Page to record guidelines for adapting C source code to deal with the CONST-ified interfaces of Tcl/Tk 8.4.
Most stuff can be fixed by putting CONST (or, if you're unlucky, CONST84) in your types. Sometimes you might need to add a cast. Anything that traditionally worked, will continue to work. There's also a symbol you can #define to switch off the constness in the interface (whose name I don't remember)
See also Changes in Tcl/Tk 8.4