how to do substring in reverse mode in c#

Question

My string is "csm15+abc-indiaurban@v2". I want only "indiaurban" from my string. what I am doing right now is :

var lastindexofplusminus = input.LastIndexOfAny(new char[]{'+','-'});

var lastindexofattherate = input.LastIndexOf('@');

string sub = input.Substring(lastindexofplusminus,lastindexofattherate);

but getting error "Index and length must refer to a location within the string."

Thanks in Advance.

Answer 1

You should put the length in the second argument (instead of passing another index) of the Substring you want to grab. Given that you know the two indexes, the translation to the length is pretty straight forward:

string sub = input.Substring(lastindexofplusminus + 1, lastindexofattherate - lastindexofplusminus - 1);

Note, +1 is needed to get the char after your lastindexofplusminus.
-1 is needed to get the Substring between them minus the lastindexofattherate itself.

Answer 2

You can simple reverse the string, apply substring based on position and length, than reverse again.

string result = string.Join("", string.Join("", teste.Reverse()).Substring(1, 10).Reverse());

Or create a function:

public static string SubstringReverse(string str, int reverseIndex, int length) {
    return string.Join("", str.Reverse().Skip(reverseIndex - 1).Take(length));
}

View function working here!!