I'm beginer in C#. Now I have next task: In method I get template and arguments and I have to return formated string.
For example:
template = "Hello, {name}!"
name = "Bob"
So result must be a string -> Hello, Bob!
public static string GetHelloGreeting(string template, string name)
{
return string.Format(template, name);
}
String.Format expects an index in the braces. You want to pass the name in it, so you can replace it with the actual name value.
I'd suggest to use String.Replace:
public static string GetHelloGreeting(string template, string name)
{
return template.Replace("{name}", name);
}
You could provide a method which is more reusable. For example:
public static string ReplaceAll(string template, params (string key, string value)[] replacements)
{
foreach (var kv in replacements)
{
template = template.Replace("{"+ kv.key + "}", kv.value);
}
return template;
}
Your example:
string res = ReplaceAll("Hello, {name}!", ("name", "Bob"));
but also possible with multiple parameters:
string res = ReplaceAll("Hello, {name}! Now it's {time}", ("name", "Bob"), ("time", DateTime.Now.ToString("HH:mm")));
The value of your template parameter will have to change somehow. If you want to use string interpolation, this answer shows that. So
template = $"Hello, {name}"; in which case you wouldn't need to use String.Format at all. Just make sure you define name before you define template.
Or you could use String.Format(template, name); like you have but you would need template = "Hello, {0}!";
The 0 is the index of the variable that will go in that position. For more info see String.Format
when specifying a format you use an index for the parameters that will follow. It is called a composite format string:
string template = "Hello, {0}!"
this makes it independent of variable names. But the true reason is that the overload of the Format method that you are using takes a params array as parameter as you can see in the method signature:
public static string Format (string format, params object?[] args);
so the index that is found in the template will be applied to extract the objects on the appropriate places from the array of objects that you pass into the method
If you want to use string.Format(), the template must be correct. Add the character $ at the beginning of the template:
try this:
string name = "Bob";
string template = $"Hello, {name}!";
Console.WriteLine(GetHelloGreeting(template, name)); // Hello, Bob!
public static string GetHelloGreeting(string template, string name)
{
return string.Format(template, name);
}
reult:
Hello, Bob!
Related
I have to manage a particular string formatting/padding condition. To be short I need to pad a string argument only if the argument length is 0. If I use the typical aligment parameter the padding is made if the length of the argument is smaller then the provided alignment value. For example:
string format = "#{0,10}#";
string argument;
string output;
argument = Console.ReadLine();
output = String.Format(format, argument);
String.WriteLine(output);
If I enter "try" as a value I got this result:
#try #
If I enter "trytrytrytry" I got:
#trytrytrytry#
What I would like to happen is depicted below:
Entering "" I would like to have:
# #
but entering "try" I would like to have:
#try#
The code I'm going to write should be as much generic as possibile since the format parameter is not static and is defined at runtime.
The best practice to do this is to define a custom string formatter. Unluckly it seems that the customization code can only act on the 'format' portion of the format parameter of the String.Format() method.
Indeed If I define a custom formatter:
public class EmptyFormatter : IFormatProvider, ICustomFormatter
{
public object GetFormat(Type formatType)
{
if (formatType == typeof(ICustomFormatter))
return this;
else
return null;
}
public string Format(string format, object arg, IFormatProvider formatProvider)
{
if (!this.Equals(formatProvider))
return null;
if (string.IsNullOrEmpty(format))
throw new ArgumentNullException();
return numericString;
}
}
The format and arg parameters of the Format method didn't contain the alignment parameter then I cannot actually check what lenght of the padding value should be applied and therefore I cannot act properly. Moreover this part of the 'formatting' of the string seems to be applied somewhere else but I have not idea where.
Is there a way to 'alter' this behaviour ?
A format item has the following syntax:
index[,alignment][ :formatString] }
The reason the format parameter is null is because there is no formatString component, there is only alignment. I couldn't find a way to access the alignment component from the Format method. However, one (ugly) solution is to set the formatString to be the same as the alignment, so that you can access it using the format parameter:
#{0,10:10}#
A less ugly solution would be to create your own method extension that first extracts the alignment from the given format and then calls the traditional String.Format method.
For example:
public static string StringFormat(this string Arg, string Format) {
//extract alignment from string
Regex reg = new Regex(#"{[-+]?\d+\,[-+]?(\d+)(?::[-+]?\d+)?}");
Match m = reg.Match(Format);
if (m != null) { //check if alignment exists
int allignment = int.Parse(m.Groups[1].Value); //get alignment
Arg = Arg.PadLeft(allignment); //pad left, you can make the length check here
Format = Format.Remove(m.Groups[1].Index - 1, m.Groups[1].Length + 1); //remove alignment from format
}
return (string.Format(Format, Arg));
}
To use the code:
string format = "#{0,10}#";
string argument = "try";
string output = argument.StringFormat(format); //"# try#"
I need to make a possibility to open a webpage either with an additional parameter or without one. If it has a parameter, I'll add it with the string.format function. Sometimes I need to format this parameter before opening the url, however, I don't want to make the code too specific.
