# Utility Functions

The Intrinsics provide a number of utility functions that you can use to

- Determine the number of elements in an array.

- Translate strings to widget instances.

- Manage memory usage.

- Share graphics contexts.

- Manipulate selections.

- Merge exposure events into a region.

- Translate widget coordinates.

- Locate a widget given a window id.

- Handle errors.

- Set the WM_COLORMAP_WINDOWS property.

- Locate files by name with string substitutions.

- Register callback functions for external agents.

- Locate all the displays of an application context.

## Determining the Number of Elements in an Array

To determine the number of elements in a fixed-size array, use .

    Cardinal XtNumber
      ArrayType array

array

  Specifies a fixed-size array of arbitrary type.

The macro returns the number of elements allocated to the array.

## Translating Strings to Widget Instances

To translate a widget name to a widget instance, use .

    Widget XtNameToWidget
       Widget reference
       const char * names

reference

  Specifies the widget from which the search is to start. Must be of class Core or any subclass thereof.

names

  Specifies the partially qualified name of the desired widget.

The function searches for a descendant of the reference widget whose name matches the specified names. The names parameter specifies a simple object name or a series of simple object name components separated by periods or asterisks. 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 :

- 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.

- Return the first object in the enumeration that matches the specified name, where each component of names matches exactly the corresponding component of the qualified object name and asterisk matches any series of components, including none.

- If no match is found, return NULL.

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 Intrinsics do not require that all children of a widget have unique names, 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.

## Managing Memory Usage

The Intrinsics 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 `malloc`, `calloc`, `realloc`, and `free` with the following added functionality:

- , , and give an error if there is not enough memory.

- simply returns if passed a NULL pointer.

- simply allocates new storage if passed a NULL pointer.

See the standard C library documentation on `malloc`, `calloc`, `realloc`, and `free` for more information.

To allocate storage, use .

    char * XtMalloc
       Cardinal size

size

  Specifies the number of bytes desired.

The function returns a pointer to a block of storage of at least the specified size bytes. If there is insufficient memory to allocate the new block, calls .

To allocate and initialize an array, use .

    char * XtCalloc
       Cardinal num
       Cardinal size

num

  Specifies the number of array elements to allocate.

size

  Specifies the size of each array element in bytes.

The 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, calls . returns the address of the allocated storage.

To change the size of an allocated block of storage, use .

    char *XtRealloc
       char *ptr
       Cardinal num

ptr

  Specifies a pointer to the old storage allocated with , , or , or NULL.

num

  Specifies number of bytes desired in new storage.

The 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, calls . If ptr is NULL, simply calls . then returns the address of the new block.

To free an allocated block of storage, use .

    void XtFree
       char *ptr

ptr

  Specifies a pointer to a block of storage allocated with , , or , or NULL.

The function returns storage, allowing it to be reused. If ptr is NULL, returns immediately.

To allocate storage for a new instance of a type, use .

    type XtNew
          type t

type

  Specifies a previously declared type.

returns a pointer to the allocated storage. If there is insufficient memory to allocate the new block, calls . is a convenience macro that calls with the following arguments specified:

    ((type *) XtMalloc((unsigned) sizeof(type)))

The storage allocated by should be freed using .

To copy an instance of a string, use .

    String XtNewString
       String string

string

  Specifies a previously declared string.

returns a pointer to the allocated storage. If there is insufficient memory to allocate the new block, calls . is a convenience macro that calls with the following arguments specified:

    (strcpy(XtMalloc((unsigned)strlen(str) + 1), str))

The storage allocated by should be freed using .

## Sharing Graphics Contexts

The Intrinsics 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.

To obtain a shareable GC with modifiable fields, use .

    GC XtAllocateGC
       Widget object
       Cardinal depth
       XtGCMask value_mask
       XGCValues *values
       XtGCMask dynamic_mask
       XtGCMask unused_mask

object

  Specifies an object, giving the screen for which the returned GC is valid. Must be of class Object or any subclass thereof.

depth

  Specifies the depth for which the returned GC is valid, or 0.

value_mask

  Specifies fields of the GC that are initialized from values.

values

  Specifies the values for the initialized fields.

dynamic_mask

  Specifies fields of the GC that will be modified by the caller.

unused_mask

  Specifies fields of the GC that will not be needed by the caller.

