Practical Programming in Tcl and Tk, Fourth Edition

Chapter 49. Writing a Tk Widget in C

This chapter describes the implementation of a simple clock widget. Two implementations are shown: the original string-based command interface and the Tcl_Obj command interface.

A custom widget implemented in C has the advantage of being efficient and flexible. However, it requires more work, too. This chapter illustrates the effort by explaining the implementation of a clock widget. It is a digital clock that displays the current time according to a format string. This is something you could implement in several lines of Tcl using a label widget, the clock command, and after for periodic updates. However, the point of the example is to show the basic structure for a Tk widget implemented in C, not how much ...