C++ structure

Is Edge(){} a function

Constructor. In C++, the member function declaration "No return type, function name with type name" is constructor. () is argumentless, and {} is the absence of actual processing in constructor.(The next line is a constructor with arguments.)

You may not be familiar with it if it comes from a proper(?) C++ code, but if you look at the books and sites that explain C++ from the basics, you will find many of them in this way.

If you could show us how well you know about C++, we might be able to add a little more.