The function returns a shareable GC that may be modified by the client. The screen field of the specified widget or of the nearest widget ancestor of the specified object and the specified depth argument supply the root and drawable depths for which the GC is to be valid. If depth is zero, the depth is taken from the depth field of the specified widget or of the nearest widget ancestor of the specified object.

The value_mask argument specifies fields of the GC that are initialized with the respective member of the values structure. The dynamic_mask 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 unused_mask 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 unused_mask. The caller may assume that at all times all fields not specified in either dynamic_mask or unused_mask have their default value if not specified in value_mask or the value specified by values. If a field is specified in both value_mask and dynamic_mask, the effect is as if it were specified only in dynamic_mask and then immediately set to the value in values. If a field is set in unused_mask and also in either value_mask or dynamic_mask, the specification in unused_mask is ignored.

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. may modify and return an existing GC if it was allocated with a nonzero unused_mask.

To obtain a shareable GC with no modifiable fields, use .

    GC XtGetGC
       Widget object
       XtGCMask value_mask
       XGCValues *values

object

  Specifies an object, giving the screen and depth for which the returned GC is valid. Must be of class Object or any subclass thereof.

value_mask

  Specifies which fields of the values structure are specified.

values

  Specifies the actual values for this GC.

The function returns a shareable, read-only GC. The parameters to this function are the same as those for `XCreateGC` except that an Object is passed instead of a Display. is equivalent to with depth, dynamic_mask, and unused_mask all zero.

shares only GCs in which all values in the GC returned by `XCreateGC` are the same. In particular, it does not use the value_mask provided to determine which fields of the GC a widget considers relevant. The value_mask is used only to tell the server which fields should be filled in from values and which it should fill in with default values.

To deallocate a shared GC when it is no longer needed, use .

    void XtReleaseGC
       Widget object
       GC gc

object

  Specifies any object on the Display for which the GC was created. Must be of class Object or any subclass thereof.

gc

  Specifies the shared GC obtained with either or .

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.

## Managing Selections

Arbitrary widgets in multiple applications can communicate with each other by means of the Intrinsics global selection mechanism, which conforms to the specifications in the Inter-Client Communication Conventions Manual. The Intrinsics supply functions for providing and receiving selection data in one logical piece (atomic transfers) or in smaller logical segments (incremental transfers).

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 Intrinsics 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 Intrinsics is not required to match the underlying transport protocol between the application and the X server; the Intrinsics 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.

### Setting and Getting the Selection Timeout Value

To set the Intrinsics selection timeout, use .

    void XtAppSetSelectionTimeout
       XtAppContext app_context
       unsigned long timeout

app_context

  Specifies the application context.

timeout

  Specifies the selection timeout in milliseconds.

To get the current selection timeout value, use .

    unsigned long XtAppGetSelectionTimeout
       XtAppContext app_context

app_context

  Specifies the application context.

The 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 application resource as retrieved by . If selectionTimeout is not specified, the default is five seconds.

### Using Atomic Transfers

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.

#### Atomic Transfer Procedures

The following procedures are used by the selection owner when providing selection data in a single unit.

The procedure pointer specified by the owner to supply the selection data to the Intrinsics is of type .

    typedef Boolean (*XtConvertSelectionProc)
       Widget w
       Atom *selection
       Atom *target
       Atom *type_return
       XtPointer *value_return
       unsigned long *length_return
       int *format_return

w

  Specifies the widget that currently owns this selection.

selection

  Specifies the atom naming the selection requested (for example, `XA_PRIMARY` or `XA_SECONDARY ).`

target

  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).

type_return

  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 `XA_STRING`.

value_return

  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 for the selection, this storage is owned by the selection owner; otherwise, it is owned by the Intrinsics selection mechanism, which frees it by calling when it is done with it.

length_return

  Specifies a pointer into which the number of elements in value_return, each of size indicated by format_return, is to be stored.

format_return

  Specifies a pointer into which the size in bits of the data elements of the selection value is to be stored.

