how to read a specific value from a file in C++?

I an newbie in C++ programming, I need to write a code to read a particular value from a file. for example if enter input as servername then it has to show ABCDE-1. I am trying with string function I am not able to get the results. Will anyone help in writing the logic.

I am not able to copy and paste the file data and code that I have written to read and print the data. So, I am attaching in screenshot. In that first part is file data Thank you enter image description here