XmResolvePartOffsets(3X) UNIX System V 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, (caddr_t)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:
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XmResolvePartOffsets(3X) UNIX System V XmResolvePartOffsets(3X)
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.
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