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\&
.sp 1
.ce 3
\s+1\fBChapter 11\fP\s-1

\s+1\fBUtility Functions\fP\s-1
.sp 2
.nr H1 11
.nr H2 0
.nr H3 0
.nr H4 0
.nr H5 0
.LP
.XS
Chapter 11 \(em Utility Functions
.XE
The \*(xI provide a number of utility functions that you can use to
.IP \(bu 5
Determine the number of elements in an array.
.IP \(bu 5
Translate strings to widget instances.
.IP \(bu 5
Manage memory usage.
.IP \(bu 5
Share graphics contexts.
.IP \(bu 5
Manipulate selections.
.IP \(bu 5
Merge exposure events into a region.
.IP \(bu 5
Translate widget coordinates.
.IP \(bu 5
Locate a widget given a window id.
.IP \(bu 5
Handle errors.
.IP \(bu 5
Set the WM_COLORMAP_WINDOWS property.
.IP \(bu 5
Locate files by name with string substitutions.
.IP \(bu 5
Register callback functions for external agents.
.IP \(bu 5
Locate all the displays of an application context.

.NH 2
Determining the Number of Elements in an Array
.XS
\fB\*(SN Determining the Number of Elements in an Array\fP
.XE
.LP
To determine the number of elements in a fixed-size array, use
.PN XtNumber .
.LP
.IN "XtNumber" "" "@DEF@"
.sM
.FD 0
Cardinal XtNumber(\fIarray\fP)
.br
      \fIArrayType array\fP;
.FN
.IP \fIarray\fP 1i
Specifies a fixed-size array of arbitrary type.
.LP
.eM
The
.PN XtNumber
macro returns the number of elements allocated to the array.

.NH 2
Translating Strings to Widget Instances
.XS
\fB\*(SN Translating Strings to Widget Instances\fP
.XE
.LP
To translate a widget name to a widget instance, use
.PN XtNameToWidget .
.LP
.IN "XtNameToWidget" "" "@DEF@"
.sM
.FD 0
Widget XtNameToWidget(\fIreference\fP, \fInames\fP)
.br
      Widget \fIreference\fP;
.br
      String \fInames\fP;
.FN
.IP \fIreference\fP 1i
Specifies the widget from which the search is to start.  \*(cI
.IP \fInames\fP 1i
Specifies the partially qualified name of the desired widget.
.LP
.eM
The
.PN XtNameToWidget
function searches for a descendant of the \fIreference\fP
widget whose name matches the specified names.  The \fInames\fP parameter
specifies a simple object name or a series of simple object name
components separated by periods or asterisks.
.PN XtNameToWidget
returns the descendant with the shortest name matching the specification
according to the following rules, where child is either a pop-up child
or a normal child if the widget's class is a subclass of
Composite :
.IP \(bu 5
Enumerate the object subtree rooted at the reference widget in
breadth-first order, qualifying the name of each object with the
names of all its ancestors up to, but not including, the reference
widget.  The ordering between children of a common parent is
not defined.
.IP \(bu 5
Return the first object in the enumeration that matches the
specified name, where each component of \fInames\fP matches exactly the
corresponding component of the qualified object name and asterisk
matches any series of components, including none.
.IP \(bu 5
If no match is found, return NULL.
.LP
Since breadth-first traversal is specified, the descendant with the
shortest matching name (i.e., the fewest number of components), if any,
will always be returned.  However, since the order of enumeration of
children is undefined and since the \*(xI do not require that all
children of a widget have unique names,
.PN XtNameToWidget
may return any
child that matches if there are multiple objects in the subtree with
the same name.  Consecutive separators (periods or asterisks)
including at least one asterisk are treated as a single asterisk.
Consecutive periods are treated as a single period.

.NH 2
Managing Memory Usage
.XS
\fB\*(SN Managing Memory Usage\fP
.XE
.LP
The \*(xI memory management functions provide uniform checking for
null pointers and error reporting on memory allocation errors.
These functions are completely compatible with their standard C language 
runtime counterparts
.PN malloc ,
.PN calloc ,
.PN realloc ,
and
.PN free
with the following added functionality:
.IP \(bu 5
.PN XtMalloc ,
.PN XtCalloc ,
and
.PN XtRealloc
give an error if there is not enough memory.
.IP \(bu 5
.PN XtFree
simply returns if passed a NULL pointer.
.IP \(bu 5
.PN XtRealloc
simply allocates new storage if passed a NULL pointer.
.LP
See the standard C library documentation on
.PN malloc ,
.PN calloc ,
.PN realloc ,
and
.PN free
for more information.
.sp
.LP
To allocate storage, use
.PN XtMalloc .
.LP
.IN "XtMalloc" "" "@DEF@"
.sM
.FD 0
char *XtMalloc(\fIsize\fP)
.br
      Cardinal \fIsize\fP;
.FN
.IP \fIsize\fP 1i
Specifies the number of bytes desired.
.LP
.eM
The
.PN XtMalloc
function returns a pointer to a block of storage of at least 
the specified \fIsize\fP bytes.
If there is insufficient memory to allocate the new block,
.PN XtMalloc
calls
.PN XtErrorMsg .
.sp
.LP
To allocate and initialize an array, use
.PN XtCalloc .
.LP
.IN "XtCalloc" "" "@DEF@"
.sM
.FD 0
char *XtCalloc(\fInum\fP, \fIsize\fP)
.br
      Cardinal \fInum\fP;
.br
      Cardinal \fIsize\fP;
.FN
.IP \fInum\fP 1i
Specifies the number of array elements to allocate.
.IP \fIsize\fP 1i
Specifies the size of each array element in bytes.
.LP
.eM
The
.PN XtCalloc
function allocates space for the specified number of array elements 
of the specified size and initializes the space to zero.
If there is insufficient memory to allocate the new block,
.PN XtCalloc
calls
.PN XtErrorMsg .
.PN XtCalloc
returns the address of the allocated storage.
.sp
.LP
To change the size of an allocated block of storage, use
.PN XtRealloc .
.LP
.IN "XtRealloc" "" "@DEF@"
.sM
.FD 0
char *XtRealloc(\fIptr\fP, \fInum\fP)
.br
      char *\fIptr\fP;
.br
      Cardinal \fInum\fP;
.FN
.IP \fIptr\fP 1i
Specifies a pointer to the old storage allocated with
.PN XtMalloc ,
.PN XtCalloc ,
or
.PN XtRealloc ,
or NULL.
.IP \fInum\fP 1i
Specifies number of bytes desired in new storage.
.LP
.eM
The
.PN XtRealloc
function changes the size of a block of storage, possibly moving it.
Then it copies the old contents (or as much as will fit) into the new block
and frees the old block.
If there is insufficient memory to allocate the new block,
.PN XtRealloc
calls
.PN XtErrorMsg .
If \fIptr\fP is NULL,
.PN XtRealloc
simply calls
.PN XtMalloc .
.PN XtRealloc
then returns the address of the new block.
.sp
.LP
To free an allocated block of storage, use
.PN XtFree .
.LP
.IN "XtFree" "" "@DEF@"
.sM
.FD 0
void XtFree(\fIptr\fP)
.br
      char *\fIptr\fP;
.FN
.IP \fIptr\fP 1i
Specifies a pointer to a block of storage allocated with
.PN XtMalloc ,
.PN XtCalloc ,
or
.PN XtRealloc ,
or NULL.
.LP
.eM
The
.PN XtFree
function returns storage, allowing it to be reused.
If \fIptr\fP is NULL,
.PN XtFree
returns immediately.
.sp
.LP
To allocate storage for a new instance of a type, use
.PN XtNew .
.LP
.IN "XtNew" "" "@DEF@"
.sM
.FD 0
\fItype\fP *XtNew(\fItype\fP)
.br
      \fItype t\fP;
.FN
.IP \fItype\fP 1i
Specifies a previously declared type.
.LP
.eM
.PN XtNew
returns a pointer to the allocated storage.
If there is insufficient memory to allocate the new block,
.PN XtNew
calls
.PN XtErrorMsg .
.PN XtNew
is a convenience macro that calls
.PN XtMalloc
with the following arguments specified:
.LP
.Ds
.TA .5i
.ta .5i
((type *) XtMalloc((unsigned) sizeof(type)))
.De
.LP
The storage allocated by
.PN XtNew
should be freed using
.PN XtFree .
.sp
.LP
To copy an instance of a string, use
.PN XtNewString .
.LP
.IN "XtNewString" "" "@DEF@"
.sM
.FD 0
String XtNewString(\fIstring\fP)
.br
      String \fIstring\fP;
.FN
.IP \fIstring\fP 1i
Specifies a previously declared string.
.LP
.eM
.PN XtNewString
returns a pointer to the allocated storage.
If there is insufficient memory to allocate the new block,
.PN XtNewString
calls
.PN XtErrorMsg .
.PN XtNewString
is a convenience macro that calls
.PN XtMalloc
with the following arguments specified:
.LP
.Ds 
.TA .5i
.ta .5i
(strcpy(XtMalloc((unsigned)strlen(str) + 1), str))
.De
.LP
The storage allocated by
.PN XtNewString
should be freed using
.PN XtFree .

.NH 2
Sharing Graphics Contexts
.XS
\fB\*(SN Sharing Graphics Contexts\fP
.XE
.LP
The \*(xI provide a mechanism whereby cooperating objects can share a
graphics context (GC), thereby reducing both the number of GCs
created and the total number of server calls in any given application.
The mechanism is a simple caching scheme
and allows for clients to declare both modifiable and nonmodifiable
fields of the shared GCs.
.LP
To obtain a shareable GC with modifiable fields, use
.PN XtAllocateGC .
.LP
.IN "XtAllocateGC" "" "@DEF@"
.sM
.FD 0
GC XtAllocateGC(\fIwidget\fP, \fIdepth\fP, \fIvalue_mask\fP, \fIvalues\fP, \
\fIdynamic_mask\fP, \fIunused_mask\fP)
.br
      Widget \fIobject\fP;
.br
      Cardinal \fIdepth\fP;
.br
      XtGCMask \fIvalue_mask\fP;
.br
      XGCValues *\fIvalues\fP;
.br
      XtGCMask \fIdynamic_mask\fP;
.br
      XtGCMask \fIunused_mask\fP;
.FN
.IP \fIobject\fP 1i
Specifies an object, giving the screen for which the
returned GC is valid.  \*(oI
.IP \fIdepth\fP 1i
Specifies the depth for which the returned GC is valid, or 0.
.IP \fIvalue_mask\fP 1i
Specifies fields of the GC that are initialized from \fIvalues\fP.
.IP \fIvalues\fP 1i
Specifies the values for the initialized fields.
.IP \fIdynamic_mask\fP 1i
Specifies fields of the GC that will be modified by the caller.
.IP \fIunused_mask\fP 1i
Specifies fields of the GC that will not be needed by the caller.
.LP
.eM
The
.PN XtAllocateGC
function returns a shareable GC that may be
modified by the client.  The \fIscreen\fP field of the specified
widget or of the nearest widget ancestor of the specified
object and the specified \fIdepth\fP argument supply
the root and drawable depths for which the GC is to be
valid.  If \fIdepth\fP is zero, the depth is taken from the
\fIdepth\fP field of the specified widget or of the nearest
widget ancestor of the specified object.
.LP
The \fIvalue_mask\fP argument specifies fields of the GC
that are initialized with the respective member of the
\fIvalues\fP structure.  The \fIdynamic_mask\fP argument specifies fields
that the caller intends to modify during program execution.
The caller must ensure that the corresponding GC field is set
prior to each use of the GC.  The \fIunused_mask\fP argument
specifies fields of the GC that are of no interest to the
caller.  The caller may make no assumptions about the contents
of any fields specified in \fIunused_mask\fP.  The caller may assume
that at all times all fields not specified in either
\fIdynamic_mask\fP or \fIunused_mask\fP have their default value if not
specified in \fIvalue_mask\fP or the value specified by \fIvalues\fP.
If a field is specified in both \fIvalue_mask\fP and \fIdynamic_mask\fP,
the effect is as if it were specified only in \fIdynamic_mask\fP
and then immediately set to the value in \fIvalues\fP.  If a field
is set in \fIunused_mask\fP and also in either \fIvalue_mask\fP or
\fIdynamic_mask\fP, the specification in \fIunused_mask\fP is ignored.
.LP
.PN XtAllocateGC
tries to minimize the number of unique GCs
created by comparing the arguments with those of previous
calls and returning an existing GC when there are no
conflicts.
.PN XtAllocateGC
may modify and return an existing GC if it was allocated with a
nonzero \fIunused_mask\fP.
.sp
.LP
To obtain a shareable GC with no modifiable fields, use
.PN XtGetGC .
.LP
.IN "XtGetGC" "" "@DEF@"
.sM
.FD 0
GC XtGetGC(\fIobject\fP, \fIvalue_mask\fP, \fIvalues\fP)
.br
      Widget \fIobject\fP;
.br
      XtGCMask \fIvalue_mask\fP;
.br
      XGCValues *\fIvalues\fP;
.FN
.IP \fIobject\fP 1i
Specifies an object, giving the screen and depth for which the
returned GC is valid.  \*(oI
.IP \fIvalue_mask\fP 1i
Specifies which fields of the \fIvalues\fP structure are specified.
.IP \fIvalues\fP 1i
Specifies the actual values for this GC.
.LP
.eM
The
.PN XtGetGC
function returns a shareable, read-only GC.
The parameters to this function are the same as those for
.PN XCreateGC 
except that an Object is passed instead of a Display.
.PN XtGetGC
is equivalent to
.PN XtAllocateGC
with \fIdepth\fP, \fIdynamic_mask\fP, and \fIunused_mask\fP all zero.
.LP
.PN XtGetGC
shares only GCs in which all values in the GC returned by
.PN XCreateGC
are the same.
In particular, it does not use the \fIvalue_mask\fP provided to
determine which fields of the GC a widget considers relevant.
The \fIvalue_mask\fP is used only to tell the server which fields should be
filled in from \fIvalues\fP and which it should fill in with default values.
.sp
.LP
To deallocate a shared GC when it is no longer needed, use
.PN XtReleaseGC .
.LP
.IN "XtReleaseGC" "" "@DEF@"
.sM
.FD 0
void XtReleaseGC(\fIobject\fP, \fIgc\fP)
.br
      Widget \fIobject\fP;
.br
      GC \fIgc\fP;
.FN
.IP \fIobject\fP 1i
Specifies any object on the Display for which the GC was created.  \*(oI
.IP \fIgc\fP 1i
Specifies the shared GC obtained with either
.PN XtAllocateGC
or
.PN XtGetGC .
.LP
.eM
References to shareable GCs are counted and a free request is generated to the
server when the last user of a given GC releases it.

