var a = "asdfgh\r";
Console.WriteLine(a.Contains(#"\r"));
var b = a.Replace(#"\r","").Replace(#"\n","");
var c = a.Replace("\r","").Replace("\n","");
Console.WriteLine(a);
Console.WriteLine(b);
Console.WriteLine(c);
"b" and "c" prints same string and "a" prints false,
I was trying to replace \r and \n to an empty char so first i tried below code, there's a backslash in "\r" and "\n" so i decided to use "#" before them ;
var b = a.Replace(#"\r","").Replace(#"\n","")
but this didn't work,
var c = a.Replace("\r","").Replace("\n","");
this works, so im confused when should i use "#" charachter ?
You declared string a to end with carriagereturn character:
var a = "asdfgh\r"; //it has a length of 7 when compiled
So you must replace the carriage return with nothing:
Replace("\r","")
If you had declared the string to end with "backslash r":
var a = #"asdfgh\r"; //it has a length of 8 when compiled
Then you would have succeeded in replacing "backslash r" with nothing:
Replace(#"\r","")
This would also work:
Replace("\\r","")
Because the double slash is turned into a single and then the r is a normal character so you're replacing "backslash r" and not carriagereturn
When compiling the C# compiler looks for \ in a string and converts the following character(s) according to some rule. Using # before the string turns this off. Mostly it's useful for paths. Remember that it's a compile time thing, not something you need to do to variables that hold data entered in runtime. Putting an # before a variable name means something different - allowing you to call a variable a reserved word, like string #for = "for" - deplorable practice; don't do it
Ultimately the problem is that you were inconsistent when declaring your strings - a was not a verbatim string so it really did have a single carriage return char, and then you were trying to replace using a verbatim string (and "backslash r" is a different string to "carriagereturn"
Related
I have this pattern to validate that if a string is correct or not.
public string isStringConstant(string vPart)
{
string pattern = #"^\""[\\(t|r|n|0|b|f|""|a|v|')a-zA-Z0-9,\.\*/;\~!\{\}##\$%\^:&\(\)\+\[\]<>_\?=\-`]*\""$";
Regex obj = new Regex(pattern);
if (obj.IsMatch(vPart))
{
return "StringConstant";
}
return "INVALID";
}
It works well but it also validates the following string which it should not.
"harisnabeel\"
The input string source is a text file.
What wrong I am doing with that pattern?
Look at this part: \\(t|r|n|0|b|f|""|a|v|')
You are trying to shortcut having to write out \t\r\n, etc. In the process you have \, which says \ is a valid character in your string. Rewrite your "or this or that" portion long hand and you should be fine. Don't have time to test this personally, but a bit of experimentation with that will solve your problem.
If we follow the title (Regex to validate String like C# does), the full regex should be:
// https://learn.microsoft.com/it-it/dotnet/csharp/language-reference/language-specification/lexical-structure#string-literals
// A character that follows a backslash character (\) in
// a regular_string_literal_character must be one of the following
// characters: ', ", \, 0, a, b, f, n, r, t, u, U, x, v.
// Otherwise, a compile-time error occurs.
var rx = new Regex(#"^""(\\(?:['""\\0abfnrtv]|u[0-9A-Fa-f]{4}|U[0-9A-Fa-f]{8}|x[0-9A-Fa-f]{1,4})|[^\\""]+)*""$");
All the "" are double, because the regex is based on a string-literal (#"..."), so they became a single " each.
Note the ending [^\\""] that becomes [^\\"] because the string is a literal string, so any character that isn't an escape \ or a " (the \ is handled separately, the unescaped " is the ending of the string). Note even the doubling of the \\, because otherwise a single \ becomes an escape sequence of the regex, and the handling of \x, \u and \U.
Example of use:
var res = rx.Match(#"""Hello\nWorld\\\""\x123G""");
The "pieces" of the string:
var pieces = res.Groups[1].Captures.Cast<Capture>().ToArray();
In this case Hello, \n, World, \x123, G
I am trying to replace \" in a string with ", how may i do that?