This procedure is called by the Intrinsics selection mechanism to get the value of a selection as a given type from the current selection owner. It returns `True` if the owner successfully converted the selection to the target type or `False` otherwise. If the procedure returns `False`, the values of the return arguments are undefined. Each should respond to target value `TARGETS` by returning a value containing the list of the targets into which it is prepared to convert the selection. The value returned in format_return must be one of 8, 16, or 32 to allow the server to byte-swap the data if necessary.

This procedure does not need to worry about responding to the MULTIPLE or the TIMESTAMP target values (see in the Inter-Client Communication Conventions Manual). 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 Intrinsics using the time specified in the call to or .

To retrieve the `SelectionRequest` event that triggered the procedure, use .

    XSelectionRequestEvent *XtGetSelectionRequest
       Widget w
       Atom selection
       XtRequestId request_id

w

  Specifies the widget that currently owns this selection. Must be of class Core or any subclass thereof.

selection

  Specifies the selection being processed.

request_id

  Specifies the requestor id in the case of incremental selections, or NULL in the case of atomic transfers.

may be called only from within an procedure and returns a pointer to the `SelectionRequest` event that caused the conversion procedure to be invoked. Request_id specifies a unique id for the individual request in the case that multiple incremental transfers are outstanding. For atomic transfers, request_id must be specified as NULL. If no `SelectionRequest` event is being processed for the specified widget, selection, and request_id, returns NULL.

The procedure pointer specified by the owner when it desires notification upon losing ownership is of type .

    typedef void (*XtLoseSelectionProc)
       Widget w
       Atom *selection

w

  Specifies the widget that has lost selection ownership.

selection

  Specifies the atom naming the selection.

This procedure is called by the Intrinsics 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.

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 .

    typedef void (*XtSelectionDoneProc)
       Widget w
       Atom *selection
       Atom *target

w

  Specifies the widget that owns the converted selection.

selection

  Specifies the atom naming the selection that was converted.

target

  Specifies the target type to which the conversion was done.

This procedure is called by the Intrinsics selection mechanism to inform the selection owner that a selection requestor has successfully retrieved a selection value. If the selection owner has registered an , 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 , it also owns the storage containing the converted selection value.

#### Getting the Selection Value

The procedure pointer specified by the requestor to receive the selection data from the Intrinsics is of type .

    typedef void (*XtSelectionCallbackProc)
       Widget w
       XtPointer client_data
       Atom *selection
       Atom *type
       XtPointer value
       unsigned long *length
       int *format

w

  Specifies the widget that requested the selection value.

client_data

  Specifies a value passed in by the widget when it requested the selection.

selection

  Specifies the name of the selection that was requested.

type

  Specifies the representation type of the selection value (for example, `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 `XT_CONVERT_FAIL` is used to indicate that the selection conversion failed because the selection owner did not respond within the Intrinsics selection timeout interval.

value

  Specifies a pointer to the selection value. The requesting client owns this storage and is responsible for freeing it by calling when it is done with it.

length

  Specifies the number of elements in value.

format

  Specifies the size in bits of the data in each element of value.

This procedure is called by the Intrinsics selection mechanism to deliver the requested selection to the requestor.

If the `SelectionNotify` event returns a property of `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.

To obtain the selection value in a single logical unit, use or .

    void XtGetSelectionValue
       Widget w
       Atom selection
       Atom target
       XtSelectionCallbackProc callback
       XtPointer client_data
       Time time

w

  Specifies the widget making the request. Must be of class Core or any subclass thereof.

selection

  Specifies the particular selection desired; for example, `XA_PRIMARY`.

target

  Specifies the type of information needed about the selection.

callback

  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.

client_data

  Specifies additional data to be passed to the specified procedure when it is called.

time

  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 `CurrentTime` is not acceptable.

