I want to interpolation in the middle of a string, but I cannot use String.Format, because the string contains {} curly brackets.
This is what I have tried so far:
string code = "(function(){var myvariable = $"{variableToBeInterpolated}"});"
Returns: ) expected ; expected
Edit: I tried the following snippet, the interpolation is now working, but the code is not executed in the browser.
"(function(){var myvariable=" + $"{myvariable c#}" + ")});"
General Information
With C# version 6, extensive string interpolation capabilities have been added to the language.
String interpolation provides a more readable and convenient syntax to
create formatted strings than a string composite formatting feature.
To solve your problem, please have a look at the special characters section of the documentation, which reads the following:
To include a brace, "{" or "}", in the text produced by an
interpolated string, use two braces, "{{" or "}}".
Example
var variable = 10;
var code = $"(function() {{ var myVariable = {variable} }});";
Console.WriteLine(code);
Output: (function() { var myVariable = 10 });
Have you tried:
string someVariable = "test";
string code = $"(function()'{{var myvariable = ({someVariable} in c#)}});"
Using $ in C# is string interpolation. Added in C# 6
learn.microsoft.com
Why do you want to interpolate in the middle, rather put $ in front. And for { you need to use {{. (the same applies for })
string code = $"(function(){{ var myvariable = {myvariable} }});";
Related
the interpolated string is easy, just a string lead with $ sign. But what if the string template is coming from outside of your code. For example assume you have a XML file containing following line:
<filePath from="C:\data\settle{date}.csv" to="D:\data\settle{date}.csv"/>
Then you can use LINQ to XML read the content of the attributes in.
//assume the ele is the node <filePath></filePath>
string pathFrom = ele.Attribute("from").value;
string pathTo = ele.Attibute("to").value;
string date = DateTime.Today.ToString("MMddyyyy");
Now how can I inject the date into the pathFrom variable and pathTo variable?
If I have the control of the string itself, things are easy. I can just do var xxx=$"C:\data\settle{date}.csv";But now, what I have is only the variable that I know contains the placeholder date
String interpolation is a compiler feature, so it cannot be used at runtime. This should be clear from the fact that the names of the variables in the scope will in general not be availabe at runtime.
So you will have to roll your own replacement mechanism. It depends on your exact requirements what is best here.
If you only have one (or very few replacements), just do
output = input.Replace("{date}", date);
If the possible replacements are a long list, it might be better to use
output = Regex.Replace(input, #"\{\w+?\}",
match => GetValue(match.Value));
with
string GetValue(string variable)
{
switch (variable)
{
case "{date}":
return DateTime.Today.ToString("MMddyyyy");
default:
return "";
}
}
If you can get an IDictionary<string, string> mapping variable names to values you may simplify this to
output = Regex.Replace(input, #"\{\w+?\}",
match => replacements[match.Value.Substring(1, match.Value.Length-2)]);
You can't directly; the compiler turns your:
string world = "world";
var hw = $"Hello {world}"
Into something like:
string world = "world";
var hw = string.Format("Hello {0}", world);
(It chooses concat, format or formattablestring depending on the situation)
You could engage in a similar process yourself, by replacing "{date" with "{0" and putting the date as the second argument to a string format, etc.
SOLUTION 1:
If you have the ability to change something on xml template change {date} to {0}.
<filePath from="C:\data\settle{0}.csv" to="D:\data\settle{0}.csv" />
Then you can set the value of that like this.
var elementString = string.Format(element.ToString(), DateTime.Now.ToString("MMddyyyy"));
Output: <filePath from="C:\data\settle08092020.csv" to="D:\data\settle08092020.csv" />
SOLUTION 2:
If you can't change the xml template, then this might be my personal course to go.
<filePath from="C:\data\settle{date}.csv" to="D:\data\settle{date}.csv" />
Set the placeholder like this.
element.Attribute("to").Value = element.Attribute("to").Value.Replace("{date}", DateTime.Now.ToString("MMddyyyy"));
element.Attribute("from").Value = element.Attribute("from").Value.Replace("{date}", DateTime.Now.ToString("MMddyyyy"));
Output: <filePath from="C:\data\settle08092020.csv" to="D:\data\settle08092020.csv" />
I hope it helps. Kind regards.
