Please explain the process for better understanding if possible! Thank you!

Write a program in C++ that searches a text file (that has no spaces in it) named test.txt for the substring that is the longest without repeating characters. A program must be written in main to read and process input.txt, and then the output will be in output.txt. Create a function to determine the substring and length of the substring instead of writing the entire program in the main function. The output in output.txt must be formatted neatly as seen below (use setw). You may only use any of the following: iostream, iomanip, cmath, string, fstream, sstream, vector, cstdlib, ctime. Example: test.txt will contain: Pepperoni qwertyuiopq hi!! hhhhhhhh 2 Output.txt will contain the text from test.txt followed by the substring and \# of char in the substring