.NH 2
Managing Selections
.XS
\*(SN Managing Selections
.XE
.LP
Arbitrary widgets in multiple applications can communicate 
with each other by means of the \*(xI global selection mechanism,
which conforms to the specifications in the \fI\*(xC\fP.
The \*(xI supply functions for providing and receiving selection data in
one logical piece (atomic transfers)
or in smaller logical segments (incremental transfers).
.LP
The incremental interface is provided for a selection owner or
selection requestor that cannot or prefers not to pass the selection
value to and from the \*(xI in a single call.  For instance,
either an application that is running on a machine with limited memory
may not be able to store the entire selection value in memory or a
selection owner may already have the selection value available in
discrete chunks, and it would be more efficient not to have to
allocate additional storage to copy the pieces contiguously.  Any
owner or requestor that prefers to deal with the selection value in
segments can use the incremental interfaces to do so.
The transfer between the selection owner or requestor and the \*(xI is not
required to match the underlying
transport protocol between the application and the X server;
the \*(xI will break too large a selection 
into smaller pieces for transport if necessary
and will coalesce a selection transmitted incrementally if the value
was requested atomically.

.NH 3
Setting and Getting the Selection Timeout Value
.XS
\fB\*(SN Setting and Getting the Selection Timeout Value\fP
.XE
.LP
To set the \*(xI selection timeout, use
.PN XtAppSetSelectionTimeout .
.LP
.IN "XtAppSetSelectionTimeout" "" "@DEF@"
.sM
.FD 0
void XtAppSetSelectionTimeout(\fIapp_context\fP, \fItimeout\fP)
.br
    XtAppContext \fIapp_context\fP;
.br
    unsigned long \fItimeout\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fItimeout\fP 1i
Specifies the selection timeout in milliseconds.
.eM
.LP
To get the current selection timeout value, use
.PN XtAppGetSelectionTimeout .
.LP
.IN "XtAppGetSelectionTimeout" "" "@DEF@"
.sM
.FD 0
unsigned long XtAppGetSelectionTimeout(\fIapp_context\fP)
.br
     XtAppContext \fIapp_context\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.LP
.eM
The
.PN XtAppGetSelectionTimeout
function returns the current selection timeout value in milliseconds.
The selection timeout is the time within which the two communicating 
applications must respond to one another.
The initial timeout value is set by the 
selectionTimeout
.IN "selectionTimeout"
application resource as retrieved by
.PN XtDisplayInitialize .
If
selectionTimeout
is not specified,
the default is five seconds.

.NH 3
Using Atomic Transfers
.XS
\*(SN Using Atomic Transfers
.XE
.LP
When using atomic transfers, the owner will completely
process one selection request at a time.
The owner may consider each request individually,
since there is no possibility for overlap
between evaluation of two requests.

.NH 4
Atomic Transfer Procedures
.XS
\*(SN Atomic Transfer Procedures
.XE
.IN "Selections" "atomic"
.LP
The following procedures are used by the selection owner when
providing selection data in a single unit.
.LP
The procedure pointer specified by the owner to supply the selection
data to the \*(xI is of type
.PN XtConvertSelectionProc .
.LP
.IN "XtConvertSelectionProc" "" "@DEF@"
.sM
.FD 0
typedef Boolean (*XtConvertSelectionProc)(Widget, Atom*, Atom*, Atom*,
.br
                      XtPointer*, unsigned long*, int*);
.br
    Widget \fIw\fP;
.br
    Atom *\fIselection\fP;
.br
    Atom *\fItarget\fP;
.br
    Atom *\fItype_return\fP;
.br
    XtPointer *\fIvalue_return\fP;
.br
    unsigned long *\fIlength_return\fP;
.br
    int *\fIformat_return\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that currently owns this selection.
.IP \fIselection\fP 1i
Specifies the atom naming the selection requested
(for example,
.PN XA_PRIMARY
or 
.PN XA_SECONDARY ).
.IP \fItarget\fP 1i
Specifies the target type of the selection that has been requested,
which indicates the desired information about the selection 
(for example, File Name, Text, Window).
.IP \fItype_return\fP 1i
Specifies a pointer to an atom into which the property type of the 
converted value of the selection is to be stored.
For instance, either File Name or Text might have property type 
.PN XA_STRING .
.IP \fIvalue_return\fP 1i
Specifies a pointer into which a pointer to the converted value of the 
selection is to be stored.
The selection owner is responsible for allocating this storage.
If the selection owner has provided an
.PN XtSelectionDoneProc
for the selection, 
this storage is owned by the selection owner; 
otherwise, it is owned by the \*(xI selection mechanism, 
which frees it by calling
.PN XtFree
when it is done with it.
.IP \fIlength_return\fP 1i
Specifies a pointer into which the number of elements in \fIvalue_return\fP,
each of size indicated by \fIformat_return\fP, is to be stored.
.IP \fIformat_return\fP 1i
Specifies a pointer into which the size in bits of the data elements 
of the selection value is to be stored.
.LP
.eM
This procedure is called by the \*(xI selection mechanism 
to get the value of a selection as a given type 
from the current selection owner.
It returns 
.PN True 
if the owner successfully converted the selection to the target type or
.PN False
otherwise.
If the procedure returns
.PN False ,
the values of the return arguments are undefined.
Each
.PN XtConvertSelectionProc
should respond to target value
.PN TARGETS 
by returning a value containing the list of the targets
into which it is
prepared to convert the selection.
The value returned in
\fIformat_return\fP must be one of 8, 16, or 32 to allow the server to
byte-swap the data if necessary.
.LP
.IN "Selections" "MULTIPLE"
.IN "Selections" "TIMESTAMP"
This procedure does not need to worry about responding to the
MULTIPLE or the TIMESTAMP target values (see Section 2.6.2 in the \fI\*(xC\fP).
A selection request with
the MULTIPLE target type is transparently transformed into a
series of calls to this procedure, one for each target type, and a
selection request with the TIMESTAMP target value is answered
automatically by the \*(xI using the time specified in the
call to
.PN XtOwnSelection
or
.PN XtOwnSelectionIncremental .
.sp
.LP
To retrieve the
.PN SelectionRequest
event that triggered the
.PN XtConvertSelectionProc
procedure, use
.PN XtGetSelectionRequest .
.LP
.IN "XtGetSelectionRequest" "" "@DEF@"
.sM
.FD 0
XSelectionRequestEvent *XtGetSelectionRequest(\fIw\fP, \fIselection\fP, \
\fIrequest_id\fP)
.br
      Widget \fIw\fP;
.br
      Atom \fIselection\fP;
.br
      XtRequestId \fIrequest_id\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that currently owns this selection.  \*(cI
.IP \fIselection\fP 1i
Specifies the selection being processed.
.IP \fIrequest_id\fP 1i
Specifies the requestor id in the case of incremental
selections, or NULL in the case of atomic transfers.
.LP
.eM
.PN XtGetSelectionRequest
may be called only from within an
.PN XtConvertSelectionProc
procedure and returns a pointer to the
.PN SelectionRequest
event that caused the conversion procedure to be invoked.
\fIRequest_id\fP specifies a unique id for the individual request in the
case that multiple incremental transfers are outstanding.  For atomic
transfers, \fIrequest_id\fP must be specified as NULL.  If no
.PN SelectionRequest
event is being processed for the specified
\fIwidget\fP, \fIselection\fP, and \fIrequest_id\fP,
.PN XtGetSelectionRequest
returns NULL.
.sp
.LP
The procedure pointer specified by the owner when it desires
notification upon losing ownership is of type
.PN XtLoseSelectionProc .
.LP
.IN "XtLoseSelectionProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtLoseSelectionProc)(Widget, Atom*);
.br
    Widget \fIw\fP;
.br
    Atom *\fIselection\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that has lost selection ownership.
.IP \fIselection\fP 1i
Specifies the atom naming the selection.
.LP
.eM
This procedure is called by the \*(xI selection mechanism
to inform the specified widget that it has lost the given selection.
Note that this procedure does not ask the widget to relinquish the 
selection ownership; it is merely informative.
.sp
.LP
The procedure pointer specified by the owner when it desires
notification of receipt of the data or when it manages the storage
containing the data is of type
.PN XtSelectionDoneProc .
.LP
.IN "XtSelectionDoneProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtSelectionDoneProc)(Widget, Atom*, Atom*);
.br
      Widget \fIw\fP;
.br
      Atom *\fIselection\fP;
.br
      Atom *\fItarget\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that owns the converted selection.
.IP \fIselection\fP 1i
Specifies the atom naming the selection that was converted.
.IP \fItarget\fP 1i
Specifies the target type to which the conversion was done.
.LP
.eM
This procedure is called by the \*(xI selection mechanism
to inform the selection owner that a selection requestor has successfully
retrieved a selection value.
If the selection owner has registered an
.PN XtSelectionDoneProc ,
it should expect it to be called once for each conversion that it performs,
after the converted value has been successfully transferred
to the requestor.
If the selection owner has registered an
.PN XtSelectionDoneProc ,
it also owns the storage containing the converted
selection value.