I've tried using replace but i could not find a way to do it.
Ex:
string line = "This is a \"sample\" "
string replaced = "This is a "sample" ".
Thanks.
Because quotes are used to start and end strings (they are a type of control character), you can't have a quote in the middle of a string because it would terminate the string
string replaced = "This is a "sample" ";
/*
You can see from the syntax highlighting (red) that the string is being
detected as <This is a > and <sample> is black meaning it is detected as
code (and will cause a syntax error)
*/
In order to put a quote in the middle of the string we escape it (escaping means to treat it as a character literal instead of a control character) using the escape character, which in C# is backslash.
string line = "This is a \"sample\"";
Console.WriteLine(line);
// Output: This is a "sample"
string literalLine = #"This is a ""sample""";
Console.WriteLine(literalLine);
// Output: This is a "sample"
The # symbol in C# means I want this to be a literal string (ignore control characters), however quotes still start and end strings so in order to print a quote in a literal string you write two of them "" (that's how the language is designed)
Case 1: If the value within the variable line is actually This is a \"sample\", then you could do line.Replace("\\\"", "\"").
If not:
\" is an escape sequence. it shows up as \" in the code, however when it compiles it would show up as " instead of the original \".
The reason for escaping quotes is because the compiler cannot identify whether the quote is within another quote or not. Let's see your example:
"This is a "sample" "
is this This is a as one group, then an unknown token sample, then another quote ? or This is a "sample" all within a quote? We can take a guess by looking at the context, but compiler cannot. Hence, we use escape sequence to tell the compiler "I used this double quote character as a character, not the closing/opening of a string literal."
See Also: https://en.wikipedia.org/wiki/Escape_sequences_in_C
You may try something like this:
String str = "This is a \"sample\" ";
Console.WriteLine("Original string: {0}", str);
Console.WriteLine("Replaced: {0}", str.Replace('\"', '"'));
Desired output : This is a sample
Given string : "This is a \"sample\""
The problem: you have escape characters protecting the double quotes from being interpreted. the \ escape character is an instruction to use a quotation mark literally instead of using it to indicate a break in the string. This means the actual string value is "This is a "sample"" when served as output.
The answer removing the \ may work, but it makes for smelly code because removing an escape character in this way can make it unclear what you intend and prevents you from escaping any character.
Removing the " might work, though it prevents use of any quotes and some IDEs might leave the escape character behind to ruin your day.
We want one specific target, the quotes around "sample".
string sample = "This is a \"sample\"";
List<string> sampleArray = sample.Split(' ').ToList(); // samplearray is now split into ["This", "is", "a", "\"sample\""]
var x = sampleArray.FirstOrDefault(t => t == "\"sample\""); //isolate our needed value
if (x != null) //prevent a null reference in case something went wrong and samplearray wasnt as expected
{
var index = sampleArray.IndexOf(x); //get the location of the value we just picked
x = x.Replace("\"", string.Empty); //replace chars
sampleArray[index] = x; //assign new value to the list
}
return String.Join(" ", sampleArray); //return the string joined together with spaces.
Try this:
string line="This is a \"sample\" " ;
replaced =line.Replace(#"\", "");
string s = "P\04";
string z = s.Replace('\\', '-');
Console.WriteLine(z);
I need to replace '\' character in to '-' character in a string. I tried several ways to replace, couldn't able to do for '\' character only.
Please any one suggest a way to do this
Your code to replace the \ is fine. The problem is with your input string, where the \ escapes the 0. It would work if you had this:
string s = "P\\04";
string z = s.Replace('\\', '-');
Console.WriteLine(z);
The output is P-04 assuming that's what you expect.
string s = #"P\04";
string z = s.Replace('\\', '-');
Console.WriteLine(z);
Add # at the before value of string s to make it a verbatim. That way '\' is treated as is. Otherwise \0 are treated as one character to make a different character.
