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I would like to know the different ways of inserting a variable into a string, in C#.
I am currently trying to insert values into a json string that I am building:
Random rnd = new Random();
int ID = rnd.Next(1, 999);
string body = #"{""currency"":""country"",""gold"":1,""detail"":""detailid-979095986"",""tId"":""help here""}";
How could I add the "ID" to the string body?
In a typical string inserting scenario, I'd do one of these:
string body = string.Format("My ID is {0}", ID);
string body = "My ID is " + ID;
However, your string is apparently JSON serialized data. I'd expect that I'd want to parse that into a class in order to work with it.
var myObj = JsonConvert.DeserializeObject<MyClass>(someString);
myObj.TID = ID;
// maybe do other things with it, then if I need JSON again...
string body = JsonConvert.SerializeObject(myObj);
One reason to take this approach is to make sure that any data I put in still makes the JSON valid. For example, if my ID were, instead of an int, a string with characters that needed escaping, directly inserting "\"\n\"" would not be the right thing to do.
String interpolation is the easiest way these days:
int myIntValue = 123;
string myStringValue = "one two three";
string interpolatedString = $"my int is: {myIntValue}. My string is: {myStringValue}.";
Output would be "my int is: 123. My string is: one two three.".
You can experiment with this sample yourself, over here.
The $ special character identifies a string literal as an interpolated
string. An interpolated string is a string literal that might contain
interpolation expressions. When an interpolated string is resolved to
a result string, items with interpolation expressions are replaced by
the string representations of the expression results. This feature is available starting with C# 6.
You could try this:
string body = #"{""currency"":""country"",""gold"":1,""detail"":""detailid-979095986"",""tId"":""" + ID + #"""}";
You can also use string.Concat:
string body = string.Concat(#"{""currency"":""country"",""gold"":1,""detail"":""detailid-979095986"",""tId"":""", ID, #"""}");
There are a number of ways to inject values into strings, however it's easy to lose sight of encodings, and cause major breakage.
If you just want to inject a value into another string, you can use:
string concatenation
string building
string formatting
Concatenation:
The simplest and most common way to build strings is by simply concatenating them together with the + operator:
var foo = 5;
var bar = "example-" + foo;
Concatenation can be difficult to read which makes it easy to introduce bugs, but for most simple tasks is the right tool for the job.
In this case, it's a poor choice:
string body = #"{""currency"":""country"",""gold"":1,""detail"":""detailid-979095986"",""tId"":""" + ID.ToString() + #"""}";
String Building
The StringBuilder class is useful for building large strings particularly when built iteratively.
var sb = new StringBuilder();
for (var i = 0; i < 1000; i++) {
sb.Append(i.ToString());
sb.Append(" ");
}
var output = sb.ToString();
It can still be difficult to read and hard to debug, but for cases where you're joining lots of strings together, it's super efficient
In this case, it's a poor choice:
StringBuilder sb = new StringBuilder();
sb.Append(#"{""currency"":""country"",""gold"":1,""detail"":""detailid-979095986"",""tId"":""");
sb.Append(ID.ToString());
sb.Append(#"""}");
string body = sb.ToString();
String formatting
The string.Format method makes templating data into a string super easy and efficient. If you plan on reusing the same string over and over, using a format string makes it much easier to read and debug code, particularly when there are lots of replacements:
var foo = 5;
var bar = string.Format("example-{0}", foo);
Format strings can also automatically apply culturally accurate formatting to particular data types, so that a DateTime is appropriately displayed, or so that a number has the appropriate number of trailing zeros.
In this case, it's a poor choice:
string string.Format(#"{""currency"":""country"",""gold"":1,""detail"":""detailid-979095986"",""tId"":""{0}""}", ID);
The right choice
You're not dumping data into any old string. That's JSON encoded data. If you just concatenate/build/format in any old value, you can break your string. For example, if the ID variable contained a " character, you'd break the entire JSON dataset.
Additionally, the length of the string and necessary quotes make it super difficult to read, which makes it difficult to maintain. Good luck when you get around to needing to add another formatted value, it's going to be a pain to change any existing value or add in new dynamic ones.
Instead of writing a JSON literal, write an object and encode it to JSON:
var bodyData =
new
{
currency = "country",
gold = 1,
detail = "detailid-979095986",
tId = ID //here's where you set the ID
};
var jss = new JavaScriptSerializer();
var body = jss.Serialize(bodyData);
This code is much easier to modify when the data changes, and will actually encode your data correctly. You don't need to worry about all those annoying double quote characters any more either.
You can use the
String.Format(#"{""currency"":""country"",""gold"":1,""detail"":""detailid-979095986"",""tId"":""{0}""}", ID)
Since this is params object[], you can use as many {n} as you want.