.NH 4
Getting the Selection Value
.XS
\*(SN Getting the Selection Value
.XE
.LP
The procedure pointer specified by the requestor to receive the
selection data from the \*(xI is of type
.PN XtSelectionCallbackProc .
.LP
.IN "XtSelectionCallbackProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtSelectionCallbackProc)(Widget, XtPointer, Atom*, Atom*, \
XtPointer, unsigned long*, int*);
.br
      Widget \fIw\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      Atom *\fIselection\fP;
.br
      Atom *\fItype\fP;
.br
      XtPointer \fIvalue\fP;
.br
      unsigned long *\fIlength\fP;
.br
      int *\fIformat\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that requested the selection value.
.IP \fIclient_data\fP 1i
Specifies a value passed in by the widget when it requested the
selection.
.IP \fIselection\fP 1i
Specifies the name of the selection that was requested.
.IP \fItype\fP 1i
Specifies the representation type of the selection value (for example,
.PN XA_STRING ).
Note that it is not the target that was requested (which the client
must remember for itself), but the type that
is used to represent the target.
The special symbolic constant
.PN XT_CONVERT_FAIL 
is used to indicate that the selection conversion failed because the
selection owner did not respond within the \*(xI selection timeout
interval.
.IP \fIvalue\fP 1i
Specifies a pointer to the selection value.
The requesting client owns this storage and is responsible for freeing it 
by calling
.PN XtFree
when it is done with it.
.IP \fIlength\fP 1i
Specifies the number of elements in \fIvalue\fP.
.IP \fIformat\fP 1i
Specifies the size in bits of the data in each element of \fIvalue\fP.
.LP
.eM
This procedure is called by the \*(xI selection mechanism to deliver the
requested selection to the requestor.
.LP
If the
.PN SelectionNotify
event returns a property of
.PN None ,
meaning the conversion has been refused because there is no owner for the
specified selection or the owner cannot convert the selection to the
requested target for any reason, the procedure is called with a value
of NULL and a length of zero.
.sp
.LP
To obtain the selection value in a single logical unit, use
.PN XtGetSelectionValue
or
.PN XtGetSelectionValues .
.LP
.IN "XtGetSelectionValue" "" "@DEF@"
.sM
.FD 0
void XtGetSelectionValue(\fIw\fP, \fIselection\fP, \fItarget\fP, \
\fIcallback\fP, \fIclient_data\fP, \fItime\fP)
.br
      Widget \fIw\fP;
.br
      Atom \fIselection\fP;
.br
      Atom \fItarget\fP;
.br
      XtSelectionCallbackProc \fIcallback\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      Time \fItime\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget making the request.  \*(cI
.IP \fIselection\fP 1i
Specifies the particular selection desired; for example,
.PN XA_PRIMARY .
.IP \fItarget\fP 1i
Specifies the type of information needed about the selection.
.IP \fIcallback\fP 1i
Specifies the procedure to be called when the selection value
has been obtained.
Note that this is how the selection value is communicated back to the client.
.IP \fIclient_data\fP 1i
Specifies additional data to be passed to the specified procedure
when it is called.
.IP \fItime\fP 1i
Specifies the timestamp that indicates when the selection request was
initiated.
This should be the timestamp of the event that triggered this request;
the value 
.PN CurrentTime 
is not acceptable.
.LP
.eM
The
.PN XtGetSelectionValue
function requests the value of the selection converted to 
the target type. 
The specified callback is called at some time after 
.PN XtGetSelectionValue 
is called, when the selection value is received from the X server.
It may be called before or after 
.PN XtGetSelectionValue 
returns.
For more information about \fIselection\fP, \fItarget\fP, and
\fItime\fP, see Section 2.6 in the \fI\*(xC\fP.
.sp
.LP
.IN "XtGetSelectionValues" "" "@DEF@"
.sM
.FD 0
void XtGetSelectionValues(\fIw\fP, \fIselection\fP, \fItargets\fP, \
\fIcount\fP, \fIcallback\fP, \fIclient_data\fP, \fItime\fP)
.br
      Widget \fIw\fP;
.br
      Atom \fIselection\fP;
.br
      Atom *\fItargets\fP;
.br
      int \fIcount\fP;
.br
      XtSelectionCallbackProc \fIcallback\fP;
.br
      XtPointer *\fIclient_data\fP;
.br
      Time \fItime\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget making the request.  \*(cI
.IP \fIselection\fP 1i
Specifies the particular selection desired (that is, primary or secondary).
.IP \fItargets\fP 1i
Specifies the types of information needed about the selection.
.IP \fIcount\fP 1i
Specifies the length of the \fItargets\fP and \fIclient_data\fP lists.
.IP \fIcallback\fP 1i
Specifies the callback procedure
to be called with each selection value obtained.
Note that this is how the selection values are communicated back to the
client.
.IP \fIclient_data\fP 1i
Specifies a list of additional data values, one for each target type,
that are passed to the callback procedure when it is called for that target.
.IP \fItime\fP 1i
Specifies the timestamp that indicates when the selection request was
initiated.
This should be the timestamp of the event that triggered this request;
the value 
.PN CurrentTime
is not acceptable.
.LP
.eM
The
.PN XtGetSelectionValues
function is similar to multiple calls to
.PN XtGetSelectionValue 
except that it guarantees that no other client can assert ownership
between requests and therefore that all the conversions will refer to
the same selection value.  The callback is invoked once for each
target value with the corresponding client data.
For more information about \fIselection\fP, \fItarget\fP, and
\fItime\fP, see Section 2.6 in the \fI\*(xC\fP.

.NH 4
Setting the Selection Owner
.XS
\*(SN Setting the Selection Owner
.XE
.LP
To set the selection owner and indicate that the selection value will
be provided in one piece, use
.PN XtOwnSelection .
.LP
.IN "XtOwnSelection" "" "@DEF@"
.sM
.FD 0
Boolean XtOwnSelection(\fIw\fP, \fIselection\fP, \fItime\fP, \
\fIconvert_proc\fP, \fIlose_selection\fP, \fIdone_proc\fP)
.br
      Widget \fIw\fP;
.br
      Atom \fIselection\fP;
.br
      Time \fItime\fP;
.br
      XtConvertSelectionProc \fIconvert_proc\fP;
.br
      XtLoseSelectionProc \fIlose_selection\fP;
.br
      XtSelectionDoneProc \fIdone_proc\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that wishes to become the owner.  \*(cI
.IP \fIselection\fP 1i
Specifies the name of the selection (for example,
.PN XA_PRIMARY ).
.IP \fItime\fP 1i
Specifies the timestamp that indicates when the ownership request was
initiated.
This should be the timestamp of the event that triggered ownership;
the value
.PN CurrentTime 
is not acceptable.
.IP \fIconvert_proc\fP 1i
Specifies the procedure to be called whenever a client requests the 
current value of the selection.
.IP \fIlose_selection\fP 1i
Specifies the procedure to be called whenever the widget has 
lost selection ownership, or NULL if the owner is not interested in being 
called back.
.IP \fIdone_proc\fP 1i
Specifies the procedure called 
after the requestor has received the selection value, or NULL if the
owner is not
interested in being called back.
.LP
.eM
The
.PN XtOwnSelection
function informs the \*(xI selection mechanism that a
widget wishes to own a selection.
It returns 
.PN True 
if the widget successfully becomes the owner and 
.PN False
otherwise.
The widget may fail to become the owner if some other widget 
has asserted ownership at a time later than this widget.
The widget can lose selection ownership either 
because some other widget asserted later ownership of the selection 
or because the widget voluntarily gave up ownership of the selection.
The lose_selection procedure is not called 
if the widget fails to obtain selection ownership in the first place.
.LP
If a done_proc is specified, the client owns the storage allocated
for passing the value to the \*(xI.  If \fIdone_proc\fP is NULL,
the convert_proc must allocate storage using
.PN XtMalloc ,
.PN XtRealloc ,
or
.PN XtCalloc ,
and the value specified is freed by the
\*(xI when the transfer is complete.
.sp
.LP
Usually, a selection owner maintains ownership indefinitely until some
other widget requests ownership, at which time
the \*(xI selection mechanism informs the previous owner that it
has lost ownership of the selection.
However, in response to some user actions 
(for example, when a user deletes the information selected),
the application may wish to explicitly inform the \*(xI
by using
.PN XtDisownSelection
that it no longer is to be the selection owner.
.LP
.IN "XtDisownSelection" "" "@DEF@"
.sM
.FD 0
void XtDisownSelection(\fIw\fP, \fIselection\fP, \fItime\fP)
.br
      Widget \fIw\fP;
.br
      Atom \fIselection\fP;
.br
      Time \fItime\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that wishes to relinquish ownership.
.IP \fIselection\fP 1i
Specifies the atom naming the selection being given up.
.IP \fItime\fP 1i
Specifies the timestamp that indicates when the request to
relinquish selection ownership was initiated.
.LP
.eM
The
.PN XtDisownSelection
function informs the \*(xI selection mechanism that
the specified widget is to lose ownership of the selection.
If the widget does not currently own the selection, either 
because it lost the selection 
or because it never had the selection to begin with,
.PN XtDisownSelection
does nothing.
.LP
After a widget has called
.PN XtDisownSelection ,
its convert procedure is not called even if a request arrives later 
with a timestamp during the period that this widget owned the selection.
However, its done procedure is called if a conversion that started 
before the call to
.PN XtDisownSelection
finishes after the call to
.PN XtDisownSelection .

.NH 3
Using Incremental Transfers
.XS
\*(SN Using Incremental Transfers
.XE
.LP
When using the incremental interface, an owner may have to process
more than one selection request for the same selection, converted to
the same target, at the same time.  The incremental functions take a
\fIrequest_id\fP argument, which is an identifier that is guaranteed to be
unique among all incremental requests that are active concurrently.
.LP
For example, consider the following:
.IP \(bu 5
Upon receiving a request for the selection value, the owner sends
the first segment.
.IP \(bu 5
While waiting to be called to provide the next segment value but
before sending it, the owner receives another request from a
different requestor for the same selection value. 
.IP \(bu 5
To distinguish between the requests, the owner uses the request_id
value.  This allows the owner to distinguish between the first
requestor, which is asking for the second segment, and the second
requestor, which is asking for the first segment. 

.NH 4
Incremental Transfer Procedures
.XS
\*(SN Incremental Transfer Procedures
.XE
.IN "Selections" "incremental"
.LP
The following procedures are used by selection owners who wish to
provide the selection data in multiple segments.
.LP
The procedure pointer specified by the incremental owner to supply the
selection data to the \*(xI is of type
.PN XtConvertSelectionIncrProc .
.LP
.sM
.Ds 0
typedef XtPointer XtRequestId;
.De
.IN "XtRequestId" "" "@DEF@"
.IN "XtConvertSelectionIncrProc" "" "@DEF@"
.FD 0
typedef Boolean (*XtConvertSelectionIncrProc)(Widget, Atom*, Atom*, \
Atom*, XtPointer*,
                               unsigned long*, int*, unsigned long*, \
XtPointer, XtRequestId*);
.br
      Widget \fIw\fP;
.br
      Atom *\fIselection\fP;
.br
      Atom *\fItarget\fP;
.br
      Atom *\fItype_return\fP;
.br
      XtPointer *\fIvalue_return\fP;
.br
      unsigned long *\fIlength_return\fP;
.br
      int *\fIformat_return\fP;
.br
      unsigned long *\fImax_length\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      XtRequestId *\fIrequest_id\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that currently owns this selection.
.IP \fIselection\fP 1i
Specifies the atom that names the selection requested.
.IP \fItarget\fP 1i
Specifies the type of information required about the selection.
.IP \fItype_return\fP 1i
Specifies a pointer to an atom into which the property
type of the converted value of the selection is to be
stored.
.IP \fIvalue_return\fP 1i
Specifies a pointer into which a pointer to the
converted value of the selection is to be stored.
The selection owner is responsible for allocating this storage.
.IP \fIlength_return\fP 1i
Specifies a pointer into which the number of elements
in \fIvalue_return\fP, each of size indicated by
\fIformat_return\fP, is to be stored.
.IP \fIformat_return\fP 1i
Specifies a pointer into which the size in bits of the
data elements of the selection value is to be stored so that the
server may byte-swap the data if necessary.
.IP \fImax_length\fP 1i
Specifies the maximum number of bytes which may be
transferred at any one time.
.IP \fIclient_data\fP 1i
Specifies the value passed in by the widget when it
took ownership of the selection.
.IP \fIrequest_id\fP 1i
Specifies an opaque identification for a specific request.
.LP
.eM
This procedure is called repeatedly by the \*(xI selection mechanism to get
the next incremental chunk of data from a selection owner who has
called
.PN XtOwnSelectionIncremental .
It must return
.PN True
if the procedure has succeeded in converting the selection data or
.PN False
otherwise.
On the first call with a particular request id, the owner must begin
a new incremental transfer for the requested selection and target.  On
subsequent calls with the same request id, the owner may assume that
the previously supplied value is no longer needed by the \*(xI;
that is, a fixed transfer area may be allocated and returned in \fIvalue_return\fP
for each segment to be transferred.  This procedure should store a
non-NULL value in \fIvalue_return\fP and zero in \fIlength_return\fP to indicate that the
entire selection has been delivered.  After returning this final
segment, the request id may be reused by the \*(xI to begin a
new transfer.
.LP
To retrieve the
.PN SelectionRequest
event that triggered the selection conversion procedure, use
.PN XtGetSelectionRequest ,
described in Section 11.5.2.1.
.sp
.LP
The procedure pointer specified by the incremental selection owner
when it desires notification upon no longer having ownership is of
type
.PN XtLoseSelectionIncrProc .
.LP
.IN "XtLoseSelectionIncrProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtLoseSelectionIncrProc)(Widget, Atom*, XtPointer);
.br
      Widget \fIw\fP;
.br
      Atom *\fIselection\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that has lost the selection ownership.
.IP \fIselection\fP 1i
Specifies the atom that names the selection.
.IP \fIclient_data\fP 1i
Specifies the value passed in by the widget when it
took ownership of the selection.
.LP
.eM
This procedure, which is optional, is called by the \*(xI to
inform the selection owner that it no longer owns the selection.
.sp
.LP
The procedure pointer specified by the incremental selection owner
when it desires notification of receipt of the data or when it manages
the storage containing the data is of type
.PN XtSelectionDoneIncrProc .
.LP
.IN "XtSelectionDoneIncrProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtSelectionDoneIncrProc)(Widget, Atom*, Atom*, \
XtRequestId*, XtPointer);
.br
      Widget \fIw\fP;
.br
      Atom *\fIselection\fP;
.br
      Atom *\fItarget\fP;
.br
      XtRequestId *\fIrequest_id\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that owns the selection.
.IP \fIselection\fP 1i
Specifies the atom that names the selection being transferred.
.IP \fItarget\fP 1i
Specifies the target type to which the conversion was done.
.IP \fIrequest_id\fP 1i
Specifies an opaque identification for a specific request.
.IP \fIclient_data\fP 1i
Specified the value passed in by the widget when it
took ownership of the selection.
.LP
.eM
This procedure, which is optional, is called by the \*(xI after
the requestor has retrieved the final (zero-length) segment of the
incremental transfer to indicate that the entire transfer is complete.
If this procedure is not specified, the \*(xI will free only the
final value returned by the selection owner using
.PN XtFree .
.sp
.LP
The procedure pointer specified by the incremental selection owner to
notify it if a transfer should be terminated prematurely is of type
.PN XtCancelConvertSelectionProc .
.LP
.IN "XtCancelConvertSelectionProc" "" "@DEF@"
.sM
.FD 0
typedef void (*XtCancelConvertSelectionProc)(Widget, Atom*, Atom*, \
XtRequestId*, XtPointer);
.br
      Widget \fIw\fP;
.br
      Atom *\fIselection\fP;
.br
      Atom *\fItarget\fP;
.br
      XtRequestId *\fIrequest_id\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget that owns the selection.
.IP \fIselection\fP 1i
Specifies the atom that names the selection being transferred.
.IP \fItarget\fP 1i
Specifies the target type to which the conversion was done.
.IP \fIrequest_id\fP 1i
Specifies an opaque identification for a specific request.
.IP \fIclient_data\fP 1i
Specifies the value passed in by the widget when it took ownership of
the selection.
.LP
.eM
This procedure is called by the \*(xI when it has been determined
by means of a timeout or other mechanism that any remaining segments
of the selection no longer need to be transferred.  Upon receiving
this callback, the selection request is considered complete and the
owner can free the memory and any other resources that have been
allocated for the transfer.

