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Get substring between first occurance of "A" and last occurance of "B"

I have a string which has two tokens that bound a substring that I want to extract, but the substring may contain the tokens themselves, so I want between the 1st occurrence of token A and the last occurrence of token B. I also need to search for the tokens in a case-insensitive search.
Tried to wrap my head around using regex to get this, but can't seem to figure it out. Not sure the best approach here. String.split won't work.
I can't modify the casing of the data between the tokens in the string.

Try this, (I've made it into an extension method)
public static string Between(this string value, string a, string b)
{
int posA = value.IndexOf(a);
int posB = value.LastIndexOf(b);
if (posA == -1) || (posB == -1)
{
return "";
}
int adjustedPosA = posA + a.Length;
return (adjustedPosA >= posB) ? "" : value.Substring(adjustedPosA, posB - adjustedPosA);
}
Usage would be:
var myString = "hereIsAToken_andThisIsWhatIwant_andSomeOtherToken";
var whatINeed = myString.Between("hereIsAToken_", "_andSomeOtherToken");

An easy way to approach this problem is the use of the indexOf function provided by the string class. IndexOf returns the first occurence, lastIndexOf as the name suggests, the last one.
string data;
string token1;
string token2;
int start = data.IndexOf(token1)+token1.Length;
int end = data.LastIndexOf(token2);
string result = data.Substring(start, end-start);
From my personal point of view, regex might be a bit overkill here, just try my example :)

How to remove character from string?

I have a string which is getting from a userInput. What I want to do now is removing a unique character from this string but only remove it once. The main problem is that this unique character doesn't have a unique index. For example:
User has input a string like : "0123456", and now I want to remove the first '1',so the string will be output like "023456". How ever, if a user input a string like "01123456", how can I remove the first '1' and make it looks like "0123456"? I am looking for a method that can be used for both of situation. I was using string.TrimStart(), but doesn't get what I want. How can I do this?

You could use Remove and IndexOf.
var str = "01123456";
var i = str.IndexOf('1'); // IndexOf returns -1 when there is no element found, so we need to handle that when calling remove.
var res = (i >= 0) ? str.Remove(i, 1) : str;
Console.WriteLine(res); // 0123456

I think you what you need is string.Remove method. See MSDN documentation here: https://learn.microsoft.com/en-us/dotnet/api/system.string.remove?view=netframework-4.7.2#System_String_Remove_System_Int32_System_Int32_
If you don't know where is your character, at first call string.IndexOf to find it. If this call returns nonnegaive number, call Remove to remove it. Just note that string is immutable so it will always create a new object.

yourstring = yourstring.IndexOf('1') != -1 ? yourstring.Remove(yourstring.IndexOf('1'), 1) : yourstring;

Another way would be to use a combination of Contains, Remove, and IndexOf:
if (userInput.Contains('1')) userInput = userInput.Remove(userInput.IndexOf('1'), 1);
Or if you want to be Linq-y...
userInput = string.Concat(userInput.TakeWhile(chr => chr != '1')
.Concat(userInput.SkipWhile(chr => chr != '1').Skip(1)));

substring from specific point of the string(from reverse side )

I wanted to substring from special point.
abcdef.png
I want
.png
Here i tried
string str = "abcdef.png";
str = str.Substring(0, str.Length - 4);
but then only shows the abcdef only BUT i want .png part

Just use the overload which takes a single parameter - the start point:
str = str.Substring(str.Length - 4);
Or better, use a method designed to get the extension of a filename - Path.GetExtension:
string extension = Path.GetExtension(str);

You can use Path.GetExtension method instead of substring.
string str = "abcdef.png";
string ext = Path.GetExtension(str); // .png

It seems you're dealing with file names, Use Path.GetExtension method for this purpose.

You need to pass str.Length - 4 as the first (and only) parameter, not as the second parameter:
str = str.Substring(str.Length - 4);
The way your code had it, you got a substring starting at zero, and containing str.Length - 4 characters.
If you want to take just the dot and the extension, use
str = str.Substring(str.LastIndexOf('.'));
expression.

