Say you declare your class in a header file. Some member functions are big, some medium, some small, and some with a single line (public accessor). My book suggests that professional code tend to have the smaller code within the header, and the bigger functions are defined within its equivalent .cpp file. Is that really common practice? I know some people who are religious with putting everything in a cpp file. Is this really the common way to do things? It would save space in the cpp file anyway.