.NH 4
Getting the Selection Value Incrementally
.XS
\*(SN Getting the Selection Value Incrementally
.XE
.LP
To obtain the value of the selection using incremental transfers, use
.PN XtGetSelectionValueIncremental
or
.PN XtGetSelectionValuesIncremental .
.LP
.IN "XtGetSelectionValueIncremental" "" "@DEF@"
.sM
.FD 0
void XtGetSelectionValueIncremental(\fIw\fP, \fIselection\fP, \fItarget\fP, \
\fIselection_callback\fP, \fIclient_data\fP, \fItime\fP)
.br
      Widget \fIw\fP;
.br
      Atom \fIselection\fP;
.br
      Atom \fItarget\fP;
.br
      XtSelectionCallbackProc \fIselection_callback\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      Time \fItime\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget making the request.  \*(cI
.IP \fIselection\fP 1i
Specifies the particular selection desired.
.IP \fItarget\fP 1i
Specifies the type of information needed
about the selection.
.IP \fIselection_callback\fP 1i
Specifies the callback procedure to be
called to receive each data segment.
.IP \fIclient_data\fP 1i
Specifies client-specific data to be passed to
the specified callback procedure when it is invoked.
.IP \fItime\fP 1i
Specifies the timestamp that indicates when the
selection request was initiated.  This should be the
timestamp of the event that triggered this request;
the value
.PN CurrentTime
is not acceptable.
.LP
.eM
The
.PN XtGetSelectionValueIncremental
function is similar to
.PN XtGetSelectionValue
except that the selection_callback procedure will
be called repeatedly upon delivery of multiple segments of the
selection value.  The end of the selection value is indicated when
\fIselection_callback\fP is called with a non-NULL value of length zero,
which must still be freed by the client.  If the
transfer of the selection is aborted in the middle of a transfer
(for example, because of a timeout), the selection_callback procedure is
called with a type value equal to the symbolic constant
.PN XT_CONVERT_FAIL
so that the requestor can dispose
of the partial selection value it has collected up until that point.
Upon receiving
.PN XT_CONVERT_FAIL ,
the requesting client must determine
for itself whether or not a partially completed data transfer is meaningful.
For more information about \fIselection\fP, \fItarget\fP, and
\fItime\fP, see Section 2.6 in the \fI\*(xC\fP.
.LP
.IN "XtGetSelectionValuesIncremental" "" "@DEF@"
.sM
.FD 0
void XtGetSelectionValuesIncremental(\fIw\fP, \fIselection\fP, \fItargets\fP, \
\fIcount\fP, \fIselection_callback\fP, \fIclient_data\fP, \fItime\fP)
.br
      Widget \fIw\fP;
.br
      Atom \fIselection\fP;
.br
      Atom *\fItargets\fP;
.br
      int \fIcount\fP;
.br
      XtSelectionCallbackProc \fIselection_callback\fP;
.br
      XtPointer *\fIclient_data\fP;
.br
      Time \fItime\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget making the request.  \*(cI
.IP \fIselection\fP 1i
Specifies the particular selection desired.
.IP \fItargets\fP 1i
Specifies the types of information needed about
the selection.
.IP \fIcount\fP 1i
Specifies the length of the \fItargets\fP and \fIclient_data\fP lists.
.IP \fIselection_callback\fP 1i
Specifies the callback procedure to be called
to receive each selection value.
.IP \fIclient_data\fP 1i
Specifies a list of client data (one for each target
type) values that are passed to the callback procedure when
it is invoked for the corresponding target.
.IP \fItime\fP 1i
Specifies the timestamp that indicates when the
selection request was initiated.  This should be the
timestamp of the event that triggered this request;
the value
.PN CurrentTime
is not acceptable.
.LP
.eM
The
.PN XtGetSelectionValuesIncremental
function is similar to
.PN XtGetSelectionValueIncremental
except that it takes a list of targets and client data.
.PN XtGetSelectionValuesIncremental
is equivalent to calling
.PN XtGetSelectionValueIncremental
successively for each \fItarget/client_data\fP pair except that
.PN XtGetSelectionValuesIncremental
does guarantee that all the conversions will use the same selection
value because the ownership of the selection cannot change in the
middle of the list, as would be possible when calling
.PN XtGetSelectionValueIncremental
repeatedly.
For more information about \fIselection\fP, \fItarget\fP, and
\fItime\fP, see Section 2.6 in the \fI\*(xC\fP.

.NH 4
Setting the Selection Owner for Incremental Transfers
.XS
\*(SN Setting the Selection Owner for Incremental Transfers
.XE
.LP
To set the selection owner when using incremental transfers, use
.PN XtOwnSelectionIncremental .
.LP
.IN "XtOwnSelectionIncremental" "" "@DEF@"
.sM
.FD 0
Boolean XtOwnSelectionIncremental(\fIw\fP, \fIselection\fP, \fItime\fP, \
\fIconvert_callback\fP, \fIlose_callback\fP,
                                  \fIdone_callback\fP, \
\fIcancel_callback\fP, \fIclient_data\fP)
.br
      Widget \fIw\fP;
.br
      Atom \fIselection\fP;
.br
      Time \fItime\fP;
.br
      XtConvertSelectionIncrProc \fIconvert_callback\fP;
.br
      XtLoseSelectionIncrProc \fIlose_callback\fP;
.br
      XtSelectionDoneIncrProc \fIdone_callback\fP;
.br
      XtCancelConvertSelectionProc \fIcancel_callback\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIw\fP 1.25i
Specifies the widget that wishes to become the owner.  \*(cI
.IP \fIselection\fP 1.25i
Specifies the atom that names the selection.
.IP \fItime\fP 1.25i
Specifies the timestamp that indicates when the
selection ownership request was initiated.  This should be
the timestamp of the event that triggered ownership; the value
.PN CurrentTime
is not acceptable.
.IP \fIconvert_callback\fP 1.25i
Specifies the procedure to be called whenever
the current value of the selection is requested.
.IP \fIlose_callback\fP 1.25i
Specifies the procedure to be called whenever
the widget has lost selection ownership, or NULL if the
owner is not interested in being notified.
.IP \fIdone_callback\fP 1.25i
Specifies the procedure called after the
requestor has received the entire selection, or NULL if
the owner is not interested in being notified.
.IP \fIcancel_callback\fP 1.25i
Specifies the callback procedure to be called
when a selection request aborts because a timeout expires,
or NULL if the owner is not interested in being notified.
.IP \fIclient_data\fP 1.25i
Specifies the argument to be passed to each of
the callback procedures when they are called.
.LP
.eM
The
.PN XtOwnSelectionIncremental
procedure informs the \*(xI
incremental selection mechanism that the specified widget wishes to
own the selection.  It returns
.PN True
if the specified widget successfully becomes the selection owner or
.PN False
otherwise.
For more information about \fIselection\fP, \fItarget\fP, and
\fItime\fP, see Section 2.6 in the \fI\*(xC\fP.
.LP
If a done_callback procedure is specified, the client owns the storage allocated
for passing the value to the \*(xI.  If \fIdone_callback\fP is NULL,
the convert_callback procedure must allocate storage using
.PN XtMalloc ,
.PN XtRealloc ,
or
.PN XtCalloc ,
and the final value specified is freed by the
\*(xI when the transfer is complete.  After a selection transfer
has started, only one of the done_callback or cancel_callback
procedures is invoked to indicate completion of the transfer.
.LP
The lose_callback procedure does not indicate completion of any in-progress
transfers; it is invoked at the time a
.PN SelectionClear
event is dispatched regardless of any active transfers, which are still
expected to continue.
.LP
A widget that becomes the selection owner using
.PN XtOwnSelectionIncremental
may use
.PN XtDisownSelection
to relinquish selection ownership.

.NH 3
Setting and Retrieving Selection Target Parameters
.XS
\*(SN Setting and Retrieving Selection Target Parameters
.XE
.LP
To specify target parameters for a selection request with a single target,
use
.PN XtSetSelectionParameters .
.LP
.IN "XtSetSelectionParameters" "" "@DEF@"
.sM
.FD 0
void XtSetSelectionParameters(\fIrequestor\fP, \fIselection\fP, \fItype\fP, \
\fIvalue\fP, \fIlength\fP, \fIformat\fP)
.br
      Widget \fIrequestor\fP;
.br
      Atom \fIselection\fP;
.br
      Atom \fItype\fP;
.br
      XtPointer \fIvalue\fP;
.br
      unsigned long \fIlength\fP;
.br
      int \fIformat\fP;
.FN
.IP \fIrequestor\fP 1i
Specifies the widget making the request.  \*(cI
.IP \fIselection\fP 1i
Specifies the atom that names the selection.
.IP \fItype\fP 1i
Specifies the type of the property in which the parameters are passed.
.IP \fIvalue\fP 1i
Specifies a pointer to the parameters.
.IP \fIlength\fP 1i
Specifies the number of elements containing data in \fIvalue\fP,
each element of a size indicated by \fIformat\fP.
.IP \fIformat\fP 1i
Specifies the size in bits of the data in the elements of \fIvalue\fP.
.LP
The specified parameters are copied and stored in a new property 
of the specified type and format on the requestor's window.  To initiate
a selection request with a target and these parameters, a subsequent
call to 
.PN XtGetSelectionValue
or to
.PN XtGetSelectionValueIncremental
specifying the same requestor widget and selection atom will generate a
.PN ConvertSelection
request referring to the property containing the parameters.  If 
.PN XtSetSelectionParameters
is called more than once with the same widget and selection without
a call to specify a request, the most recently specified parameters
are used in the subsequent request.
.LP
.eM
The possible values of \fIformat\fP are 8, 16, or 32.  If the format is 8,
the elements of \fIvalue\fP are assumed to be sizeof(char);
if 16, sizeof(short); if 32, sizeof(long).
.LP
To generate a MULTIPLE
target request with parameters for any of the multiple targets of the
selection request, precede individual calls to
.PN XtGetSelectionValue
and
.PN XtGetSelectionValueIncremental
with corresponding individual calls to
.PN XtSetSelectionParameters ,
and enclose these all within 
.PN XtCreateSelectionRequest
and
.PN XtSendSelectionRequest.  
.PN XtGetSelectionValues
and
.PN XtGetSelectionValuesIncremental
cannot be used to make selection requests with parameterized targets.
.sp
.LP
To retrieve any target parameters needed to perform a selection conversion,
the selection owner calls 
.PN XtGetSelectionParameters .
.LP
.IN "XtGetSelectionParameters" "" "@DEF@"
.sM
.FD 0
void XtGetSelectionParameters(\fIowner\fP, \fIselection\fP, \
\fIrequest_id\fP, \fItype_return\fP, \fIvalue_return\fP,
                                                 \fIlength_return\fP, \
\fIformat_return\fP)
.br
      Widget \fIowner\fP;
.br
      Atom \fIselection\fP;
.br
      XtRequestId \fIrequest_id\fP;
.br
      Atom *\fItype_return\fP;
.br
      XtPointer *\fIvalue_return\fP;
.br
      unsigned long *\fIlength_return\fP;
.br
      int *\fIformat_return\fP;
.FN
.IP \fIowner\fP 1i
Specifies the widget that owns the specified selection.
.IP \fIselection\fP 1i
Specifies the selection being processed.
.IP \fIrequest_id\fP 1i
Specifies the requestor id in the case of incremental selections,
or NULL in the case of atomic transfers.
.IP \fItype_return\fP 1i
Specifies a pointer to an atom in which the property type
of the parameters is stored.
.IP \fIvalue_return\fP 1i
Specifies a pointer into which a pointer to the parameters is to be stored.
A NULL is stored if no parameters accompany the request.
.IP \fIlength_return\fP 1i
Specifies a pointer into which the number of data elements
in \fIvalue_return\fP of size indicated by \fIformat_return\fP are stored.
.IP \fIformat_return\fP 1i
Specifies a pointer into which the size in bits of the parameter data
in the elements of \fIvalue\fP is stored.
.LP
.eM
.PN XtGetSelectionParameters
may be called only from within an
.PN XtConvertSelectionProc
or from within the first call to an 
.PN XtConvertSelectionIncrProc
with a new request_id.
.LP
It is the responsibility of the caller to free the returned parameters using
.PN XtFree
when the parameters are no longer needed.

