#include <Xm/XmP.h> void XmResolveAllPartOffsets (widget_class, offset, constraint_offset) WidgetClass widget_class; XmOffsetPtr * offset; XmOffsetPtr * constraint_offset;
The use of offset records requires two extra global variables per widget class. The variables consist of pointers to arrays of offsets into the widget record and constraint record for each part of the widget structure. The XmResolveAllPartOffsets function allocates the offset records needed by an application to guarantee upward-compatible access to widget instance and constraint 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:
If the widget is a subclass of the Constraint class and it defines additional constraint resources, create an offset resource list for the constraint part as well. Instead of using XtOffset for the offset, the widget uses XmConstraintPartOffset in the constraint resource list.
XmPartResource resources[] = { { BarNxyz, BarCXyz, XmRBoolean, sizeof(Boolean), XmPartOffset(Bar,xyz), XmRImmediate, (XtPointer)False } }; XmPartResource constraints[] = { { BarNmaxWidth, BarNMaxWidth, XmRDimension, sizeof(Dimension), XmConstraintPartOffset(Bar,max_width), XmRImmediate, (XtPointer)100 } };
Adds the superclass (which, by definition, has already been initialized) size field to the part size field
If the widget is a subclass of the Constraint class, adds the superclass constraint size field to the constraint size field
Allocates an array based upon the number of superclasses
If the widget is a subclass of the constraint class, allocates an array for the constraint offset record
Fills in the offsets of all the widget parts and constraint 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
XmP.h
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#define BarIndex (XmBulletinBIndex + 1)
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)))
For constraint field max_width:
#define BarMaxWidth(w) \ XmConstraintField(w,constraint_offsets,Bar,max_width,Dimension)
The parameters for XmResolveAllPartOffsets are defined below: