c# – Substring index and length must refer to a location within the string

c# – Substring index and length must refer to a location within the string

The second parameter in Substring is the length of the substring, not the end index.

You should probably include handling to check that it does indeed start with what you expect, end with what you expect, and is at least as long as you expect. And then if it doesnt match, you can either do something else or throw a meaningful error.

Heres some example code that validates that url contains your strings, that also is refactored a bit to make it easier to change the prefix/suffix to strip:

var prefix = www.example.com/;
var suffix = .jpg;
string url = www.example.com/aaa/bbb.jpg;

if (url.StartsWith(prefix) && url.EndsWith(suffix) && url.Length >= (prefix.Length + suffix.Length))
{
    string newString = url.Substring(prefix.Length, url.Length - prefix.Length - suffix.Length);
    Console.WriteLine(newString);
}
else
    //handle invalid state

Your mistake is the parameters to Substring. The first parameter should be the start index and the second should be the length or offset from the startindex.

string newString = url.Substring(18, 7);

If the length of the substring can vary you need to calculate the length.

Something in the direction of (url.Length - 18) - 4 (or url.Length - 22)

In the end it will look something like this

string newString = url.Substring(18, url.Length - 22);

c# – Substring index and length must refer to a location within the string

How about something like this :

string url = http://www.example.com/aaa/bbb.jpg;
Uri uri = new Uri(url);
string path_Query = uri.PathAndQuery;
string extension =  Path.GetExtension(path_Query);

path_Query = path_Query.Replace(extension, string.Empty);// This will remove extension

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