ultrix man page for dwtresolvepartoffsets

DwtResolvePartOffsets(3Dwt)											       DwtResolvePartOffsets(3Dwt)

Name
       DwtResolvePartOffsets - Allows writing of upward-compatible applications and widgets.

Syntax
       void DwtResolvePartOffsets(widget_class, offset)
	    WidgetClass widget_class;
	    DwtOffsetPtr *offset;

Arguments
       widget_class
		 Specifies the widget class pointer for the created widget.

       offset	 Specifies the offset record.

Description
       The  use  of offset records requires one extra global variable per widget class.  The variable consists of a pointer to an array of offsets
       into the widget record for each part of the widget structure.  The DwtResolvePartOffsets function allocates the offset records needed by an
       application to guarantee upward-compatible applications and widgets.  These offset records are used by the widget to access all of the wid-
       get's variables.  A widget needs to take the following steps:

       o    Instead of creating a resource list, the widget creates an offset resource list.  To help you accomplish this, use the DwtPartResource
	    structure  and the DwtPartOffset macro.  The DwtPartResource data structure looks just like a resource list, but instead of having one
	    integer for its offset, it has two shorts.	This gets put into the class record as if it were a  normal  resource  list.   Instead	of
	    using XtOffset for the offset, it uses DwtPartOffset.

       o    Instead of putting the widget size in the class record, the widget puts the widget part in the same field.

       o    Instead of putting XtVersion in the class record, the widget puts XtVersionDontCheck in the class record.

       o    The widget defines a variable to point to the offset record.  This can be part of the widget's class record or a separate global vari-
	    able.

       o    In class initialization, the widget calls DwtResolvePartOffsets, passing it the offset address and the class record.  This	does  sev-
	    eral things:

       o	 Adds the superclass (which, by definition, has already been initialized) size field to the part size field.

       o    Allocates an array based upon the number of superclasses.

       o	 Fills	in  the offsets of all the widget parts with the appropriate values, determined by examining the size fields of all super-
		 class records.

       o	 Uses the part offset array to modify the offset entries in the resource list to be real offsets, in place.

       o    Instead of accessing fields directly, the widget must always go through the offset table.  You will probably define  macros  for  each
	    field to make this easier.	Assume an integer field ``xyz'':
	    #define BarXyz(w) (*(int *)(((char *) w) + offset[BarIndex] + 
			XtOffset(BarPart,xyz)))

	    The  DwtField  macro  helps  you  access  these fields.  Because the DwtPartOffset and DwtField macros concatenate arguments, you must
	    ensure there is no space before or after the part argument.  For example, the following do not work because of  the  space	before	or
	    after the part (Label) argument:
	    DwtField(w, offset, Label, text, char *)
	    DwtPartOffset( Label, text).
	    Therefore, you must not have any spaces before or after the part (Label) argument, as illustrated here:
	    DwtField(w, offset,Label, text, char *)

See Also
       Guide to the XUI Toolkit: C Language Binding
       Guide to the XUI Toolkit Intrinsics: C Language Binding

														       DwtResolvePartOffsets(3Dwt)