don't use regexes that much so it may be a simple one but I'm pretty stuck!
Thanks
The problem is happening because \ have a special meaning both for strings and regular expressions so it normally needs to be double escaped unless you use # and added to the problem here is the presence of " itself inside the string which needs to be escaped.
Try the following:
schedule = Regex.Replace(schedule, #"-s\s\\""\w\\""", #"-s \""n\""");
After using #, \ doesn't have a special meaning inside strings, but it still have a special meaning inside regular expression expression so it needs to be escaped only once if it is needed literally.
Also now you need to use "" to escape " inside the string (how would you escape it otherwise, since \ doesn't have a special meaning anymore).
This works:
var schedule = #"-s \""t\""";
// value is -s \"t\"
schedule = Regex.Replace(schedule, #"-s\s\\""\w\\""", #"-s \""n\""");
// value is -s \"n\"
The escaping is complicated because \ and " have special meanings both in how you encode strings in C# and in regex. The search pattern is (without any escaping) the C# string -s\s\\"\w\\", which tells regex to look for a literal \ and a literal ". The replacement string is -s \"n\", because you don't need to escape the backslashes in a replacement string.
You could, of course, write this with normal strings ("...") instead of verbatim strings (#"..."), but it'd get way messier.
I have stringBuilder & string class, storing a path:
StringBuilder name = new StringBuilder();
name.Append(#"NETWORK\MyComputer");
String serverName = name.ToString(); //this converts the \ to a \\
I have tried a number of things, but it always results in the string having \
Using serverName.Replace("\\", #"\"); doesn't work, it leaves it as a \
servername.Replace("\\", "\""); adds a " to the string, which is still not correct.
Please assist.
If you are concerned at a single back slash being shown as a double back slash then don't be - that is simply the way it is shown to you in the debugger.
The back slash is a special character, that 'specialness' is turned off by doubling it up. Alternatively the # symbol can be prefixed to the string in source code which avoids having to use it.
Use
name.Append(Path.Combine("NETWORK", "MyComputer");
In strings \ is an escape sequence. So \ in debugger will be \\
Acc.to MSDN
Character combinations consisting of a backslash (\) followed by a letter or by a combination of digits are called "escape sequences." To represent a newline character, single quotation mark, or certain other characters in a character constant, you must use escape sequences. An escape sequence is regarded as a single character and is therefore valid as a character constant.
Escape sequences are typically used to specify actions such as carriage returns and tab movements on terminals and printers. They are also used to provide literal representations of nonprinting characters and characters that usually have special meanings, such as the double quotation mark ("). The following table lists the ANSI escape sequences and what they represent.
Read Escape Sequences
I don't think your code can be compiled. Because \ is an escape character, thus the string "\" will be wrong. The #"\" is right because the # (literal) has ignored that escape and tread it as a normal character.
See more here
I've noticed that C# adds additional slashes (\) to paths. Consider the path C:\Test. When I inspect the string with this path in the text visualiser, the actual string is C:\\Test.
Why is this? It confuses me, as sometimes I may want to split the path up (using string.Split()), but have to wonder which string to use (one or two slashes).
The \\ is used because the \ is an escape character and is need to represent the a single \.
So it is saying treat the first \ as an escape character and then the second \ is taken as the actual value. If not the next character after the first \ would be parsed as an escaped character.
Here is a list of available escape characters:
\' - single quote, needed for character literals
\" - double quote, needed for string literals
\\ - backslash
\0 – Null
\a - Alert
\b - Backspace
\f - Form feed
\n - New line
\r - Carriage return
\t - Horizontal tab
\v - Vertical quote
\u - Unicode escape sequence for character
\U - Unicode escape sequence for surrogate pairs.
\x - Unicode escape sequence similar to "\u" except with variable length.
EDIT: To answer your question regarding Split, it should be no issue. Use Split as you would normally. The \\ will be treated as only the one character of \.
.Net is not adding anything to your string here. What your seeing is an effect of how the debugger chooses to display strings. C# strings can be represented in 2 forms
Verbatim Strings: Prefixed with an # sign and removes the need o escape \\ characters
Normal Strings: Standard C style strings where \\ characters need to escape themselves
The debugger will display a string literal as a normal string vs. a verbatim string. It's just an issue of display though, it doesn't affect it's underlying value.
Debugger visualizers display strings in the form in which they would appear in C# code. Since \ is used to escape characters in non-verbatum C# strings, \\ is the correct escaped form.
Okay, so the answers above are not wholly correct. As such I am adding my findings for the next person who reads this post.
You cannot split a string using any of the chars in the table above if you are reading said string(s) from an external source.
i.e,
string[] splitStrings = File.ReadAllText([path]).Split((char)7);
will not split by those chars. However internally created strings work fine.
i.e.,
string[] splitStrings = "hello\agoodbye".Split((char)7);
This may not hold true for other methods of reading text from a file. I am unsure as I have not tested with other methods. With that in mind, it is probably best not to use those chars for delimiting strings!
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Closed 11 years ago.
Possible Duplicate:
What's the # in front of a string for .NET?
I have the following code:
new Attachment(Request.PhysicalApplicationPath + #"pdf\" + pdfItem.Value)
What does the # sign do?
It has nothing to do with filepath. It changes the escaping behavior of strings.
In a string literal prefixed with # the escape sequences starting with \ are disabled. This is convenient for filepaths since \ is the path separator and you don't want it to start an escape sequence.
In a normal string you would have to escape \ into \\ so your example would look like this "pdf\\". But since it's prefixed with # the only character that needs escaping is " (which is escaped as "") and the \ can simply appear.
This feature is convenient for strings literals containing \ such as filepaths or regexes.
For your simple example the gain isn't that big, but image you have a full path "C:\\ABC\\CDE\\DEF" then #"C:\ABC\CDE\DEF" looks a lot nicer.
For regular expressions it's almost a must. A regex typically contains several \ escaping other characters already and often becomes almost unreadable if you need to escape them.
It's a verbatim string literal.
This allows the string to contain backslashes and even linebreaks without them being handled differently:
string multiLineString = #"First line
second line
third line";
As backslashes aren't used for escaping, inserting a double quote into the string requires it to be doubled:
string withQuote = #"before""after";
Verbatim string literals are typically used for file paths (as you've shown) and regular expressions, both of which frequently use backslashes.
See my article on strings for more information.
It allows you to enter the backslash (\) without escaping it:
var s1 = "C:\\Temp\\MyFileName";
var s2 = #"C:\Temp\MyFileName";
Both result in a string with the same contents (and since strings are interned at compile time, probably even the same string reference).
How can I replace the "\" in a string with a double slash "\\"?
I tried String.Replace("\","\\") but then intellisense stops working :(
Thanks!
Try:
String.Replace("\\","\\\\")
This is because a character can follow \, which makes a special character. \" means put a literal double quote in the string, rather than close it.
Here are some common ones:
\n - Line feed
\r - Carriage return (Windows newlines are \r\n)
\t - Tab
The other answers, which say to use #"\" are right and easier to understand, so should probably be used instead.
\ is a reserved character in a string, it's an "escape". So, for instance, \n means a linefeed constant.
string.Replace(#"\", #"\\") would work just fine -- the # tells the compiler to ignore the escaping of \.
Alternatively, \\ means one backslash -- so string.Replace("\\", "\\\\") would work just fine too (although it's a bit unreadable).
Use '#' to make backslash lose its special meaning:
String.Replace(#"\", #"\\")