The function requests the value of the selection converted to the target type. The specified callback is called at some time after is called, when the selection value is received from the X server. It may be called before or after returns. For more information about selection, target, and time, see Section 2.6 in the Inter-Client Communication Conventions Manual.

    void XtGetSelectionValues
       Widget w
       Atom selection
       Atom *targets
       int count
       XtSelectionCallbackProc callback
       XtPointer *client_data
       Time time

w

  Specifies the widget making the request. Must be of class Core or any subclass thereof.

selection

  Specifies the particular selection desired (that is, primary or secondary).

targets

  Specifies the types of information needed about the selection.

count

  Specifies the length of the targets and client_data lists.

callback

  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.

client_data

  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.

time

  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 `CurrentTime` is not acceptable.

The function is similar to multiple calls to 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 selection, target, and time, see section 2.6 in the Inter-Client Communication Conventions Manual.

#### Setting the Selection Owner

To set the selection owner and indicate that the selection value will be provided in one piece, use .

    Boolean XtOwnSelection
       Widget w
       Atom selection
       Time time
       XtConvertSelectionProc convert_proc
       XtLoseSelectionProc lose_selection
       XtSelectionDoneProc done_proc

w

  Specifies the widget that wishes to become the owner. Must be of class Core or any subclass thereof.

selection

  Specifies the name of the selection (for example, `XA_PRIMARY ).`

time

  Specifies the timestamp that indicates when the ownership request was initiated. This should be the timestamp of the event that triggered ownership; the value `CurrentTime` is not acceptable.

convert_proc

  Specifies the procedure to be called whenever a client requests the current value of the selection.

lose_selection

  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.

done_proc

  Specifies the procedure called after the requestor has received the selection value, or NULL if the owner is not interested in being called back.

The function informs the Intrinsics selection mechanism that a widget wishes to own a selection. It returns `True` if the widget successfully becomes the owner and `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.

If a done_proc is specified, the client owns the storage allocated for passing the value to the Intrinsics. If done_proc is NULL, the convert_proc must allocate storage using , , or , and the value specified is freed by the Intrinsics when the transfer is complete.

Usually, a selection owner maintains ownership indefinitely until some other widget requests ownership, at which time the Intrinsics 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 Intrinsics by using that it no longer is to be the selection owner.

    void XtDisownSelection
       Widget w
       Atom selection
       Time time

w

  Specifies the widget that wishes to relinquish ownership.

selection

  Specifies the atom naming the selection being given up.

time

  Specifies the timestamp that indicates when the request to relinquish selection ownership was initiated.

The function informs the Intrinsics 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, does nothing.

After a widget has called , 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 finishes after the call to .

### Using Incremental Transfers

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 request_id argument, which is an identifier that is guaranteed to be unique among all incremental requests that are active concurrently.

For example, consider the following:

- Upon receiving a request for the selection value, the owner sends the first segment.

- 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.

- 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.

#### Incremental Transfer Procedures

The following procedures are used by selection owners who wish to provide the selection data in multiple segments.

The procedure pointer specified by the incremental owner to supply the selection data to the Intrinsics is of type .

    typedef XtPointer XtRequestId;

    typedef Boolean (*XtConvertSelectionIncrProc)
       Widget w
       Atom *selection
       Atom *target
       Atom *type_return
       XtPointer *value_return
       unsigned long *length_return
       int *format_return
       unsigned long *max_length
       XtPointer client_data
       XtRequestId *request_id

w

  Specifies the widget that currently owns this selection.

selection

  Specifies the atom that names the selection requested.

target

  Specifies the type of information required about the selection.

type_return

  Specifies a pointer to an atom into which the property type of the converted value of the selection is to be stored.

value_return

  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.

length_return

  Specifies a pointer into which the number of elements in value_return, each of size indicated by format_return, is to be stored.

format_return

  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.

max_length

  Specifies the maximum number of bytes which may be transferred at any one time.

client_data

  Specifies the value passed in by the widget when it took ownership of the selection.

request_id

  Specifies an opaque identification for a specific request.