.NH 3
Generating MULTIPLE Requests
.XS
\*(SN Generating MULTIPLE Requests
.XE
.LP
To have the \*(xI bundle multiple calls to make selection requests into
a single request using a \s-1MULTIPLE\s+1 target, use 
.PN XtCreateSelectionRequest
and
.PN XtSendSelectionRequest .
.LP
.IN "XtCreateSelectionRequest" "" "@DEF@"
.sM
.FD 0
void XtCreateSelectionRequest(\fIrequestor\fP, \fIselection\fP)
.br
      Widget \fIrequestor\fP;
.br
      Atom \fIselection\fP;
.FN
.IP \fIrequestor\fP 1i
Specifies the widget making the request.  \*(cI
.IP \fIselection\fP 1i
Specifies the particular selection desired.
.LP
.eM
When 
.PN XtCreateSelectionRequest
is called, subsequent calls to 
.PN XtGetSelectionValue ,
.PN XtGetSelectionValueIncremental ,
.PN XtGetSelectionValues ,
and
.PN XtGetSelectionValuesIncremental ,
with the requestor and selection as specified to 
.PN XtCreateSelectionRequest ,
are bundled into a single selection request with
multiple targets.  The request is made by calling 
.PN XtSendSelectionRequest .
.LP
.IN "XtSendSelectionRequest" "" "@DEF@"
.sM
.FD 0
void XtSendSelectionRequest(\fIrequestor\fP, \fIselection\fP, \fItime\fP)
.br
      Widget \fIrequestor\fP;
.br
      Atom \fIselection\fP;
.br
      Time \fItime\fP;
.FN
.IP \fIrequestor\fP 1i
Specifies the widget making the request.  \*(cI
.IP \fIselection\fP 1i
Specifies the particular selection desired.
.IP \fItime\fP 1i
Specifies the timestamp that indicates when the selection request was
initiated.  The value 
.PN CurrentTime
is not acceptable.
.LP
.eM
When 
.PN XtSendSelectionRequest
is called with a value of \fIrequestor\fP and \fIselection\fP matching
a previous call to 
.PN XtCreateSelectionRequest ,
a selection request is sent to the selection owner.
If a single target request is queued, that request is made.
If multiple targets are queued, they are bundled into a single request
with a target of MULTIPLE using the specified timestamp.
As the values are returned, the callbacks specified in
.PN XtGetSelectionValue ,
.PN XtGetSelectionValueIncremental ,
.PN XtGetSelectionValues ,
and
.PN XtGetSelectionValueIncremental
are invoked.
.LP
Multi-threaded applications should lock the application context before
calling
.PN XtCreateSelectionRequest
and release the lock after calling
.PN XtSendSelectionRequest
to ensure that the thread assembling the request is safe from interference
by another thread assembling a different request naming the same widget
and selection.
.sp
.LP
To relinquish the composition of a MULTIPLE request without sending it, use
.PN XtCancelSelectionRequest .
.LP
.IN "XtCancelSelectionRequest" "" "@DEF@"
.sM
.FD 0
void XtCancelSelectionRequest(\fIrequestor\fP, \fIselection\fP)
.br
      Widget \fIrequestor\fP;
.br
      Atom \fIselection\fP;
.FN
.IP \fIrequestor\fP 1i
Specifies the widget making the request.  \*(cI
.IP \fIselection\fP 1i
Specifies the particular selection desired.
.LP
.eM
When
.PN XtCancelSelectionRequest
is called, any requests queued since the last call to
.PN XtCreateSelectionRequest
for the same widget and selection are discarded
and any resources reserved are released.
A subsequent call to
.PN XtSendSelectionRequest
will not result in any request being made.
Subsequent calls to
.PN XtGetSelectionValue ,
.PN XtGetSelectionValues ,
.PN XtGetSelectionValueIncremental ,
or
.PN XtGetSelectionValuesIncremental
will not be deferred.

.NH 3
Auxiliary Selection Properties
.XS
\*(SN Auxiliary Selection Properties
.XE
.LP
Certain uses of parameterized selections require clients to name
other window properties within a selection parameter.  To permit
reuse of temporary property names in these circumstances and
thereby reduce the number of unique atoms created in the server,
the \*(xI provides two interfaces for acquiring temporary property names.
.LP
To acquire a temporary property name atom for use in a selection
request, the client may call
.PN XtReservePropertyAtom .
.LP
.IN "XtReservePropertyAtom" "" "@DEF@"
.sM
.FD 0
Atom XtReservePropertyAtom(\fIw\fP)
.br
      Widget \fIw\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget making a selection request.
.LP
.eM
.PN XtReservePropertyAtom
returns an atom that may be used as a property name during selection
requests involving the specified widget. 
As long as the atom remains reserved, it is unique with respect to all
other reserved atoms for the widget.
.LP
To return a temporary property name atom for reuse and to delete
the property named by that atom, use
.PN XtReleasePropertyAtom .
.LP
.IN "XtReleasePropertyAtom" "" "@DEF@"
.sM
.FD 0
void XtReleasePropertyAtom(\fIw\fP, \fIatom\fP)
.br
      Widget \fIw\fP;
.br
      Atom \fIatom\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget used to reserve the property name atom.
.IP \fIatom\fP 1i
Specifies the property name atom returned by
.PN XtReservePropertyAtom
that is to be released for reuse.
.LP
.eM
.PN XtReleasePropertyAtom
marks the specified property name atom as
no longer in use and ensures that any property having that name
on the specified widget's window is deleted.  If \fIatom\fP does not
specify a value returned by
.PN XtReservePropertyAtom
for the specified widget, the results are undefined.

.NH 3
Retrieving the Most Recent Timestamp
.XS
\*(SN Retrieving the Most Recent Timestamp
.XE
.LP
To retrieve the timestamp from the most recent call to
.PN XtDispatchEvent
that contained a timestamp, use
.PN XtLastTimestampProcessed .
.LP
.IN "XtLastTimestampProcessed" "" "@DEF@"
.sM
.FD 0
Time XtLastTimestampProcessed(\fIdisplay\fP)
.br
      Display *\fIdisplay\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies an open display connection.
.LP
.eM
If no
.PN KeyPress ,
.PN KeyRelease ,
.PN ButtonPress ,
.PN ButtonRelease ,
.PN MotionNotify ,
.PN EnterNotify ,
.PN LeaveNotify ,
.PN PropertyNotify ,
or
.PN SelectionClear
event has yet been passed to
.PN XtDispatchEvent
for the specified display,
.PN XtLastTimestampProcessed
returns zero.

.NH 3
Retrieving the Most Recent Event
.XS
\*(SN Retrieving the Most Recent Event
.XE
.LP
To retrieve the event from the most recent call to
.PN XtDispatchEvent
for a specific display, use
.PN XtLastEventProcessed .
.LP
.IN "XtLastEventProcessed" "" "@DEF@"
.sM
.FD 0
XEvent *XtLastEventProcessed(\fIdisplay\fP)
.br
      Display *\fIdisplay\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies the display connection from which to retrieve the event.
.LP
.eM
Returns the last event passed to
.PN XtDispatchEvent
for the specified display.  Returns NULL if there is no such event.
The client must not modify the contents of the returned event.

.NH 2
Merging Exposure Events into a Region
.XS
\*(SN Merging Exposure Events into a Region
.XE
.LP
The \*(xI provide an
.PN XtAddExposureToRegion
utility function that merges
.PN Expose
and
.PN GraphicsExpose
events into a region for clients to process at once
rather than processing individual rectangles.
For further information about regions,
see Section 16.5 in \fI\*(xL\fP.
.sp
.LP
To merge
.PN Expose
and
.PN GraphicsExpose
events into a region, use
.PN XtAddExposureToRegion .
.LP
.IN "XtAddExposureToRegion" "" "@DEF@"
.sM
.FD 0
void XtAddExposureToRegion(\fIevent\fP, \fIregion\fP)
.br
     XEvent *\fIevent\fP;
.br
     Region \fIregion\fP;
.FN
.IP \fIevent\fP 1i
Specifies a pointer to the
.PN Expose
or
.PN GraphicsExpose
event.
.IP \fIregion\fP 1i
Specifies the region object (as defined in
.Pn < X11/Xutil.h >).
.LP
.eM
The
.PN XtAddExposureToRegion
function computes the union of the rectangle defined by the exposure
event and the specified region.
Then it stores the results back in \fIregion\fP.
If the event argument is not an
.PN Expose
or
.PN GraphicsExpose
event,
.PN XtAddExposureToRegion
returns without an error and without modifying \fIregion\fP.
.LP
This function is used by the exposure compression mechanism;
see Section 7.9.3.

.NH 2
Translating Widget Coordinates
.XS
\fB\*(SN Translating Widget Coordinates\fP
.XE
.LP
To translate an x-y coordinate pair from widget coordinates to root
window absolute coordinates, use
.PN XtTranslateCoords .
.LP
.IN "XtTranslateCoords" "" "@DEF@"
.sM
.FD 0
void XtTranslateCoords(\fIw\fP, \fIx\fP, \fIy\fP, \fIrootx_return\fP, \
\fIrooty_return\fP)
.br
      Widget \fIw\fP;
.br
      Position \fIx\fP, \fIy\fP;
.br
      Position *\fIrootx_return\fP, *\fIrooty_return\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.  \*(rI
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the widget-relative x and y coordinates.
.IP \fIrootx_return\fP 1i
.br
.ns
.IP \fIrooty_return\fP 1i
Return the root-relative x and y coordinates.
.LP
.eM
While
.PN XtTranslateCoords
is similar to the Xlib
.PN XTranslateCoordinates 
function, it does not generate a server request because all the required
information already is in the widget's data structures.

.NH 2
Translating a Window to a Widget
.XS
\fB\*(SN Translating a Window to a Widget\fP
.XE
.LP
To translate a given window and display pointer into a widget instance, use
.PN XtWindowToWidget .
.LP
.IN "XtWindowToWidget" "" "@DEF@"
.sM
.FD 0
Widget XtWindowToWidget(\fIdisplay\fP, \fIwindow\fP)
.br
      Display *\fIdisplay\fP;
.br
      Window \fIwindow\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies the display on which the window is defined.
.IP \fIwindow\fP 1i
Specifies the drawable for which you want the widget.
.LP
.eM
If there is a realized widget whose window is the specified drawable on
the specified \fIdisplay\fP,
.PN XtWindowToWidget
returns that widget.
If not and if the drawable has been associated with a widget through
.PN XtRegisterDrawable ,
.PN XtWindowToWidget
returns the widget associated with the drawable.  In other cases it
returns NULL.

