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XmResolvePartOffsets(3X)
OSF/Motif
NAME
  XmResolvePartOffsets - A function that allows writing of upward-compatible
  applications and widgets

SYNOPSIS
  #include <Xm/XmP.h>

  void XmResolvePartOffsets (widget_class, offset)
	  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
  following steps:

    ·  Instead of creating a resource list, the widget creates an offset
       resource list. To help you 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 offset, it has two shorts. This 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
       separate 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:

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

	 -- Allocates an array based upon the number of superclasses.

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

	 -- Uses the part offset array to modify the offset entries in the
	    resource list to be real offsets.

    ·  The widget defines a constant which 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 defined below:

  widget_class
      Specifies the widget class pointer for the created widget.

  offset
      Returns the offset record.

SEE ALSO
  XmResolveAllPartOffsets(3X)

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