This procedure is called repeatedly by the Intrinsics selection mechanism to get the next incremental chunk of data from a selection owner who has called . It must return `True` if the procedure has succeeded in converting the selection data or `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 Intrinsics; that is, a fixed transfer area may be allocated and returned in value_return for each segment to be transferred. This procedure should store a non-NULL value in value_return and zero in length_return to indicate that the entire selection has been delivered. After returning this final segment, the request id may be reused by the Intrinsics to begin a new transfer.

To retrieve the `SelectionRequest` event that triggered the selection conversion procedure, use , described in Section 11.5.2.1.

The procedure pointer specified by the incremental selection owner when it desires notification upon no longer having ownership is of type .

    typedef void (*XtLoseSelectionIncrProc)
       Widget w
       Atom *selection
       XtPointer client_data

w

  Specifies the widget that has lost the selection ownership.

selection

  Specifies the atom that names the selection.

client_data

  Specifies the value passed in by the widget when it took ownership of the selection.

This procedure, which is optional, is called by the Intrinsics to inform the selection owner that it no longer owns the selection.

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 .

    typedef void (*XtSelectionDoneIncrProc)
       Widget w
       Atom *selection
       Atom *target
       XtRequestId *request_id
       XtPointer client_data

w

  Specifies the widget that owns the selection.

selection

  Specifies the atom that names the selection being transferred.

target

  Specifies the target type to which the conversion was done.

request_id

  Specifies an opaque identification for a specific request.

client_data

  Specified the value passed in by the widget when it took ownership of the selection.

This procedure, which is optional, is called by the Intrinsics 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 Intrinsics will free only the final value returned by the selection owner using .

The procedure pointer specified by the incremental selection owner to notify it if a transfer should be terminated prematurely is of type .

    typedef void (*XtCancelConvertSelectionProc)
       Widget w
       Atom *selection
       Atom *target
       XtRequestId *request_id
       XtPointer client_data

w

  Specifies the widget that owns the selection.

selection

  Specifies the atom that names the selection being transferred.

target

  Specifies the target type to which the conversion was done.

request_id

  Specifies an opaque identification for a specific request.

client_data

  Specifies the value passed in by the widget when it took ownership of the selection.

This procedure is called by the Intrinsics 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.

#### Getting the Selection Value Incrementally

To obtain the value of the selection using incremental transfers, use or .

    void XtGetSelectionValueIncremental
       Widget w
       Atom selection
       Atom target
       XtSelectionCallbackProc selection_callback
       XtPointer client_data
       Time time

w

  Specifies the widget making the request. Must be of class Core or any subclass thereof.

selection

  Specifies the particular selection desired.

target

  Specifies the type of information needed about the selection.

selection_callback

  Specifies the callback procedure to be called to receive each data segment.

client_data

  Specifies client-specific data to be passed to the specified callback procedure when it is invoked.

time

  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 `CurrentTime` is not acceptable.

The function is similar to 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 selection_callback 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 `XT_CONVERT_FAIL` so that the requestor can dispose of the partial selection value it has collected up until that point. Upon receiving `XT_CONVERT_FAIL`, the requesting client must determine for itself whether or not a partially completed data transfer is meaningful. For more information about selection, target, and time, see Use of Selection Atoms in the Inter-Client Communication Conventions Manual.

    void XtGetSelectionValuesIncremental
       Widget w
       Atom selection
       Atom *targets
       int count
       XtSelectionCallbackProc selection_callback
       XtPointer *client_data
       Time time

w

  Specifies the widget making the request. Must be of class Core or any subclass thereof.

selection

  Specifies the particular selection desired.

targets

  Specifies the types of information needed about the selection.

count

  Specifies the length of the targets and client_data lists.

selection_callback

  Specifies the callback procedure to be called to receive each selection value.

client_data

  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.

time

  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 `CurrentTime` is not acceptable.