Instead of using on string, you could concatenate strings together using +, which would allow you to insert text between the generated strings.
string body = #"***" + ID + #"***";
I am working on a simple windows forms application that the user enters a string with delimiters and I parse the string and only get the variables out of the string.
So for example if the user enters:
2X + 5Y + z^3
I extract the values 2,5 and 3 from the "equation" and simply add them together.
This is how I get the integer values from a string.
int thirdValue
string temp;
temp = Regex.Match(variables[3], #"\d+").Value
thirdValue = int.Parse(temp);
variables is just an array of strings I use to store strings after parsing.
However, I get the following error when I run the application:
Input string was not in a correct format
Why i everyone moaning about this question and marking it down? it's incredibly easy to explain what is happening and the questioner was right to say it as he did. There is nothing wrong whatsoever.
Regex.Match(variables[3], #"\d+").Value
throws a Input string was not in a correct format.. FormatException if the string (here it's variables[3]) doesn't contain any numbers. It also does it if it can't access variables[3] within the memory stack of an Array when running as a service. I SUSPECT THIS IS A BUG The error is that the .Value is empty and the .Match failed.
Now quite honestly this is a feature masquerading as a bug if you ask me, but it's meant to be a design feature. The right way (IMHO) to have done this method would be to return a blank string. But they don't they throw a FormatException. Go figure. It is for this reason you were advised by astef to not even bother with Regex because it throws exceptions and is confusing. But he got marked down too!
The way round it is to use this simple additional method they also made
if (Regex.IsMatch(variables[3], #"\d+")){
temp = Regex.Match(variables[3], #"\d+").Value
}
If this still doesn't work for you you cannot use Regex for this. I have seen in a c# service that this doesn't work and throws incorrect errors. So I had to stop using Regex
I prefer simple and lightweight solutions without Regex:
static class Program
{
static void Main()
{
Console.WriteLine("2X + 65Y + z^3".GetNumbersFromString().Sum());
Console.ReadLine();
}
static IEnumerable<int> GetNumbersFromString(this string input)
{
StringBuilder number = new StringBuilder();
foreach (char ch in input)
{
if (char.IsDigit(ch))
number.Append(ch);
else if (number.Length > 0)
{
yield return int.Parse(number.ToString());
number.Clear();
}
}
yield return int.Parse(number.ToString());
}
}
you can change the string to char array and check if its a digit and count them up.
string temp = textBox1.Text;
char[] arra = temp.ToCharArray();
int total = 0;
foreach (char t in arra)
{
if (char.IsDigit(t))
{
total += int.Parse(t + "");
}
}
textBox1.Text = total.ToString();
This should solve your problem:
string temp;
temp = Regex.Matches(textBox1.Text, #"\d+", RegexOptions.IgnoreCase)[2].Value;
int thirdValue = int.Parse(temp);
Im still learning in C#, and there is one thing i cant really seem to find the answer to.
If i have a string that looks like this "abcdefg012345", and i want to make it look like "ab-cde-fg-012345"
i tought of something like this:
string S1 = "abcdefg012345";
string S2 = S1.Insert(2, "-");
string S3 = S2.Insert(6, "-");
string S4 = S3.Insert.....
...
..
Now i was looking if it would be possible to get this al into 1 line somehow, without having to make all those strings.
I assume this would be possible somehow ?
Whether or not you can make this a one-liner (you can), it will always cause multiple strings to be created, due to the immutability of the String in .NET
If you want to do this somewhat efficiently, without creating multiple strings, you could use a StringBuilder. An extension method could also be useful to make it easier to use.
public static class StringExtensions
{
public static string MultiInsert(this string str, string insertChar, params int[] positions)
{
StringBuilder sb = new StringBuilder(str.Length + (positions.Length*insertChar.Length));
var posLookup = new HashSet<int>(positions);
for(int i=0;i<str.Length;i++)
{
sb.Append(str[i]);
if(posLookup.Contains(i))
sb.Append(insertChar);
}
return sb.ToString();
}
}
Note that this example initialises StringBuilder to the correct length up-front, therefore avoiding the need to grow the StringBuilder.
Usage: "abcdefg012345".MultiInsert("-",2,5); // yields "abc-def-g012345"
Live example: http://rextester.com/EZPQ89741
string S1 = "abcdefg012345".Insert(2, "-").Insert(6, "-")..... ;
If the positions for the inserted strings are constant you could consider using string.Format() method. For example:
string strTarget = String.Format("abc{0}def{0}g012345","-");
string s = "abcdefg012345";
foreach (var index in [2, 6, ...]