You can also use Regex,
var result = Regex.Replace(#"P\04", #"\\", #"-");
Console.WriteLine(result);
FIDDLE
I have a long string (a path) with double backslashes, and I want to replace it with single backslashes:
string a = "a\\b\\c\\d";
string b = a.Replace(#"\\", #"\");
This code does nothing...
b remains "a\\b\\c\\d"
I also tried different combinations of backslashes instead of using #, but no luck.
Because you declared a without using #, the string a does not contain any double-slashes in your example. In fact, in your example, a == "a\b\c\d", so Replace does not find anything to replace. Try:
string a = #"a\\b\\c\\d";
string b = a.Replace(#"\\", #"\");
In C#, you can't have a string like "a\b\c\d", because the \ has a special meaning: it creates a escape sequence together with a following letter (or combination of digits).
\b represents actually a backspace, and \c and \d are invalid escape sequences (the compiler will complain about an "Unrecognized escape sequence").
So how do you create a string with a simple \? You have to use a backslash to espace the backslash:\\ (it's the espace sequence that represents a single backslash).
That means that the string "a\\b\\c\\d" actually represents a\b\c\d (it doesn't represent a\\b\\c\\d, so no double backslashes). You'll see it yourself if you try to print this string.
C# also has a feature called verbatim string literals (strings that start with #), which allows you to write #"a\b\c\d" instead of "a\\b\\c\\d".
You're wrong. "\\" return \ (know as escaping)
string a = "a\\b\\c\\d";
System.Console.WriteLine(a); // prints a\b\c\d
string b = a.Replace(#"\\", #"\");
System.Console.WriteLine(b); // prints a\b\c\d
You don't even need string b = a.Replace(#"\\", #"\");
this works
You don't even need string b = a.Replace(#"\", #"\");
but like if we generate a dos command through c# code... eg:- to delete a file
this wil help
I did this in a code in a UWP application.
foreach (var item in Attendances)
{
string a = item.ImagePath;
string b = a.Replace(#"\\", "/");
string c = a.Replace("\\", "/");
Console.WriteLine(b);
Console.WriteLine(a);
item.ImagePath = c;
}
and the ones without the # symbol is the one that actually worked. this is C# 8 and C# 9
Using C# we can do string check like if string.contains() method, e.g.:
string test = "Microsoft";
if (test.Contains("i"))
test = test.Replace("i","a");
This is fine. But what if I want to replace a string which contains " symbol to be replaced.
I want to achieve this:
"<html><head>
I want to remove the " symbol present in check so that the result would be:
<html><head>
The " character can also be replaced, just like any other:
test = test.Replace("\"","");
Also, note that you don't have to test if the character exists : your test.Contains("i") could be removed since the .Replace() method won't do anything (no replace, no error thrown) if the character doesn't exist inside the string.
To include a quote symbol in a string, you need to escape it, using a backslash. In your example, you want to use something lik this:
if (test.Contains("\""))
There are two ways to include a '"' character in a string literal. All the answers so far have used the c-style way:
var quotation = "Parting is such sweet sorrow";
var howSweetIsIt = quotation + " that I shall say \"good-night\" till it be morrow.";
In some contexts (especially for users experienced with Visual Basic), the verbatim string literal may be easier to read. A verbatim string literal begins with an # sign, and the only character that requires escaping is the quotation mark -- all other characters are included verbatim (hence the name). Significantly, the method of escaping the quotation mark is different: rather than preceding it with a backslash, it must be doubled:
var howSweetIsIt = quotation + " that I shall say ""good-night"" till it be morrow.";
string SymbolString = "Micro\"so\"ft";
The string above use scape char \ to insert " between the characters
string Result = SymbolString.Replace("\"", string.Empty);
With the following replace I replace the character "" for empty.
This is what you try to achieve?
if (check.Contains("\"")
output = check.Replace("\"", "");
output = check.Replace("\"", "");
Just remember to use "\"" for the quote sign as the backslash is an escape character.
if (str.Contains("\""))
{
str = str.Replace("\"", "");
}