The function is similar to except that it takes a list of targets and client data. is equivalent to calling successively for each target/client_data pair except that 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 repeatedly. For more information about selection, target, and time, see Section 2.6 in the Inter-Client Communication Conventions Manual.

#### Setting the Selection Owner for Incremental Transfers

To set the selection owner when using incremental transfers, use .

    Boolean XtOwnSelectionIncremental
       Widget w
       Atom selection
       Time time
       XtConvertSelectionIncrProc convert_callback
       XtLoseSelectionIncrProc lose_callback
       XtSelectionDoneIncrProc done_callback
       XtCancelConvertSelectionProc cancel_callback
       XtPointer client_data

w

  Specifies the widget that wishes to become the owner. Must be of class Core or any subclass thereof.

selection

  Specifies the atom that names the selection.

time

  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 `CurrentTime` is not acceptable.

convert_callback

  Specifies the procedure to be called whenever the current value of the selection is requested.

lose_callback

  Specifies the procedure to be called whenever the widget has lost selection ownership, or NULL if the owner is not interested in being notified.

done_callback

  Specifies the procedure called after the requestor has received the entire selection, or NULL if the owner is not interested in being notified.

cancel_callback

  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.

client_data

  Specifies the argument to be passed to each of the callback procedures when they are called.

The procedure informs the Intrinsics incremental selection mechanism that the specified widget wishes to own the selection. It returns `True` if the specified widget successfully becomes the selection owner or `False` otherwise. For more information about selection, target, and time, see Section 2.6 in the Inter-Client Communication Conventions Manual.

If a done_callback procedure is specified, the client owns the storage allocated for passing the value to the Intrinsics. If done_callback is NULL, the convert_callback procedure must allocate storage using , , or , and the final value specified is freed by the Intrinsics 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.

The lose_callback procedure does not indicate completion of any in-progress transfers; it is invoked at the time a `SelectionClear` event is dispatched regardless of any active transfers, which are still expected to continue.

A widget that becomes the selection owner using may use to relinquish selection ownership.

### Setting and Retrieving Selection Target Parameters

To specify target parameters for a selection request with a single target, use .

    void XtSetSelectionParameters
       Widget requestor
       Atom selection
       Atom type
       XtPointer value
       unsigned long length
       int format

requestor

  Specifies the widget making the request. Must be of class Core or any subclass thereof.

selection

  Specifies the atom that names the selection.

type

  Specifies the type of the property in which the parameters are passed.

value

  Specifies a pointer to the parameters.

length

  Specifies the number of elements containing data in value, each element of a size indicated by format.

format

  Specifies the size in bits of the data in the elements of value.

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 or to specifying the same requestor widget and selection atom will generate a `ConvertSelection` request referring to the property containing the parameters. If 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.

The possible values of format are 8, 16, or 32. If the format is 8, the elements of value are assumed to be sizeof(char); if 16, sizeof(short); if 32, sizeof(long).

To generate a MULTIPLE target request with parameters for any of the multiple targets of the selection request, precede individual calls to and with corresponding individual calls to , and enclose these all within and `XtSendSelectionRequest.` and cannot be used to make selection requests with parameterized targets.

To retrieve any target parameters needed to perform a selection conversion, the selection owner calls .

    void XtGetSelectionParameters
       Widget owner
       Atom selection
       XtRequestId request_id
       Atom *type_return
       XtPointer *value_return
       unsigned long *length_return
       int *format_return

owner

  Specifies the widget that owns the specified selection.

selection

  Specifies the selection being processed.

request_id

  Specifies the requestor id in the case of incremental selections, or NULL in the case of atomic transfers.

type_return

  Specifies a pointer to an atom in which the property type of the parameters is stored.

value_return

  Specifies a pointer into which a pointer to the parameters is to be stored. A NULL is stored if no parameters accompany the request.

length_return

  Specifies a pointer into which the number of data elements in value_return of size indicated by format_return are stored.

format_return

  Specifies a pointer into which the size in bits of the parameter data in the elements of value is stored.

may be called only from within an or from within the first call to an with a new request_id.

