C - Substring index and length must refer to a location within the string

Question

I have a string that looks like   string url    www example com aaa bbb jpg      www example com   is 18 fixed in length  I want to get the  aaa bbb  part from this string  The actual url is not example nor aaa bbb though  the length may vary   so here s what I did   string newString   url Substring 18  url Length - 4     Then I got the exception  index and length must refer to a location within the string  What s wrong with my code and how to fix it  Thanks in advance

User · Answer

Try  This    int positionOfJPG url IndexOf   jpg     string newString   url Substring 18  url Length - positionOfJPG

User · Answer

You need to find the position of the first    and then calculate the portion you want   string url    www example com aaa bbb jpg   int Idx   url IndexOf       string yourValue   url Substring Idx   1  url Length - Idx - 4

User · Answer

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 doesn t match  you can either do something else or throw a meaningful error   Here s 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   amp  amp  url EndsWith suffix   amp  amp  url Length  gt    prefix Length   suffix Length         string newString   url Substring prefix Length  url Length - prefix Length - suffix Length       Console WriteLine newString     else       handle invalid state

User · Answer

You need to check your statement like this   string url    quot www example com aaa bbb jpg quot   string lenght   url Lenght-4  if url Lenght  gt  15   eg 15    string newString   url Substring 18  lenght

User · Answer

string newString   url Substring 18   url LastIndexOf      - 18

User · Answer

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

User · Answer

Here is another suggestion  If you can prepend http    to your url string you can do this    string path    http   www example com aaa bbb jpg     Uri uri   new Uri path                 string expectedString          uri PathAndQuery Remove uri PathAndQuery LastIndexOf

User · Answer

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

[c#] C# - Substring: index and length must refer to a location within the string

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