XmResolvePartOffsets(library call)										XmResolvePartOffsets(library call)

NAME

       XmResolvePartOffsets -- A function that allows writing of upward-compatible applications and widgets

SYNOPSIS

       #include <Xm/Xm.h>
       void XmResolvePartOffsets(
       WidgetClass widget_class,
       XmOffsetPtr * offset);

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 XmResolvePartOffsets function allocates the offset records needed by	an
       application to guarantee upward-compatible access to widget instance records by applications and widgets.  These offset records are used by
       the widget to access all of the widget's variables.  A widget needs to take the steps described in the following paragraphs.

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

       XmPartResource resources[] = {
	 { BarNxyz, BarCXyz, XmRBoolean,
	   sizeof(Boolean), XmPartOffset(Bar,xyz),
	   XmRImmediate, (XtPointer)False }
       };

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

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

       The widget defines a variable, of type XmOffsetPtr, to point to the offset record.  This can be part of the widget's class record or a sep-
       arate global variable.

       In class initialization, the widget calls XmResolvePartOffsets, passing it a pointer to contain the address of the offset  record  and  the
       class record.  This does several 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 superclass
	     records

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

       The widget defines a constant that will be the index to its part structure in the offsets array.  The value should be 1	greater  than  the
       index of the widget's superclass.  Constants defined for all Xm widgets can be found in XmP.h.

       #define BarIndex (XmBulletinBIndex + 1)

       Instead of accessing fields directly, the widget must always go through the offset table.  The XmField macro helps you access these fields.
       Because the XmPartOffset and XmField macros concatenate things together, you must ensure that there is no space after  the  part  argument.
       For example, the following macros do not work because of the space after the part (Label) argument:

       XmField(w, offset, Label, text, char *)
       XmPartOffset(Label, text)

       Therefore, you must not have any spaces after the part (Label) argument, as illustrated here:

       XmField(w, offset, Label, text, char *)

       You can 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 parameters for XmResolvePartOffsets are

       widget_class
		 Specifies the widget class pointer for the created widget

       offset	 Returns the offset record

RELATED INFORMATION

       XmResolveAllPartOffsets(3).

														XmResolvePartOffsets(library call)