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)
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 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.
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 initial‐
ization, 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 num‐
ber 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: Specifies
the widget class pointer for the created widget. Returns the offset
record.
SEE ALSOXmResolveAllPartOffsets(3X)XmResolvePartOffsets(3X)
