Programming Microsoft Visual C++

In a normal application, you write code for software components that solve particular problems. It's usually a simple matter of meeting the project specification. With reusable base classes, however, you must anticipate future programming needs, both your own and those of others. You have to write a class that is general and complete yet efficient and easy to use.

This chapter's example showed me the difficulty in building reusable software. I started out intending to write a frame class that would "remember" its window size and position. When I got into the job, I discovered that existing Windows-based programs remember whether they have been minimized to the taskbar or whether they have been maximized to full screen. Then there was the oddball case of a window that was both minimized and maximized. After that, I had to worry about the toolbar and the status bar, plus the class had to work in a dynamic link library (DLL). In short, it was surprisingly difficult to write a frame class that would do everything that a programmer might expect.

In a production programming environment, reusable base classes might fall out of the normal software development cycle. A class written for one project might be extracted and further generalized for another project. There's always the temptation, though, to cut and paste existing classes without asking, "What can I factor out into a base class?" If you're in the software business for the long term, it's beneficial to start building your library of truly reusable components.