1. use netstat -lntp to check opened port and the pid of running process
2. now we need to understand how to interact with the program named
3. vscode is really an amazing tool in reading source code with c++ plugins
4. learnt how to use #define and #ifdef
   https://www.jianshu.com/p/8ec776dc4e5d
5. use diff and patch command in linux to create a patch file

diff -rNu a b > diff.patch

a is the older dir or file
b is the edited dir or file

 patch -p0 < diff.patch

use this command to patch other files...