{
s = s.Insert(index, "-");
}
I like this
StringBuilder sb = new StringBuilder("abcdefg012345");
sb.Insert(6, '-').Insert(2, '-').ToString();
String s1 = "abcdefg012345";
String seperator = "-";
s1 = s1.Insert(2, seperator).Insert(6, seperator).Insert(9, seperator);
Chaining them like that keeps your line count down. This works because the Insert method returns the string value of s1 with the parameters supplied, then the Insert function is being called on that returned string and so on.
Also it's worth noting that String is a special immutable class so each time you set a value to it, it is being recreated. Also worth noting that String is a special type that allows you to set it to a new instance with calling the constructor on it, the first line above will be under the hood calling the constructor with the text in the speech marks.
Just for the sake of completion and to show the use of the lesser known Aggregate function, here's another one-liner:
string result = new[] { 2, 5, 8, 15 }.Aggregate("abcdefg012345", (s, i) => s.Insert(i, "-"));
result is ab-cd-ef-g01234-5. I wouldn't recommend this variant, though. It's way too hard to grasp on first sight.
Edit: this solution is not valid, anyway, as the "-" will be inserted at the index of the already modified string, not at the positions wrt to the original string. But then again, most of the answers here suffer from the same problem.
You should use a StringBuilder in this case as Strings objects are immutable and your code would essentially create a completely new string for each one of those operations.
http://msdn.microsoft.com/en-us/library/2839d5h5(v=vs.71).aspx
Some more information available here:
http://www.dotnetperls.com/stringbuilder
Example:
namespace ConsoleApplication10
{
class Program
{
static void Main(string[] args)
{
StringBuilder sb = new StringBuilder("abcdefg012345");
sb.Insert(2, '-');
sb.Insert(6, '-');
Console.WriteLine(sb);
Console.Read();
}
}
}
If you really want it on a single line you could simply do something like this:
StringBuilder sb = new StringBuilder("abcdefg012345").Insert(2, '-').Insert(6, '-');
I have this code:
string str = "valta is the best place in the World";
I need to replace the first symbol. When I try this:
str[0] = 'M';
I received an error. How can I do this?
Strings are immutable, meaning you can't change a character. Instead, you create new strings.
What you are asking can be done several ways. The most appropriate solution will vary depending on the nature of the changes you are making to the original string. Are you changing only one character? Do you need to insert/delete/append?
Here are a couple ways to create a new string from an existing string, but having a different first character:
str = 'M' + str.Remove(0, 1);
str = 'M' + str.Substring(1);
Above, the new string is assigned to the original variable, str.
I'd like to add that the answers from others demonstrating StringBuilder are also very appropriate. I wouldn't instantiate a StringBuilder to change one character, but if many changes are needed StringBuilder is a better solution than my examples which create a temporary new string in the process. StringBuilder provides a mutable object that allows many changes and/or append operations. Once you are done making changes, an immutable string is created from the StringBuilder with the .ToString() method. You can continue to make changes on the StringBuilder object and create more new strings, as needed, using .ToString().
I suggest you to use StringBuilder class for it and than parse it to string if you need.
System.Text.StringBuilder strBuilder = new System.Text.StringBuilder("valta is the best place in the World");
strBuilder[0] = 'M';
string str=strBuilder.ToString();
You can't change string's characters in this way, because in C# string isn't dynamic and is immutable and it's chars are readonly. For make sure in it try to use methods of string, for example, if you do str.ToLower() it makes new string and your previous string doesn't change.
Strings are immutable. You can use the string builder class to help!:
string str = "valta is the best place in the World";
StringBuilder strB = new StringBuilder(str);
strB[0] = 'M';
While it does not answer the OP's question precisely, depending on what you're doing it might be a good solution. Below is going to solve my problem.
Let's say that you have to do a lot of individual manipulation of various characters in a string. Instead of using a string the whole time use a char[] array while you're doing the manipulation. Because you can do this:
char[] array = "valta is the best place in the World".ToCharArray();
Then manipulate to your hearts content as much as you need...
array[0] = "M";
Then convert it to a string once you're done and need to use it as a string:
string str = new string(array);
Merged Chuck Norris's answer w/ Paulo Mendonça's using extensions methods:
/// <summary>
/// Replace a string char at index with another char
/// </summary>
/// <param name="text">string to be replaced</param>
/// <param name="index">position of the char to be replaced</param>
/// <param name="c">replacement char</param>
public static string ReplaceAtIndex(this string text, int index, char c)
{
var stringBuilder = new StringBuilder(text);
stringBuilder[index] = c;
return stringBuilder.ToString();
}
I made a Method to do this
string test = "Paul";
test = ReplaceAtIndex(0, 'M', test);
// (...)
static string ReplaceAtIndex(int i, char value, string word)
{
char[] letters = word.ToCharArray();
letters[i] = value;
return string.Join("", letters);
}
str = "M" + str.Substring(1);
If you'll do several such changes use a StringBuilder or a char[].