.NH 2
Handling Errors
.XS
\fB\*(SN Handling Errors\fP
.XE
.LP
The \*(xI allow a client to register procedures that are called
whenever a fatal or nonfatal error occurs.
These facilities are intended for both error reporting and logging
and for error correction or recovery.
.LP
Two levels of interface are provided: 
.IP \(bu 5
A high-level interface that takes an error
name and class and retrieves the error message text from
an error resource database.
.IP \(bu 5
A low-level interface that takes a simple string to display.
.LP
The high-level functions construct a string to pass to the lower-level
interface.
The strings may be specified in application code and are
overridden by the contents of an external systemwide file,
the ``error database file''.  The location and name of this file are
implementation-dependent.
.NT
The application-context-specific error handling is not
implemented on many systems, although the interfaces are
always present.
Most implementations will have just one set of error handlers
for all application contexts within a process.
If they are set for different application contexts,
the ones registered last will prevail.
.NE
.sp
.LP
To obtain the error database (for example, to merge with
an application- or widget-specific database), use
.PN XtAppGetErrorDatabase .
.LP
.IN "XtAppGetErrorDatabase" "" "@DEF@"
.sM
.FD 0
XrmDatabase *XtAppGetErrorDatabase(\^\fIapp_context\fP\^)
.br
     XtAppContext \fIapp_context\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.LP
.eM
The
.PN XtAppGetErrorDatabase
function returns the address of the error database.
The \*(xI do a lazy binding of the error database and do not merge in the
database file until the first call to
.PN XtAppGetErrorDatabaseText .
.LP
For a complete listing of all errors and warnings 
that can be generated by the \*(xI, see Appendix D.
.sp
.LP
The high-level error and warning handler procedure pointers are of type
.PN XtErrorMsgHandler .
.LP
.IN "XtErrorMsgHandler" "" "@DEF@"
.sM
.FD 0
typedef void (*XtErrorMsgHandler)(String, String, String, String, \
String*, Cardinal*);
.br
    String \fIname\fP;
.br
    String \fItype\fP;
.br
    String \fIclass\fP;
.br
    String \fIdefaultp\fP;
.br
    String *\fIparams\fP;
.br
    Cardinal *\fInum_params\fP;
.FN
.IP \fIname\fP 1i
Specifies the name to be concatenated with the specified type to form 
the resource name of the error message.
.IP \fItype\fP 1i
Specifies the type to be concatenated with the name to form the 
resource name of the error message.
.IP \fIclass\fP 1i
Specifies the resource class of the error message.
.IP \fIdefaultp\fP 1i
Specifies the default message to use if no error database entry is found.
.IP \fIparams\fP 1i
Specifies a pointer to a list of parameters to be substituted in the message.
.IP \fInum_params\fP 1i
Specifies the number of entries in \fIparams\fP.
.LP
.eM
The specified name can be a general kind of error, 
like ``invalidParameters'' or ``invalidWindow'', 
and the specified type gives extra information
such as the name of the routine in which the error was detected.
Standard 
.PN printf 
notation is used to substitute the parameters into the message.
.sp
.LP
An error message handler can obtain the error database text for an
error or a warning by calling
.PN XtAppGetErrorDatabaseText .
.LP
.IN "XtAppGetErrorDatabaseText" "" "@DEF@"
.sM
.FD 0
void XtAppGetErrorDatabaseText(\fIapp_context\fP, \fIname\fP, \fItype\fP, \fIclass\fP, \fIdefault\fP, \fIbuffer_return\fP, \fInbytes\fP, \fIdatabase\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      String \fIname\fP, \fItype\fP, \fIclass\fP;
.br
      String \fIdefault\fP;
.br
      String \fIbuffer_return\fP;
.br
      int \fInbytes\fP;
.br
      XrmDatabase \fIdatabase\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fIname\fP 1i
.br
.ns
.IP \fItype\fP 1i
Specify the name and type concatenated to form the resource name 
of the error message.
.IP \fIclass\fP 1i
Specifies the resource class of the error message.
.IP \fIdefault\fP 1i
Specifies the default message to use if an error database entry is not found.
.IP \fIbuffer_return\fP 1i
Specifies the buffer into which the error message is to be returned.
.IP \fInbytes\fP 1i
Specifies the size of the buffer in bytes.
.IP \fIdatabase\fP 1i
Specifies the name of the alternative database to be used,
or NULL if the application context's error database is to be used.
.LP
.eM
The
.PN XtAppGetErrorDatabaseText
returns the appropriate message from the error database
or returns the specified default message if one is not found in the
error database.
To form the full resource name and class when querying the database,
the \fIname\fP and \fItype\fP are concatenated with a single ``.''
between them and the \fIclass\fP is concatenated with itself with a
single ``.'' if it does not already contain a ``.''.
.sp
.LP
To return the application name and class as passed to
.PN XtDisplayInitialize
for a particular Display, use
.PN XtGetApplicationNameAndClass .
.LP
.IN "XtGetApplicationNameAndClass" "" "@DEF@"
.sM
.FD 0
void XtGetApplicationNameAndClass(\fIdisplay\fP, \fIname_return\fP, \
\fIclass_return\fP)
.br
      Display* \fIdisplay\fP;
.br
      String* \fIname_return\fP;
.br
      String* \fIclass_return\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies an open display connection that has been initialized with
.PN XtDisplayInitialize .
.IP \fIname_return\fP 1i
Returns the application name.
.IP \fIclass_return\fP 1i
Returns the application class.
.LP
.eM
.PN XtGetApplicationNameAndClass
returns the application name and class passed to
.PN XtDisplayInitialize
for the specified display.  If the display was
never initialized or has been closed, the result is undefined.  The
returned strings are owned by the \*(xI and must not be modified
or freed by the caller.
.sp
.LP
To register a procedure to be called on fatal error conditions, use
.PN XtAppSetErrorMsgHandler .
.LP
.IN "XtAppSetErrorMsgHandler" "" "@DEF@"
.sM
.FD 0
XtErrorMsgHandler XtAppSetErrorMsgHandler(\fIapp_context\fP, \fImsg_handler\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XtErrorMsgHandler \fImsg_handler\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fImsg_handler\fP 1i
Specifies the new fatal error procedure, which should not return.
.LP
.eM
.PN XtAppSetErrorMsgHandler
returns a pointer to the previously
installed high-level fatal error handler.
The default high-level fatal error handler provided by the \*(xI is named
.PN _XtDefaultErrorMsg
.IN "_XtDefaultErrorMsg" "" "@DEF"
and constructs a string from the error resource database and calls
.PN XtError .
Fatal error message handlers should not return.
If one does,
subsequent \*(xI behavior is undefined.
.sp
.LP
To call the high-level error handler, use
.PN XtAppErrorMsg .
.LP
.IN "XtAppErrorMsg" "" "@DEF@"
.sM
.FD 0
void XtAppErrorMsg(\fIapp_context\fP, \fIname\fP, \fItype\fP, \fIclass\fP, \
\fIdefault\fP, \ \fIparams\fP, \fInum_params\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      String \fIname\fP;
.br
      String \fItype\fP;
.br
      String \fIclass\fP;
.br
      String \fIdefault\fP;
.br
      String *\fIparams\fP;
.br
      Cardinal *\fInum_params\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fIname\fP 1i
Specifies the general kind of error.
.IP \fItype\fP 1i
Specifies the detailed name of the error.
.IP \fIclass\fP 1i
Specifies the resource class.
.IP \fIdefault\fP 1i
Specifies the default message to use if an error database entry is not found.
.IP \fIparams\fP 1i
Specifies a pointer to a list of values to be stored in the message.
.IP \fInum_params\fP 1i
Specifies the number of entries in \fIparams\fP.
.LP
.eM
The \*(xI internal errors all have class
``XtToolkitError''.
.sp
.LP
To register a procedure to be called on nonfatal error conditions, use
.PN XtAppSetWarningMsgHandler .
.LP
.IN "XtAppSetWarningMsgHandler" "" "@DEF@"
.sM
.FD 0
XtErrorMsgHandler XtAppSetWarningMsgHandler(\fIapp_context\fP, \fImsg_handler\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XtErrorMsgHandler \fImsg_handler\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fImsg_handler\fP 1i
Specifies the new nonfatal error procedure, which usually returns.
.LP
.eM
.PN XtAppSetWarningMsgHandler
returns a pointer to the previously
installed high-level warning handler.
The default high-level warning handler provided by the \*(xI is named
.PN _XtDefaultWarningMsg
.IN "_XtDefaultWarningMsg" "" "@DEF@"
and constructs a string
from the error resource database and calls
.PN XtWarning .
.sp
.LP
To call the installed high-level warning handler, use
.PN XtAppWarningMsg .
.LP
.IN "XtAppWarningMsg" "" "@DEF@"
.sM
.FD 0
void XtAppWarningMsg(\fIapp_context\fP, \fIname\fP, \fItype\fP, \fIclass\fP, \fIdefault\fP, \fIparams\fP, \fInum_params\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      String \fIname\fP;
.br
      String \fItype\fP;
.br
      String \fIclass\fP;
.br
      String \fIdefault\fP;
.br
      String *\fIparams\fP;
.br
      Cardinal *\fInum_params\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fIname\fP 1i
Specifies the general kind of error.
.IP \fItype\fP 1i
Specifies the detailed name of the error.
.IP \fIclass\fP 1i
Specifies the resource class.
.IP \fIdefault\fP 1i
Specifies the default message to use if an error database entry is not found.
.IP \fIparams\fP 1i
Specifies a pointer to a list of values to be stored in the message.
.IP \fInum_params\fP 1i
Specifies the number of entries in \fIparams\fP.
.LP
.eM
The \*(xI internal warnings all have class
``XtToolkitError''.
.sp
.LP
The low-level error and warning handler procedure pointers are of type
.PN XtErrorHandler .
.LP
.IN "XtErrorHandler" "" "@DEF@"
.sM
.FD 0
typedef void (*XtErrorHandler)(String);
.br
      String \fImessage\fP;
.FN
.IP \fImessage\fP 1i
Specifies the error message.
.LP
.eM
The error handler should display the message string in some appropriate fashion.
.sp
.LP
To register a procedure to be called on fatal error conditions, use
.PN XtAppSetErrorHandler .
.LP
.IN "XtAppSetErrorHandler" "" "@DEF@"
.sM
.FD 0
XtErrorHandler XtAppSetErrorHandler(\fIapp_context\fP, \fIhandler\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XtErrorHandler \fIhandler\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fIhandler\fP 1i
Specifies the new fatal error procedure, which should not return.
.LP
.eM
.PN XtAppSetErrorHandler
returns a pointer to the previously installed
low-level fatal error handler.
The default low-level error handler provided by the \*(xI is
.PN _XtDefaultError .
.IN "_XtDefaultError" "" "@DEF@"
On POSIX-based systems,
it prints the message to standard error and terminates the application.
Fatal error message handlers should not return.
If one does,
subsequent \*(xI behavior is undefined.
.sp
.LP
To call the installed fatal error procedure, use
.PN XtAppError .
.LP
.IN "XtAppError" "" "@DEF@"
.sM
.FD 0
void XtAppError(\fIapp_context\fP, \fImessage\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      String \fImessage\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fImessage\fP 1i
Specifies the message to be reported.
.LP
.eM
Most programs should use
.PN XtAppErrorMsg ,
not
.PN XtAppError ,
to provide for customization and internationalization of error messages.
.sp
.LP
To register a procedure to be called on nonfatal error conditions, use
.PN XtAppSetWarningHandler .
.LP
.IN "XtAppSetWarningHandler" "" "@DEF@"
.sM
.FD 0
XtErrorHandler XtAppSetWarningHandler(\fIapp_context\fP, \fIhandler\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      XtErrorHandler \fIhandler\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fIhandler\fP 1i
Specifies the new nonfatal error procedure, which usually returns.
.LP
.eM
.PN XtAppSetWarningHandler
returns a pointer to the previously installed
low-level warning handler.
The default low-level warning handler provided by the \*(xI is
.PN _XtDefaultWarning .
.IN "_XtDefaultWarning" "" "@DEF@"
On POSIX-based systems,
it prints the message to standard error and returns to the caller.
.sp
.LP
To call the installed nonfatal error procedure, use
.PN XtAppWarning .
.LP
.IN "XtAppWarning" "" "@DEF@"
.sM
.FD 0
void XtAppWarning(\fIapp_context\fP, \fImessage\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      String \fImessage\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context.
.IP \fImessage\fP 1i
Specifies the nonfatal error message to be reported.
.LP
.eM
Most programs should use
.PN XtAppWarningMsg ,
not
.PN XtAppWarning ,
to provide for customization and internationalization of warning messages.

.NH 2
Setting WM_COLORMAP_WINDOWS
.XS
\fB\*(SN Setting WM_COLORMAP_WINDOWS\fP
.XE
.LP
A client may set the value of the \s-1WM_COLORMAP_WINDOWS\s+1
.IN "WM_COLORMAP_WINDOWS" "" "@DEF@"
property on a widget's window by calling
.PN XtSetWMColormapWindows .
.LP
.IN "XtSetWMColormapWindows" "" "@DEF@"
.sM
.FD 0
void XtSetWMColormapWindows(\fIwidget\fP, \fIlist\fP, \fIcount\fP)
.br
      Widget \fIwidget\fP;
.br
      Widget* \fIlist\fP;
.br
      Cardinal \fIcount\fP;
.FN
.IP \fIwidget\fP 1i
Specifies the widget on whose window the \s-1WM_COLORMAP_WINDOWS\s+1
property is stored.  \*(cI
.IP \fIlist\fP 1i
Specifies a list of widgets whose windows are potentially to be
listed in the \s-1WM_COLORMAP_WINDOWS\s+1 property.
.IP \fIcount\fP 1i
Specifies the number of widgets in \fIlist\fP.
.LP
.eM
.PN XtSetWMColormapWindows
returns immediately if \fIwidget\fP is not realized or if \fIcount\fP is 0.
Otherwise,
.PN XtSetWMColormapWindows
constructs an ordered list of windows
by examining each widget in \fIlist\fP in turn and
ignoring the widget if it is not realized, or
adding the widget's window to the window list if the widget is realized
and if its colormap resource is different from the colormap
resources of all widgets whose windows are already on the window list.
.LP
Finally,
.PN XtSetWMColormapWindows
stores the resulting window list in the \s-1WM_COLORMAP_WINDOWS\s+1
property on the specified widget's window.
Refer to Section 4.1.8 in the \fI\*(xC\fP for details of
the semantics of the \s-1WM_COLORMAP_WINDOWS\s+1 property.

