XmResolvePartOffsets(3X)XmResolvePartOffsets(3X)NAMEXmResolvePartOffsets — A function that allows writing of upward-compat‐
ible applications and widgets
SYNOPSIS
#include <Xm/XmP.h>
void XmResolvePartOffsets (widget_class, offset) WidgetClasswid‐
get_class; XmOffsetPtr* offset;
VERSION
This page documents version 1.2 of the Motif library.
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 XmRe‐
solvePartOffsets 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 wid‐
get creates an offset resource list. To help you accomplish this, use
the XmPartResource structure and the XmPartOffset macro. The XmPartRe‐
source 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. XmPartRe‐
source 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 wid‐
get 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 initial‐
ized) 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 val‐
ues, 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) argu‐
ment, as illustrated here: XmField(w, offset, Label, text, char *) You
can define macros for each field to make this easier. Assume an inte‐
ger field xyz: #define BarXyz(w) (*(int *)(((char *) w) + \ off‐
set[BarIndex] + XtOffset(BarPart,xyz)))
The parameters for XmResolvePartOffsets are defined below: Specifies
the widget class pointer for the created widget. Returns the offset
record.
RELATED INFORMATIONXmResolveAllPartOffsets(3X).
XmResolvePartOffsets(3X)