It is the responsibility of the caller to free the returned parameters using when the parameters are no longer needed.

### Generating MULTIPLE Requests

To have the Intrinsics bundle multiple calls to make selection requests into a single request using a MULTIPLE target, use and .

    void XtCreateSelectionRequest
       Widget requestor
       Atom selection

requestor

  Specifies the widget making the request. Must be of class Core or any subclass thereof.

selection

  Specifies the particular selection desired.

When is called, subsequent calls to , , , and , with the requestor and selection as specified to , are bundled into a single selection request with multiple targets. The request is made by calling .

    void XtSendSelectionRequest
       Widget requestor
       Atom selection
       Time time

requestor

  Specifies the widget making the request. Must be of class Core or any subclass thereof.

selection

  Specifies the particular selection desired.

time

  Specifies the timestamp that indicates when the selection request was initiated. The value `CurrentTime` is not acceptable.

When is called with a value of requestor and selection matching a previous call to , 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 , , , and are invoked.

Multi-threaded applications should lock the application context before calling and release the lock after calling 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.

To relinquish the composition of a MULTIPLE request without sending it, use .

    void XtCancelSelectionRequest
       Widget requestor
       Atom selection

requestor

  Specifies the widget making the request. Must be of class Core or any subclass thereof.

selection

  Specifies the particular selection desired.

When is called, any requests queued since the last call to for the same widget and selection are discarded and any resources reserved are released. A subsequent call to will not result in any request being made. Subsequent calls to , , , or will not be deferred.

### Auxiliary Selection Properties

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 Intrinsics provides two interfaces for acquiring temporary property names.

To acquire a temporary property name atom for use in a selection request, the client may call .

    Atom XtReservePropertyAtom
       Widget w

w

  Specifies the widget making a selection request.

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.

To return a temporary property name atom for reuse and to delete the property named by that atom, use .

    void XtReleasePropertyAtom
       Widget w
       Atom atom

w

  Specifies the widget used to reserve the property name atom.

atom

  Specifies the property name atom returned by that is to be released for reuse.

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 atom does not specify a value returned by for the specified widget, the results are undefined.

### Retrieving the Most Recent Timestamp

To retrieve the timestamp from the most recent call to that contained a timestamp, use .

    Time XtLastTimestampProcessed
       Display *display

display

  Specifies an open display connection.

If no `KeyPress`, `KeyRelease`, `ButtonPress`, `ButtonRelease`, `MotionNotify`, `EnterNotify`, `LeaveNotify`, `PropertyNotify`, or `SelectionClear` event has yet been passed to for the specified display, returns zero.

### Retrieving the Most Recent Event

To retrieve the event from the most recent call to for a specific display, use .

    XEvent *XtLastEventProcessed
       Display *display

display

  Specifies the display connection from which to retrieve the event.

Returns the last event passed to for the specified display. Returns NULL if there is no such event. The client must not modify the contents of the returned event.

## Merging Exposure Events into a Region

The Intrinsics provide an utility function that merges `Expose` and `GraphicsExpose` events into a region for clients to process at once rather than processing individual rectangles. For further information about regions, see Manipulating Regions in Xlib — C Language X Interface.

To merge `Expose` and `GraphicsExpose` events into a region, use .

    void XtAddExposureToRegion
       XEvent *event
       Region region

event

  Specifies a pointer to the `Expose` or `GraphicsExpose` event.

region

  Specifies the region object (as defined in `<X11/Xutil.h>`).

The function computes the union of the rectangle defined by the exposure event and the specified region. Then it stores the results back in region. If the event argument is not an `Expose` or `GraphicsExpose` event, returns without an error and without modifying region.

This function is used by the exposure compression mechanism; see

## Translating Widget Coordinates

To translate an x-y coordinate pair from widget coordinates to root window absolute coordinates, use .

    void XtTranslateCoords
       Widget w
       Position x
       Position y
       Position *rootx_return
       Position *rooty_return

w

  Specifies the widget. Must be of class RectObj or any subclass thereof.

x

y

  Specify the widget-relative x and y coordinates.

rootx_return

rooty_return

  Return the root-relative x and y coordinates.

