cppreference.com > C/C++ Pre-processor Commands > #line #line Syntax:
      #line line_number "filename"
The #line command is simply used to change the value of the __LINE__ and __FILE__ variables. The filename is optional. The __LINE__ and __FILE__ variables represent the current file and which line is being read. The command
       #line 10 "main.cpp"
changes the current line number to 10, and the current file to "main.cpp".