.NH 2
Finding File Names
.XS
\fB\*(SN Finding File Names\fP
.XE
.LP
The \*(xI provide procedures to look for a file by name, allowing
string substitutions in a list of file specifications.  Two
routines are provided for this:
.PN XtFindFile
and
.PN XtResolvePathname .
.PN XtFindFile
uses an arbitrary set of client-specified substitutions, and
.PN XtResolvePathname
uses a set of standard substitutions corresponding
to the \fIX/Open Portability Guide\fP language localization conventions.
Most applications should use
.PN XtResolvePathname .
.LP
A string substitution is defined by a list of
.PN Substitution
.IN "Substitution" "" "@DEF@"
entries.
.LP
.sM
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	char match;
	String substitution;
} SubstitutionRec, *Substitution;
.De
.eM
.LP
File name evaluation is handled in an operating-system-dependent
fashion by an
.PN XtFilePredicate
.IN "XtFilePredicate" "" "@DEF@"
procedure.
.LP
.sM
.FD 0
typedef Boolean (*XtFilePredicate)(String);
.br
      String \fIfilename\fP;
.FN
.IP \fIfilename\fP 1i
Specifies a potential filename.
.LP
.eM
A file predicate procedure is called with a string that is
potentially a file name.  It should return
.PN True 
if this string specifies a file that is appropriate for the intended use and 
.PN False
otherwise.
.sp
.LP
To search for a file using substitutions in a path list, use
.PN XtFindFile .
.LP
.IN "XtFindFile" "" "@DEF@"
.sM
.FD 0
String XtFindFile(\fIpath\fP, \fIsubstitutions\fP, \fInum_substitutions\fP, \
\fIpredicate\fP)
.br
      String \fIpath\fP;
.br
      Substitution \fIsubstitutions\fP;
.br
      Cardinal \fInum_substitutions\fP;
.br
      XtFilePredicate \fIpredicate\fP;
.FN
.IP \fIpath\fP 1.2i
Specifies a path of file names, including substitution characters.
.IP \fIsubstitutions\fP 1.2i
Specifies a list of substitutions to make into the path.
.IP \fInum_substitutions\fP 1.2i
Specifies the number of substitutions passed in.
.IP \fIpredicate\fP 1.2i
Specifies a procedure called to judge each potential file name, or NULL.
.LP
.eM
The \fIpath\fP parameter specifies a string that consists of a series of
potential file names delimited by colons.  Within each name, the
percent character specifies a string substitution selected by the
following character.  The character sequence ``%:'' specifies an
embedded colon that is not a delimiter; the sequence is replaced by a
single colon.  The character sequence ``%%'' specifies a percent
character that does not introduce a substitution; the sequence is
replaced by a single percent character.  If a percent character is
followed by any other character,
.PN XtFindFile
looks through the
specified \fIsubstitutions\fP for that character in the \fImatch\fP field
and, if found,
replaces the percent and match characters with the string in the
corresponding \fIsubstitution\fP field.  A \fIsubstitution\fP field entry of NULL
is equivalent to a pointer to an empty string.  If the operating
system does not interpret multiple embedded name separators in the
path (i.e., ``/'' in POSIX) the same way as a single separator,
.PN XtFindFile
will collapse multiple separators into a single one after performing
all string substitutions.  Except for collapsing embedded separators,
the contents of the string substitutions are not interpreted by
.PN XtFindFile
and may therefore contain any operating-system-dependent
characters, including additional name separators.  Each resulting
string is passed to the predicate procedure until a string is found for
which the procedure returns
.PN True ;
this string is the return value for
.PN XtFindFile .
If no string yields a
.PN True
return from the predicate,
.PN XtFindFile
returns NULL.
.LP
If the \fIpredicate\fP parameter is NULL, an internal procedure that checks
if the file exists, is readable, and is not a directory is used.
.LP
It is the responsibility of the caller to free the returned string using
.PN XtFree
when it is no longer needed.
.sp
.LP
To search for a file using standard substitutions in a path list, use
.PN XtResolvePathname .
.LP
.IN "XtResolvePathname" "" "@DEF@"
.sM
.FD 0
String XtResolvePathname(\fIdisplay\fP, \fItype\fP, \fIfilename\fP, \fIsuffix\fP, \
\fIpath\fP, \fIsubstitutions\fP, \fInum_substitutions\fP, \fIpredicate\fP)
.br
      Display *\fIdisplay\fP;
.br
      String \fItype\fP, \fIfilename\fP, \fIsuffix\fP, \fIpath\fP;
.br
      Substitution \fIsubstitutions\fP;
.br
      Cardinal \fInum_substitutions\fP;
.br
      XtFilePredicate \fIpredicate\fP;
.FN
.IP \fIdisplay\fP 1.2i
Specifies the display to use to find the language for language substitutions.
.IP \fItype\fP
.br
.ns
.IP \fIfilename\fP
.br
.ns
.IP \fIsuffix\fP 1.2i
Specify values to substitute into the path.
.IP \fIpath\fP 1.2i
Specifies the list of file specifications, or NULL.
.IP \fIsubstitutions\fP 1.2i
Specifies a list of additional substitutions to make into the path, or NULL.
.IP \fInum_substitutions\fP 1.2i
Specifies the number of entries in \fIsubstitutions\fP.
.IP \fIpredicate\fP 1.2i
Specifies a procedure called to judge each potential file name, or NULL.
.LP
.eM
The substitutions specified by
.PN XtResolvePathname
are determined from the value of the language string retrieved by
.PN XtDisplayInitialize
for the specified display.
To set the
language for all applications specify ``*xnlLanguage: \fIlang\fP'' in the
resource database. 
.IN "xnlLanguage"
The format and content of the language string are
implementation-defined.   One suggested syntax is to compose
the language string of three parts;  a  ``language  part'',  a
``territory  part'' and a ``codeset part''.  The manner in which
this composition is accomplished is implementation-defined,
and the \*(xI make no interpretation of the parts other
than to use them in substitutions as described below.
.LP
.PN XtResolvePathname
calls
.PN XtFindFile
with the following substitutions
in addition to any passed by the caller and returns the value returned by
.PN XtFindFile :
.IP %N 5
The value of the \fIfilename\fP parameter, or the application's
class name if \fIfilename\fP is NULL.
.IP %T 5
The value of the \fItype\fP parameter.
.IP %S 5
The value of the \fIsuffix\fP parameter.
.IP %L 5
The language string associated with the specified display.
.IP %l 5
The language part of the display's language string.
.IP %t 5
The territory part of the display's language string.
.IP %c 5
The codeset part of the display's language string.
.IP %C 5
The customization string retrieved from the resource
database associated with \fIdisplay\fP.
.IP %D 5
The value of the implementation-specific default path.
.LP
If a path is passed to
.PN XtResolvePathname ,
it is passed along to
.PN XtFindFile .
If the \fIpath\fP argument is NULL, the value of the
.PN \s-1XFILESEARCHPATH\s+1
.IN "XFILESEARCHPATH" "" "@DEF@"
environment variable is passed to
.PN XtFindFile .
If
.PN \s-1XFILESEARCHPATH\s+1
is not defined, an implementation-specific default path is used
that contains at least six entries.  These entries
must contain the following substitutions:

.nf
.ta .3i 2i 2.5i
1.	%C, %N, %S, %T, %L	or	%C, %N, %S, %T, %l, %t, %c
2.	%C, %N, %S, %T, %l
3.	%C, %N, %S, %T
4.	%N, %S, %T, %L	or	%N, %S, %T, %l, %t, %c
5.	%N, %S, %T, %l
6.	%N, %S, %T
.fi

The order of these six entries within the path must be as given above.
The order and use of substitutions within a given entry
are implementation-dependent.
If the path begins
with a colon, it is preceded by %N%S.  If the path includes two
adjacent colons, \fB%N%S\fP is inserted between them.
.LP
The \fItype\fP parameter is intended to be a category of files, usually
being translated into a directory in the pathname.  Possible values
might include ``app-defaults'', ``help'', and ``bitmap''.
.LP
The \fIsuffix\fP parameter is intended to be appended to the file name.
Possible values might include ``.txt'', ``.dat'', and ``.bm''.
.LP
A suggested value for the default path on POSIX-based systems is
.IP
/usr/lib/X11/%L/%T/%N%C%S:/usr/lib/X11/%l/%T/%N%C%S:\\
.br
/usr/lib/X11/%T/%N%C%S:/usr/lib/X11/%L/%T/%N%S:\\
.br
/usr/lib/X11/%l/%T/%N%S:/usr/lib/X11/%T/%N%S

.LP
Using this example, if the user has specified a language, it is
used as a subdirectory of /usr/lib/X11 that is searched for other
files.  If the desired file is not found there, the lookup is
tried again using just the language part of the specification.  If the
file is not there, it is looked for in /usr/lib/X11.  The \fItype\fP
parameter is used as a subdirectory of the language directory or of
/usr/lib/X11, and \fIsuffix\fP is appended to the file name.
.LP
The %D substitution allows the addition of path
elements to the implementation-specific default path, typically to
allow additional directories to be searched without preventing
resources in the system directories from being found.  For example, a
user installing resource files under a directory called ``ourdir''
might set
.PN \s-1XFILESEARCHPATH\s+1
to
.IP
%D:ourdir/%T/%N%C:ourdir/%T/%N
.LP
The customization string is obtained by querying the resource database
currently associated with the display (the database returned by
.PN XrmGetDatabase )
for the resource \fIapplication_name\fP.customization, class
\fIapplication_class\fP.Customization, where \fIapplication_name\fP
and \fIapplication_class\fP are the values returned by
.PN XtGetApplicationNameAndClass .
If no value is specified in the database, the empty string is used.
.LP
It is the responsibility of the caller to free the returned string using
.PN XtFree
when it is no longer needed.

.NH 2
Hooks for External Agents
.XS
\fB\*(SN Hooks for External Agents\fP
.XE
.LP
Applications may register
functions that are called at a particular control points in the \*(xI.
These functions are intended to be used to provide notification
of an \*Q\*(tk event\*U, such as widget creation, to an external agent,
such as an interactive resource editor, drag-and-drop server, or
an aid for physically challenged users.
The control points containing such registration hooks are identified
in a \*Qhook registration\*U object.
.LP
To retrieve the hook registration widget, use
.PN XtHooksOfDisplay .
.LP
.IN "XtHooksOfDisplay" "" "@DEF@"
.sM
.FD 0
Widget XtHooksOfDisplay(\fIdisplay\fP)
.br
      Display *\fIdisplay\fP;
.FN
.IP \fIdisplay\fP 1i
Specifies the desired display.
.LP
.eM
The class of this object is a private, implementation-dependent
subclass of
.PN Object .
The hook object has no parent.  The resources of this object are 
the callback lists for hooks and the read-only resources for getting 
a list of parentless shells.  All of the callback lists are initially 
empty.  When a display is closed, the hook object associated with it 
is destroyed. 
.LP
The following procedures can be called with the hook registration object
as an argument:
.sp
.IP
.PN XtAddCallback ,
.PN XtAddCallbacks ,
.PN XtRemoveCallback ,
.PN XtRemoveCallbacks ,
.PN XtRemoveAllCallbacks ,
.PN XtCallCallbacks ,
.PN XtHasCallbacks ,
.PN XtCallCallbackList
.IP
.PN XtClass ,
.PN XtSuperclass ,
.PN XtIsSubclass ,
.PN XtCheckSubclass ,
.PN XtIsObject ,
.PN XtIsRectObj ,
.PN XtIsWidget ,
.PN XtIsComposite ,
.PN XtIsConstraint ,
.PN XtIsShell ,
.PN XtIsOverrideShell ,
.PN XtIsWMShell ,
.PN XtIsVendorShell ,
.PN XtIsTransientShell ,
.PN XtIsToplevelShell ,
.PN XtIsApplicationShell ,
.PN XtIsSessionShell
.IP
.PN XtWidgetToApplicationContext
.IP
.PN XtName ,
.PN XtParent ,
.PN XtDisplayOfObject ,
.PN XtScreenOfObject
.IP
.PN XtSetValues ,
.PN XtGetValues ,
.PN XtVaSetValues ,
.PN XtVaGetValues
.sp
.LP

