I am in the process of learning C++ in order to understand some open source code I have been given.
I came across a line as follows:
cmd << '\n'
cmd.stringpart << '\n'
See an operator as a function: For example, 3 + 4 calls a binary function taking two numbers and returning the sum of them.
Here, the author has created such a function to define the << operator, so that it can work with a cmd class instance as the left parameter, and a string as the right parameter. This is called "operator overloading". Look for operator<< occurrences in your code.
This can also be a member function of the cmd class, taking one parameter (still named operator<<).