(The threshold of when StringBuilder becomes quicker is after about 5 concatenations or substrings, but note that grouped concatenations of a + "b" + c + d + "e" + f are done in a single call and compile-type concatenations of "a" + "b" + "c" don't require a call at all).
It may seem that having to do this is horribly inefficient, but the fact that strings can't be changes allows for lots of efficiency gains and other advantages such as mentioned at Why .NET String is immutable?
I found a solution in unsafe context:
string str = "gg"; char c = 'H'; int index = 1;
fixed (char* arr = str) arr[index] = 'H';
Console.WriteLine(str);
It's so simple.
And in safe context:
string str = "gg"; char c = 'H'; int index = 1;
GCHandle handle = GCHandle.Alloc(str, GCHandleType.Pinned);
IntPtr arrAddress = handle.AddrOfPinnedObject();
Marshal.WriteInt16(arrAddress + index * sizeof(char), c);
handle.Free();
Console.WriteLine(str);
If speed is important, then you can do this:
String strValue = "$Some String Here!";
strValue = strValue.Remove(0, 1).Insert(0, "*");
This way, you don't really reconstruct the string, you keep the original object and just removing the first character and inserting a new one.
I usually approach it like this:
char[] c = text.ToCharArray();
for (i=0; i<c.Length; i++)
{
if (c[i]>'9' || c[i]<'0') // use any rules of your choice
{
c[i]=' '; // put in any character you like
}
}
// the new string can have the same name, or a new variable
String text=new string(c);
Can also be done using C# 8 ranges:
str = "M" + str[1..];
or + string interpolation:
str = $"M{str[1..]}";
I want to pass a string array (separated by commas), then use a function to split the passed array by a comma, and add in a delimiter in place of the comma.
I will show you what I mean in further detail with some broken code:
String FirstData = "1";
String SecondData = "2" ;
String ThirdData = "3" ;
String FourthData = null;
FourthData = AddDelimiter(FirstData,SecondData,ThirdData);
public String AddDelimiter(String[] sData)
{
// foreach ","
String OriginalData = null;
// So, here ... I want to somehow split 'sData' by a ",".
// I know I can use the split function - which I'm having
// some trouble with - but I also believe there is some way
// to use the 'foreach' function? I wish i could put together
// some more code here but I'm a VB6 guy, and the syntax here
// is killing me. Errors everywhere.
return OriginalData;
}
Syntax doesn't matter much here, you need to get to know the Base Class Library. Also, you want to join strings apparently, not split it:
var s = string.Join(",", arrayOFStrings);
Also, if you want to pass n string to a method like that, you need the params keyword:
public string Join( params string[] data) {
return string.Join(",", data);
}
To split:
string[] splitString = sData.Split(new char[] {','});
To join in new delimiter, pass in the array of strings to String.Join:
string colonString = String.Join(":", splitString);
I think you are better off using Replace, since all you want to do is replace one delimiter with another:
string differentDelimiter = sData.Replace(",", ":");
If you have several objects and you want to put them in an array, you can write:
string[] allData = new string[] { FirstData, SecondData, ThirdData };
you can then simply give that to the function:
FourthData = AddDelimiter(allData);
C# has a nice trick, if you add a params keyword to the function definition, you can treat it as if it's a function with any number of parameters:
public String AddDelimiter(params String[] sData) { … }
…
FourthData = AddDelimiter(FirstData, SecondData, ThirdData);
As for the actual implementation, the easiest way is to use string.Join():
public String AddDelimiter(String[] sData)
{
// you can use any other string instead of ":"
return string.Join(":", sData);
}
But if you wanted to build the result yourself (for example if you wanted to learn how to do it), you could do it using string concatenation (oneString + anotherString), or even better, using StringBuilder:
public String AddDelimiter(String[] sData)
{
StringBuilder result = new StringBuilder();
bool first = true;
foreach (string s in sData)
{
if (!first)
result.Append(':');
result.Append(s);
first = false;
}
return result.ToString();
}
One version of the Split function takes an array of characters. Here is an example:
string splitstuff = string.Split(sData[0],new char [] {','});
If you don't need to perform any processing on the parts in between and just need to replace the delimiter, you could easily do so with the Replace method on the String class:
string newlyDelimited = oldString.Replace(',', ':');
For large strings, this will give you better performance, as you won't have to do a full pass through the string to break it apart and then do a pass through the parts to join them back together.
However, if you need to work with the individual parts (to recompose them into another form that does not resemble a simple replacement of the delimiter), then you would use the Split method on the String class to get an array of the delimited items and then plug those into the format you wish.
Of course, this means you have to have some sort of explicit knowledge about what each part of the delimited string means.