If you treat your original string as a user-input string (or anything that is not processed by the compiler to replace the placeholder, then the question is simple - just use String.Replace() to replace the placehoder {date}, with the value of the date as you wish. Now the followup question is: are you sure that the compiler is not substituting it during compile time, and leaving it untouched for handling at the runtime?
String interpolation allows the developer to combine variables and text to form a string.
Example
Two int variables are created: foo and bar.
int foo = 34;
int bar = 42;
string resultString = $"The foo is {foo}, and the bar is {bar}.";
Console.WriteLine(resultString);
Output:
The foo is 34, and the bar is 42.
I can do this:
var log = string.Format("URL: {0}", url);
or even like this
var format = "URL: {0}";
...
var log = string.Format(format, url);
I have a format defined somewhere else and use the format variable, not inline string.
In C# 6, this is seems impossible:
var format = $"URL: {url}"; // Error url does not exist
...
var url = "http://google.com";
...
var log = $format; // The way to evaluate string interpolation here
Is there anyway to use string interpolation with variable declared earlier?
C# 6 seems interpolate the string inline during compile time. However consider using this feature for localization, define a format in config or simply having a format const in a class.
No, you can't use string interpolation with something other than a string literal as the compiler creates a "regular" format string even when you use string interpolation.
Because this:
string name = "bar";
string result = $"{name}";
is compiled into this:
string name = "bar";
string result = string.Format("{0}", name);
the string in runtime must be a "regular" format string and not the string interpolation equivalent.
You can use the plain old String.Format instead.
One approach to work around that would be to use a lambda containing the interpolated string. Something like:
Func<string, string> formatter = url => $"URL: {url}";
...
var googleUrl = "http://google.com";
...
var log = formatter(googleUrl);
In C# 7.0, you could use a local function instead of a lambda, to make the code slightly simpler and more efficient:
string formatter(string url) => $"URL: {url}";
...
var googleUrl = "http://google.com";
...
var log = formatter(googleUrl);
String interpolation is not library, but a compiler feature starting with C# 6.
The holes are not names, but expressions:
var r = new Rectangle(5, 4);
var s = $"Area: {r.Width * r.Heigh}":
How would you do that for localization, as you intend to?
Even r only exists at compile time. In IL it's just a position on the method's variable stack.
I've done what you intend to do for resources and configuration files.
Since you can only have a finite set of "variables" to substitute, what I did was have an array (or dictionary, if you prefer) and use a regular expression to replace the names in the holes with its index. What I did even allowed for format specifiers.
This is supposed to be a comment to the answer from i3arnon but I do not have the reputation :-( :
But for those who come to this old thread, in string.Format the format can be a variable:
string name = "bar";
string format = "{0}";
string result = string.Format(format, name);
works.
More of an idea as opposed to an answer.
For the example shown in the question, you can do the following.
var format = "URL: ";
...
var url = "http://google.com";
...
var result= $"{format} {url}";
I have an actual project where I have to do something like this a lot:
var label = "Some Label";
var value = "SomeValue";
//both label & value are results of some logic
var result = $"{label}: {value}";
You can with the right Nuget package: https://www.nuget.org/packages/InterpolatedStringFormatter
var mystring = "a thing(and something {other})";
Console.WriteLine(mystring.Interpolate("else"));
Outputs:
a thing(and something else)
It seems that you can do it like this:
var googleUrl = "http://google.com";
var url = $"URL: {googleUrl}";
System.Console.WriteLine(url);
You can check for more details in https://msdn.microsoft.com/en-us/library/dn961160.aspx
I can do this:
var log = string.Format("URL: {0}", url);
or even like this
var format = "URL: {0}";
...
var log = string.Format(format, url);
I have a format defined somewhere else and use the format variable, not inline string.
In C# 6, this is seems impossible:
var format = $"URL: {url}"; // Error url does not exist
...
var url = "http://google.com";
...
var log = $format; // The way to evaluate string interpolation here
Is there anyway to use string interpolation with variable declared earlier?
C# 6 seems interpolate the string inline during compile time. However consider using this feature for localization, define a format in config or simply having a format const in a class.
No, you can't use string interpolation with something other than a string literal as the compiler creates a "regular" format string even when you use string interpolation.
Because this:
string name = "bar";
string result = $"{name}";
is compiled into this:
string name = "bar";
string result = string.Format("{0}", name);
the string in runtime must be a "regular" format string and not the string interpolation equivalent.
You can use the plain old String.Format instead.