The Parameter is always a string and I would need to cut the end of this string. Is it possible to do something in the string to be formatted to cut the unneeded text? If so how would the {0} have to look that it works?
string url = "http://foo.bar/xt:{0}";
string parameter = "abcdefghi";
if (Regex.Matches(Regex.Replace(url,
#"(\{{2}|\}{2})", ""), // removes escaped curly brackets
#"\{(\d+)(?:\:?[^}]*)\}")
.OfType<Match>().Any())
{
Process.Start(string.Format(url, parameter));
}
else
{
Process.Start(url);
}
Instead of abcdefghi I would like to have as parameter just abcdefg for instance. But this should be configurable via url. Something like {0:7) or so...
You have to write this kind of logic yourself. What you can do, however, is wrap this in an extension method so you don't have to duplicate it everywhere:
public static class StringExt
{
public static string Truncate(this string value, int maxLength)
{
if (string.IsNullOrEmpty(value)) return value;
return value.Length <= maxLength ? value : value.Substring(0, maxLength);
}
}
Now we can write:
var someString = "...";
someString = someString.Truncate(2);
I saw some code from a C# Console Application that can pass a string-valued parameter . My question is how can I create my own parametered method?
For example, the following code will pass the parameter value to {0} and print the string with value of Leonel.
Console.Write("{0}", "Leonel");
How can I make a method that can pass a parameter value to string format and return a parameterize string?
public string Combine(string format, params object[] args)
{
var parameterize = //("{0}", args) //I need something like this.
return parameterize;
}
I'm not totally clear on what you're asking, but would calling string.Format work?
string str = string.Format("The value is: {0}", val);
That should call the same underlying function as Console.Write does. It returns the string that would otherwise be printed to the Console. Given that, you probably don't even want your Combine method, as string.Format would take its place.
You can use the static method
string.Format(string str, params string[] formatters);
with your example:
public string Combine(string format, params object[] args)
{
var parameterize = string.Format(format, args);
return parameterize;
}
i have a following type of string format ---
Proposal is given to {Jwala Vora#3/13} for {Amazon Vally#2/11} {1#3/75} by {MdOffice employee#1/1}
the string contains pair of { } with different positions and may be n number of times.
now i want to replace that pair with other strings which i will compute depending on the string between { } pair.
how to do this ?
You could try regular expressions. Specifically, Regex.Replace variants using MatchEvaluator should do the trick. See http://msdn.microsoft.com/en-US/library/cft8645c(v=vs.80).aspx for more information.
Something along these lines:
using System;
using System.Text.RegularExpressions;
public class Replacer
{
public string Replace(string input)
{
// The regular expression passed as the second argument to the Replace method
// matches strings in the format "{value0#value1/value2}", i.e. three strings
// separated by "#" and "/" all surrounded by braces.
var result = Regex.Replace(
input,
#"{(?<value0>[^#]+)#(?<value1>[^/]+)/(?<value2>[^}]+)}",
ReplaceMatchEvaluator);
return result;
}
private string ReplaceMatchEvaluator(Match m)
{
// m.Value contains the matched string including the braces.
// This method is invoked once per matching portion of the input string.
// We can then extract each of the named groups in order to access the
// substrings of each matching portion as follows:
var value0 = m.Groups["value0"].Value; // Contains first value, e.g. "Jwala Vora"
var value1 = m.Groups["value1"].Value; // Contains second value, e.g. "3"
var value2 = m.Groups["value2"].Value; // Contains third value, e.g. "13"
// Here we can do things like convert value1 and value2 to integers...
var intValue1 = Int32.Parse(value1);
var intValue2 = Int32.Parse(value2);
// etc.
// Here we return the value with which the matching portion is replaced.
// This would be some function of value0, value1 and value2 as well as
// any other data in the Replacer class.
return "xyz";
}
}
public static class Program
{
public static void Main(string[] args)
{
var replacer = new Replacer();
var result = replacer.Replace("Proposal is given to {Jwala Vora#3/13} for {Amazon Vally#2/11} {1#3/75} by {MdOffice employee#1/1}");
Console.WriteLine(result);
}
}
This program will output Proposal is given to xyz for xyz xyz by xyz.
You'll need to provide your app-specific logic in the ReplaceMatchEvaluator method to process value0, value1 and value2 as appropriate. The class Replacer can contain additional members that can be used to implement the replacement logic in ReplaceMatchEvaluator. Strings are processed by calling Replace on an instance of the Replacer class.
Well you can split the string by '{' and '}' and determine the contents that way.
But i think a better way would be to find the chars by index and then you know the starting index and the end index of a pair or curly brackets so that way you can reconstruct the string with the placeholders replaced.
