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XmResolvePartOffsets(3X)      SDK X11 R4.11MU05     XmResolvePartOffsets(3X)


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

SYNOPSIS
       #include <Xm/XmP.h>

       void XmResolvePartOffsets (widget_class, offset)
            WidgetClasswidget_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, in place

         ·  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.


RELATED INFORMATION
       XmResolveAllPartOffsets(3X).


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