One approach to work around that would be to use a lambda containing the interpolated string. Something like:
Func<string, string> formatter = url => $"URL: {url}";
...
var googleUrl = "http://google.com";
...
var log = formatter(googleUrl);
In C# 7.0, you could use a local function instead of a lambda, to make the code slightly simpler and more efficient:
string formatter(string url) => $"URL: {url}";
...
var googleUrl = "http://google.com";
...
var log = formatter(googleUrl);
String interpolation is not library, but a compiler feature starting with C# 6.
The holes are not names, but expressions:
var r = new Rectangle(5, 4);
var s = $"Area: {r.Width * r.Heigh}":
How would you do that for localization, as you intend to?
Even r only exists at compile time. In IL it's just a position on the method's variable stack.
I've done what you intend to do for resources and configuration files.
Since you can only have a finite set of "variables" to substitute, what I did was have an array (or dictionary, if you prefer) and use a regular expression to replace the names in the holes with its index. What I did even allowed for format specifiers.
This is supposed to be a comment to the answer from i3arnon but I do not have the reputation :-( :
But for those who come to this old thread, in string.Format the format can be a variable:
string name = "bar";
string format = "{0}";
string result = string.Format(format, name);
works.
More of an idea as opposed to an answer.
For the example shown in the question, you can do the following.
var format = "URL: ";
...
var url = "http://google.com";
...
var result= $"{format} {url}";
I have an actual project where I have to do something like this a lot:
var label = "Some Label";
var value = "SomeValue";
//both label & value are results of some logic
var result = $"{label}: {value}";
You can with the right Nuget package: https://www.nuget.org/packages/InterpolatedStringFormatter
var mystring = "a thing(and something {other})";
Console.WriteLine(mystring.Interpolate("else"));
Outputs:
a thing(and something else)
It seems that you can do it like this:
var googleUrl = "http://google.com";
var url = $"URL: {googleUrl}";
System.Console.WriteLine(url);
You can check for more details in https://msdn.microsoft.com/en-us/library/dn961160.aspx
Hi all I want to know something regarding to fixed-string in regular expression.
How to represent a fixed-string, regardless of special characters or alphanumeric in C#?
For eg; have a look at the following string:
infinity.world.uk/Members/namelist.aspx?ID=-1&fid=X
The entire string before X will be fixed-string (ie; the whole sentence will appear the same) BUT only X will be the decimal variable.
What I want is that I want to append decimal number X to the fixed string. How to express that in terms of C# regular expression.
Appreciate your help
string fulltext = "inifinity.world.uk/Members/namelist.aspx?ID=-1&fid=" + 10;
if you need to modify existing url, dont use regex, string.Format or string.Replace you get problem with encoding of arguments
Use Uri and HttpUtility instead:
var url = new Uri("http://infinity.world.uk/Members/namelist.aspx?ID=-1&fid=X");
var query = HttpUtility.ParseQueryString(url.Query);
query["fid"] = 10.ToString();
var newUrl = url.GetLeftPart(UriPartial.Path) + "?" + query;
result: http://infinity.world.uk/Members/namelist.aspx?ID=-1&fid=10
for example, using query["fid"] = "%".ToString(); you correctly generate http://infinity.world.uk/Members/namelist.aspx?ID=-1&fid=%25
demo: https://dotnetfiddle.net/zZ9Y1h
String.Format is one way of replacing token values in a string, if that's what you want. In the example below, the {0} is a token, and String.Format takes the fixedString and replaces the token with the value of myDecimal.
string fixedString = "infinity.world.uk/Members/namelist.aspx?ID=-1&fid={0}";
decimal myDecimal = 1.5d;
string myResultString = string.Format(fixedString, myDecimal.ToString());
If I write something like this:
string s = #"...."......";
it doesn't work.
If I try this:
string s = #"...\".....";
it doesn't work either.
How can I add a " character to a multi line string declaration in C#?
Try this:
string s = #"..."".....";
The double character usage also works with the characters { and } when you're using string.Format and you want to include a literal instance of either rather than indicate a parameter argument, for example:
string jsString = string.Format(
"var jsonUrls = {{firstUrl: '{0}', secondUrl: '{1}'}};",
firstUrl,
secondUrl
);
string s = "...\"....."; should work
the # disables escapes so if you want to use \" then no # symbol
Personally i think you should go with
string s = string.format("{0}\"{1},"something","something else");
it makes it easier in the long run