XmResolvePartOffsets - A function that allows writing of upward-compatible applications and widgets
#include <Xm/XmP.h> void XmResolvePartOffsets (widget_class, offset) WidgetClass widget_class; XmOffsetPtr * offset;
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:
XmPartResource resources[] = { { BarNxyz, BarCXyz, XmRBoolean, sizeof(Boolean), XmPartOffset(Bar,xyz), XmRImmediate, (XtPointer)False } };
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
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)))
The parameters for XmResolvePartOffsets are defined below: