In the fourth installment of our series on cross-platform GUI programming with the Qt C++ toolkit, we are going to write a custom widget using Qt. The widget in question is a "scribble" widget (see Figure 1) - that is, the drawing area of a simple paint program

Recently, I've been thinking hard about what makes code maintainable, and how to write code to be maintainable. This interest has partly been driven by the mentoring of those starting out in C++ that I've been doing, both through the ACCU mentored developers program, and for work.

The principles I've identified have not really been hidden; since they've been widely documented for years, and they're actually things that most good developers do as a matter of course. However, as with many things, you don't necessarily realize their benefits until you rediscover them yourself.