If you want the extension of a filename use Path.GetExtension(str). Much easier.
http://msdn.microsoft.com/en-us/library/system.io.path.getextension(v=vs.110).aspx

try below code it will return the extension of file.
string extension = Path.GetExtension(str);

Substring, if the string is not long enough replace chars with spaces

I'm trying to compare first 3 chars of a string, i'm trying to use substring then compare.
The strings are read from an input file, and the string may not be 3 chars long. if an string is not 3 chars long i want the substring method to replace the empty chars with spaces.
How would i go about doing that.
Current code throws an exeption when the string is not long enough.

Use String.PadRight
myString.PadRight(3, ' ');
// do SubString here..
You could also create a .Left extension method that doesn't throw an exception when the string isn't big enough:
public static string Left(this string s, int len)
{
if (len == 0 || s.Length == 0)
return "";
else if (s.Length <= len)
return s;
else
return s.Substring(0, len);
}
Usage:
myString.Left(3);

Use one of the String.PadRight() methods before calling Substring():
string subString = myString.PadRight(3).Substring(0,3);
If you use the overload with one parameter like I did above, it will insert spaces.
string subString1 = string1.PadRight(3).Substring(0,3);
string subString2 = string2.PadRight(3).Substring(0,3);
if (String.Compare(subString1, subString2) == 0)
{
// if equal
}
else
{
// not equal
}
I used separate variables because it's a bit more readable, but you could in-line them in the if statement if you wanted to.

You can use this dirty hack:
var res = (myStr+" ").Substring(...);

Remove last characters from a string in C#. An elegant way?

I have a numeric string like this 2223,00. I would like to transform it to 2223. This is: without the information after the ",". Assume that there will be only two decimals after the ",".
I did:
str = str.Remove(str.Length - 3, 3);
Is there a more elegant solution? Maybe using another function? -I don´t like putting explicit numbers-

You can actually just use the Remove overload that takes one parameter:
str = str.Remove(str.Length - 3);
However, if you're trying to avoid hard coding the length, you can use:
str = str.Remove(str.IndexOf(','));

Perhaps this:
str = str.Split(",").First();

This will return to you a string excluding everything after the comma
str = str.Substring(0, str.IndexOf(','));
Of course, this assumes your string actually has a comma with decimals. The above code will fail if it doesn't. You'd want to do more checks:
commaPos = str.IndexOf(',');
if(commaPos != -1)
str = str.Substring(0, commaPos)
I'm assuming you're working with a string to begin with. Ideally, if you're working with a number to begin with, like a float or double, you could just cast it to an int, then do myInt.ToString() like:
myInt = (int)double.Parse(myString)
This parses the double using the current culture (here in the US, we use . for decimal points). However, this again assumes that your input string is can be parsed.

String.Format("{0:0}", 123.4567); // "123"
If your initial value is a decimal into a string, you will need to convert
String.Format("{0:0}", double.Parse("3.5", CultureInfo.InvariantCulture)) //3.5
In this example, I choose Invariant culture but you could use the one you want.
I prefer using the Formatting function because you never know if the decimal may contain 2 or 3 leading number in the future.
Edit: You can also use Truncate to remove all after the , or .
Console.WriteLine(Decimal.Truncate(Convert.ToDecimal("3,5")));

Use:
public static class StringExtensions
{
/// <summary>
/// Cut End. "12".SubstringFromEnd(1) -> "1"
/// </summary>
public static string SubstringFromEnd(this string value, int startindex)
{
if (string.IsNullOrEmpty(value)) return value;
return value.Substring(0, value.Length - startindex);
}
}
I prefer an extension method here for two reasons:
I can chain it with Substring.
Example: f1.Substring(directorypathLength).SubstringFromEnd(1)
Speed.

You could use LastIndexOf and Substring combined to get all characters to the left of the last index of the comma within the sting.
string var = var.Substring(0, var.LastIndexOf(','));

You can use TrimEnd. It's efficient as well and looks clean.
"Name,".TrimEnd(',');

Try the following. It worked for me:
str = str.Split(',').Last();

Since C# 8.0 it has been possible to do this with a range operator.
string textValue = "2223,00";
textValue = textValue[0..^3];
Console.WriteLine(textValue);
This would output the string 2223.
The 0 says that it should start from the zeroth position in the string
The .. says that it should take the range between the operands on either side
The ^ says that it should take the operand relative to the end of the sequence
The 3 says that it should end from the third position in the string

Use lastIndexOf. Like:
string var = var.lastIndexOf(',');