.NH 3
Hook Object Resources
.XS
\fB\*(SN Hook Object Resources\fP
.XE
.LP
The resource names, classes, and representation types that are specified
in the hook object resource list are:
.KS
.TS
lw(1.5i) lw(1.5i) lw(2.5i) .
_
.sp 6p
Name	Class	Representation
.sp 6p
_
.sp 6p
XtNcreateHook	XtCCallback	XtRCallback
XtNchangeHook	XtCCallback	XtRCallback
XtNconfigureHook	XtCCallback	XtRCallback
XtNgeometryHook	XtCCallback	XtRCallback
XtNdestroyHook	XtCCallback	XtRCallback
XtNshells	XtCReadOnly	XtRWidgetList
XtNnumShells	XtCReadOnly	XtRCardinal
.sp 6p
_
.TE
.KE
.LP
Descriptions of each of these resources:
.LP
The XtNcreateHook callback list is called from:
.PN XtCreateWidget ,
.PN XtCreateManagedWidget ,
.PN XtCreatePopupShell ,
.PN XtAppCreateShell ,
and their corresponding varargs versions.
.LP
The \fIcall_data\fP parameter in a createHook callback may be 
cast to type
.PN XtCreateHookData .
.LP
.IN "XtCreateHookData" "" "@DEF@"
.sM
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	String   type;
	Widget   widget;
	ArgList  args;
	Cardinal num_args;
} XtCreateHookDataRec, *XtCreateHookData;
.De
.eM
.LP
The \fItype\fP is set to
.PN XtHcreate ,
\fIwidget\fP is the newly created widget, and \fIargs\fP and \fInum_args\fP
are the arguments passed to the create function. The callbacks are 
called before returning from the create function.
.LP
The XtNchangeHook callback list is called from:
.IP
.PN XtSetValues ,
.PN XtVaSetValues
.IP
.PN XtManageChild ,
.PN XtManageChildren ,
.PN XtUnmanageChild ,
.PN XtUnmanageChildren
.IP
.PN XtRealizeWidget ,
.PN XtUnrealizeWidget
.IP
.PN XtAddCallback ,
.PN XtRemoveCallback ,
.PN XtAddCallbacks, 
.PN XtRemoveCallbacks ,
.PN XtRemoveAllCallbacks
.IP
.PN XtAugmentTranslations ,
.PN XtOverrideTranslations ,
.PN XtUninstallTranslations
.IP
.PN XtSetKeyboardFocus ,
.PN XtSetWMColormapWindows
.IP
.PN XtSetMappedWhenManaged ,
.PN XtMapWidget ,
.PN XtUnmapWidget
.IP
.PN XtPopup ,
.PN XtPopupSpringLoaded ,
.PN XtPopdown
.LP
.sp
.LP
The \fIcall_data\fP parameter in a changeHook callback may
be cast to type
.PN XtChangeHookData .
.IN "XtChangeHookData" "" "@DFEF@"
.LP
.KS
.sM
.Ds 0
.TA .5i 2.5i
.ta .5i 2.5i
typedef struct {
	String  type;
	Widget  widget;
	XtPointer event_data;
	Cardinal num_event_data;
} XtChangeHookDataRec, *XtChangeHookData;
.De
.eM
.KE
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtSetValues
or
.PN XtVaSetValues ,
\fItype\fP is set to
.PN XtHsetValues ,
\fIwidget\fP is the new widget passed to the set_values procedure, and
\fIevent_data\fP may be cast to type 
.PN XtChangeHookSetValuesData .
.IN "XtChangeHookSetValuesData" "" "@DEF@"
.LP
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typedef struct {
	Widget   old, req;
	ArgList  args;
	Cardinal num_args;
} XtChangeHookSetValuesDataRec, *XtChangeHookSetValuesData;
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The \fIold\fP, \fIreq\fP, \fIargs\fP, and \fInum_args\fP are the
parameters passed to the set_values procedure.  The callbacks are called 
after the set_values and constraint set_values procedures have been called.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtManageChild
or
.PN XtManageChildren ,
\fItype\fP is set to
.PN XtHmanageChildren ,
\fIwidget\fP is the parent, \fIevent_data\fP may be cast to type
WidgetList and is the list of children being managed, and 
\fInum_event_data\fP is the length of the widget list.
The callbacks are called after the children have been managed.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtUnmanageChild
or
.PN XtUnmanageChildren ,
\fItype\fP is set to
.PN XtHunmanageChildren ,
\fIwidget\fP is the parent, \fIevent_data\fP may be cast to type
WidgetList and is a list of the children being unmanaged, and
\fInum_event_data\fP is the length of the widget list.
The callbacks are called after the children have been unmanaged.
.LP
The changeHook callbacks are called twice as a result of a call to
.PN XtChangeManagedSet ,
once after unmanaging and again after managing.
When the callbacks are called the first time, \fItype\fP is set to
.PN XtHunmanageSet , 
\fIwidget\fP is the parent, \fIevent_data\fP may be cast to type 
WidgetList and is a list of the children being unmanaged, and 
\fInum_event_data\fP is the length of the widget list.
When the callbacks are called the second time, the \fItype\fP is set to
.PN XtHmanageSet , 
\fIwidget\fP is the parent, \fIevent_data\fP may be cast to type 
WidgetList and is a list of the children being managed, and 
\fInum_event_data\fP is the length of the widget list.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtRealizeWidget ,
the \fItype\fP is set to
.PN XtHrealizeWidget 
and \fIwidget\fP is the widget being realized.
The callbacks are called after the widget has been realized.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtUnrealizeWidget ,
the \fItype\fP is set to
.PN XtHunrealizeWidget ,
and \fIwidget\fP is the widget being unrealized.
The callbacks are called after the widget has been unrealized.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtAddCallback ,
\fItype\fP is set to
.PN XtHaddCallback ,
\fIwidget\fP is the widget to which the callback is being added, and
\fIevent_data\fP may be cast to type String and is the name of the 
callback being added.
The callbacks are called after the callback has been added to the widget.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtAddCallbacks ,
the \fItype\fP is set to
.PN XtHaddCallbacks ,
\fIwidget\fP is the widget to which the callbacks are being added, and
\fIevent_data\fP may be cast to type String and is the name of the 
callbacks being added.
The callbacks are called after the callbacks have been added to the widget.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtRemoveCallback ,
the \fItype\fP is set to
.PN XtHremoveCallback ,
\fIwidget\fP is the widget from which the callback is being removed, and
\fIevent_data\fP may be cast to type String and is the name of
the callback being removed.  The callbacks are called after the callback 
has been removed from the widget.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtRemoveCallbacks ,
the \fItype\fP is set to
.PN XtHremoveCallbacks ,
\fIwidget\fP is the widget from which the callbacks are being removed, and
\fIevent_data\fP may be cast to type String and is the name of the 
callbacks being removed.  The callbacks are called after the callbacks 
have been removed from the widget.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtRemoveAllCallbacks ,
the \fItype\fP is set to
.PN XtHremoveAllCallbacks
and \fIwidget\fP is the widget from which the callbacks are being removed.
The callbacks are called after the callbacks have been removed from the
widget.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtAugmentTranslations ,
the \fItype\fP is set to
.PN XtHaugmentTranslations
and \fIwidget\fP is the widget whose translations are being modified.
The callbacks are called after the widget's translations have been 
modified.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtOverrideTranslations ,
the \fItype\fP is set to
.PN XtHoverrideTranslations
and \fIwidget\fP is the widget whose translations are being modified.
The callbacks are called after the widget's translations have been 
modified.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtUninstallTranslations ,
The \fItype\fP is
.PN XtHuninstallTranslations
and \fIwidget\fP is the widget whose translations are being uninstalled.
The callbacks are called after the widget's translations have been 
uninstalled.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtSetKeyboardFocus ,
the \fItype\fP is set to
.PN XtHsetKeyboardFocus
and \fIevent_data\fP may be cast to type Widget and is the value of 
the descendant argument passed to \fBXtSetKeyboardFocus\fP. The 
callbacks are called before returning from \fBXtSetKeyboardFocus\fP.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtSetWMColormapWindows ,
\fItype\fP is set to
.PN XtHsetWMColormapWindows ,
\fIevent_data\fP may be cast to type WidgetList and is the value of 
the list argument passed to \fBXtSetWMColormapWindows\fP, and 
\fInum_event_data\fP is the length of the list. The callbacks are 
called before returning from \fBXtSetWMColormapWindows\fP.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtSetMappedWhenManaged ,
the \fItype\fP is set to
.PN XtHsetMappedWhenManaged
and \fIevent_data\fP may be cast to type Boolean and is the value of 
the mapped_when_managed argument passed to \fBXtSetMappedWhenManaged\fP. 
The callbacks are called after setting the widget's mapped_when_managed 
field and before realizing or unrealizing the widget.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtMapWidget ,
the \fItype \fP is set to
.PN XtHmapWidget
and \fIwidget\fP is the widget being mapped.
The callbacks are called after mapping the widget.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtUnmapWidget ,
the \fItype \fP is set to
.PN XtHunmapWidget
and \fIwidget\fP is the widget being unmapped.
The callbacks are called after unmapping the widget.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtPopup ,
the \fItype\fP is set to
.PN XtHpopup ,
\fIwidget\fP is the widget being popped up, and \fIevent_data\fP may 
be cast to type XtGrabKind and is the value of the grab_kind argument 
passed to \fBXtPopup\fP.
The callbacks are called before returning from \fBXtPopup\fP.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtPopupSpringLoaded ,
the \fItype\fP is set to
.PN XtHpopupSpringLoaded
and \fIwidget\fP is the widget being popped up.
The callbacks are called 
before returning from \fBXtPopupSpringLoaded\fP.
.LP
When the changeHook callbacks are called as a result of a call to
.PN XtPopdown ,
the \fItype\fP is set to
.PN XtHpopdown
and \fIwidget\fP is the widget being popped down.
The callbacks are called 
before returning from \fBXtPopdown\fP.
.LP
A widget set that exports interfaces that change application state
without employing the \*(xI library should invoke the change hook
itself.  This is done by:
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        XtCallCallbacks(XtHooksOfDisplay(dpy), XtNchangeHook, call_data);
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The XtNconfigureHook callback list is called any time the \*(xI
move, resize, or configure a widget and when
.PN XtResizeWindow
is called.
.LP
The \fIcall_data\fP parameter may be cast to type
.PN XtConfigureHookData.
.LP
.IN "XtConfigureHookData" "" "@DEF@"
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typedef struct {
	String type;
	Widget widget;
	XtGeometryMask changeMask;
	XWindowChanges changes;	
} XtConfigureHookDataRec, *XtConfigureHookData;
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When the configureHook callbacks are called, the \fItype\fP is
.PN XtHconfigure ,
\fIwidget\fP is the widget being configured, and \fIchangeMask\fP and 
\fIchanges\fP reflect the changes made to the widget. The callbacks 
are called after changes have been made to the widget.
.LP
The XtNgeometryHook callback list is called from 
.PN XtMakeGeometryRequest
and
.PN XtMakeResizeRequest
once before and once after geometry negotiation occurs.
.LP
The \fIcall_data\fP parameter may be cast to type
.PN XtGeometryHookData .
.LP
.IN "XtGeometryHookData" "" "@DFEF@"
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typedef struct {
	String type;
	Widget widget;
	XtWidgetGeometry* request;
	XtWidgetGeometry* reply;
	XtGeometryResult result;
} XtGeometryHookDataRec, *XtGeometryHookData;
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When the geometryHook callbacks are called prior to geometry negotiation, 
the \fItype\fP is
.PN XtHpreGeometry ,
\fIwidget\fP is the widget for which the request is being made, and
\fIrequest\fP is the requested geometry.
When the geometryHook callbacks 
are called after geometry negotiation, the \fItype\fP is
.PN XtHpostGeometry ,
\fIwidget\fP is the widget for which the request was made, \fIrequest\fP
is the requested geometry, \fIreply\fP is the resulting geometry granted, 
and \fIresult\fP is the value returned from the geometry negotiation.
.LP
The XtNdestroyHook callback list is called when a widget is destroyed.
The \fIcall_data parameter\fP may be cast to type
.PN XtDestroyHookData .
.LP
.IN "XtDestroyHookData" "" "@DFEF@"
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typedef struct {
	String type;
	Widget widget;
} XtDestroyHookDataRec, *XtDestroyHookData;
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When the destroyHook callbacks are called as a result of a call to
.PN XtDestroyWidget ,
the \fItype\fP is
.PN XtHdestroy
and \fIwidget\fP is the widget being destroyed. The callbacks are
called upon completion of phase one destroy for a widget.
.LP
The XtNshells and XtnumShells are read-only resources that report a
list of all parentless shell widgets associated with a display.
.LP
Clients who use these hooks must exercise caution in calling \*(xI
functions in order to avoid recursion.

.NH 3
Querying Open Displays
.XS
\fB\*(SN Querying Open Displays\fP
.XE
.LP
To retrieve a list of the Displays associated with an application context,
use
.PN XtGetDisplays .
.LP
.IN "XtGetDisplays" "" "@DEF@"
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void XtGetDisplays(\fIapp_context\fP, \fIdpy_return\fP, \fInum_dpy_return\fP)
.br
      XtAppContext \fIapp_context\fP;
.br
      Display ***\fIdpy_return\fP;
.br
      Cardinal *\fInum_dpy_return\fP;
.FN
.IP \fIapp_context\fP 1.5i
Specifies the application context.
.IP \fIdpy_return\fP 1.5i
Returns a list of open Display connections in the specified application
context.
.IP \fInum_dpy_return\fP 1.5i
Returns the count of open Display connections in \fIdpy_return\fP.
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\fBXtGetDisplays\fP may be used by an external agent to query the
list of open displays that belong to an application context. To free 
the list of displays, use
.PN XtFree .
.bp