But the best method may be using Regex.Replace but that will only help to replace the placeholders with values you want but i think your requirement is to also parse the text inside of the curly brackets and based on that chose the value to be inserted so this won't work well perhaps. Find and Replace a section of a string with wildcard type search
You may use the Regex.Replace Method (String, String, MatchEvaluator) method and the {.*?} pattern. The following example uses a dictionary to replace the values, but you may replace this with your own logic.
class Program
{
static Dictionary<string, string> _dict = new Dictionary<string, string>();
static void Main(string[] args)
{
_dict.Add("{Jwala Vora#3/13}","someValue1");
_dict.Add("{Amazon Vally#2/11}", "someValue2");
_dict.Add("{1#3/75}", "someValue3");
_dict.Add("{MdOffice employee#1/1}", "someValue4");
var input = #"Proposal is given to {Jwala Vora#3/13} for {Amazon Vally#2/11} {1#3/75} by {MdOffice employee#1/1}";
var result = Regex.Replace(input, #"{.*?}", Evaluate);
Console.WriteLine(result);
}
private static string Evaluate(Match match)
{
return _dict[match.Value];
}
}
Cannot you do something with string.Format()?
For example
string.Format("Proposal is given to {0} for {1} {2} by {3}", "Jwala Vora", "Amazon Vally", 1, "MdOffice employee");
I am trying to create a generic formatter/parser combination.
Example scenario:
I have a string for string.Format(), e.g. var format = "{0}-{1}"
I have an array of object (string) for the input, e.g. var arr = new[] { "asdf", "qwer" }
I am formatting the array using the format string, e.g. var res = string.Format(format, arr)
What I am trying to do is to revert back the formatted string back into the array of object (string). Something like (pseudo code):
var arr2 = string.Unformat(format, res)
// when: res = "asdf-qwer"
// arr2 should be equal to arr
Anyone have experience doing something like this? I'm thinking about using regular expressions (modify the original format string, and then pass it to Regex.Matches to get the array) and run it for each placeholder in the format string. Is this feasible or is there any other more efficient solution?
While the comments about lost information are valid, sometimes you just want to get the string values of of a string with known formatting.
One method is this blog post written by a friend of mine. He implemented an extension method called string[] ParseExact(), akin to DateTime.ParseExact(). Data is returned as an array of strings, but if you can live with that, it is terribly handy.
public static class StringExtensions
{
public static string[] ParseExact(
this string data,
string format)
{
return ParseExact(data, format, false);
}
public static string[] ParseExact(
this string data,
string format,
bool ignoreCase)
{
string[] values;
if (TryParseExact(data, format, out values, ignoreCase))
return values;
else
throw new ArgumentException("Format not compatible with value.");
}
public static bool TryExtract(
this string data,
string format,
out string[] values)
{
return TryParseExact(data, format, out values, false);
}
public static bool TryParseExact(
this string data,
string format,
out string[] values,
bool ignoreCase)
{
int tokenCount = 0;
format = Regex.Escape(format).Replace("\\{", "{");
for (tokenCount = 0; ; tokenCount++)
{
string token = string.Format("{{{0}}}", tokenCount);
if (!format.Contains(token)) break;
format = format.Replace(token,
string.Format("(?'group{0}'.*)", tokenCount));
}
RegexOptions options =
ignoreCase ? RegexOptions.IgnoreCase : RegexOptions.None;
Match match = new Regex(format, options).Match(data);
if (tokenCount != (match.Groups.Count - 1))
{
values = new string[] { };
return false;
}
else
{
values = new string[tokenCount];
for (int index = 0; index < tokenCount; index++)
values[index] =
match.Groups[string.Format("group{0}", index)].Value;
return true;
}
}
}
You can't unformat because information is lost. String.Format is a "destructive" algorithm, which means you can't (always) go back.
Create a new class inheriting from string, where you add a member that keeps track of the "{0}-{1}" and the { "asdf", "qwer" }, override ToString(), and modify a little your code.
If it becomes too tricky, just create the same class, but not inheriting from string and modify a little more your code.
IMO, that's the best way to do this.
It's simply not possible in the generic case. Some information will be "lost" (string boundaries) in the Format method. Assume:
String.Format("{0}-{1}", "hello-world", "stack-overflow");
How would you "Unformat" it?
Assuming "-" is not in the original strings, can you not just use Split?
var arr2 = formattedString.Split('-');
Note that this only applies to the presented example with an assumption. Any reverse algorithm is dependent on the kind of formatting employed; an inverse operation may not even be possible, as noted by the other answers.
A simple solution might be to
replace all format tokens with (.*)
escape all other special charaters in format
make the regex match non-greedy
This would resolve the ambiguities to the shortest possible match.
(I'm not good at RegEx, so please correct me, folks :))
After formatting, you can put the resulting string and the array of objects into a dictionary with the string as key:
Dictionary<string,string []> unFormatLookup = new Dictionary<string,string []>
...
var arr = new string [] {"asdf", "qwer" };
var res = string.Format(format, arr);
unFormatLookup.Add(res,arr);
and in Unformat method, you can simply pass a string and look up that string and return the array used:
string [] Unformat(string res)
{
string [] arr;
unFormatLoopup.TryGetValue(res,out arr); //you can also check the return value of TryGetValue and throw an exception if the input string is not in.
return arr;
}