Direct use of ''interp->result'' is now '''forbidden.''' An extension that scribbles on ''interp->result'' will get pointer smashes. All uses of ''interp->result'' have to be replaced with appropriate uses of ''Tcl_GetStringResult'' and ''Tcl_SetResult'' or their ''Tcl_Obj'' counterparts. In a header file of your C/C++ application or extension that includes the Tcl library, add these lines #include ... #if (TCL_MAJOR_VERSION < 8) #define Tcl_GetStringResult(interp) (interp->result) #endif Why? This helps you deprecate direct access to interp->result so you can upgrade your code written for Tcl 7 so it can be used with Tcl 8, yet still work with Tcl 7. <> Porting