While is similar to the Xlib `XTranslateCoordinates` function, it does not generate a server request because all the required information already is in the widget's data structures.

## Translating a Window to a Widget

To translate a given window and display pointer into a widget instance, use .

    Widget XtWindowToWidget
       Display *display
       Window window

display

  Specifies the display on which the window is defined.

window

  Specifies the drawable for which you want the widget.

If there is a realized widget whose window is the specified drawable on the specified display, returns that widget. If not and if the drawable has been associated with a widget through , returns the widget associated with the drawable. In other cases it returns NULL.

## Handling Errors

The Intrinsics 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.

Two levels of interface are provided:

- A high-level interface that takes an error name and class and retrieves the error message text from an error resource database.

- A low-level interface that takes a simple string to display.

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.

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.

To obtain the error database (for example, to merge with an application- or widget-specific database), use .

     XrmDatabase *XtAppGetErrorDatabase
       XtAppContext app_context

app_context

  Specifies the application context.

The function returns the address of the error database. The Intrinsics do a lazy binding of the error database and do not merge in the database file until the first call to .

For a complete listing of all errors and warnings that can be generated by the Intrinsics, see

The high-level error and warning handler procedure pointers are of type .

    typedef void (*XtErrorMsgHandler)
       String name
       String type
       String class
       String defaultp
       String *params
       Cardinal *num_params

name

  Specifies the name to be concatenated with the specified type to form the resource name of the error message.

type

  Specifies the type to be concatenated with the name to form the resource name of the error message.

class

  Specifies the resource class of the error message.

defaultp

  Specifies the default message to use if no error database entry is found.

params

  Specifies a pointer to a list of parameters to be substituted in the message.

num_params

  Specifies the number of entries in params.

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 `printf` notation is used to substitute the parameters into the message.

An error message handler can obtain the error database text for an error or a warning by calling .

    void XtAppGetErrorDatabaseText
       XtAppContext app_context
       const char * name
       const char * type
       const char * class
       const char * default
       char * buffer_return
       int nbytes
       XrmDatabase database

app_context

  Specifies the application context.

name
type

  Specify the name and type concatenated to form the resource name of the error message.

class

  Specifies the resource class of the error message.

default

  Specifies the default message to use if an error database entry is not found.

buffer_return

  Specifies the buffer into which the error message is to be returned.

nbytes

  Specifies the size of the buffer in bytes.

database

  Specifies the name of the alternative database to be used, or NULL if the application context's error database is to be used.

The 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 name and type are concatenated with a single “.” between them and the class is concatenated with itself with a single “.” if it does not already contain a “.”.

To return the application name and class as passed to for a particular Display, use .

    void XtGetApplicationNameAndClass
        Display* display
        String* name_return
        String* class_return

display

  Specifies an open display connection that has been initialized with .

name_return

  Returns the application name.

class_return

  Returns the application class.

returns the application name and class passed to 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 Intrinsics and must not be modified or freed by the caller.

To register a procedure to be called on fatal error conditions, use .

    XtErrorMsgHandler XtAppSetErrorMsgHandler
       XtAppContext app_context
       XtErrorMsgHandler msg_handler

app_context

  Specifies the application context.

msg_handler

  Specifies the new fatal error procedure, which should not return.

returns a pointer to the previously installed high-level fatal error handler. The default high-level fatal error handler provided by the Intrinsics is named `_XtDefaultErrorMsg` and constructs a string from the error resource database and calls . Fatal error message handlers should not return. If one does, subsequent Intrinsics behavior is undefined.

To call the high-level error handler, use .

    void XtAppErrorMsg
       XtAppContext app_context
       const char * name
       const char * type
       const char * class
       const char * default
       String * params
       Cardinal * num_params

app_context

  Specifies the application context.

name

  Specifies the general kind of error.

type

  Specifies the detailed name of the error.

class

  Specifies the resource class.

default

  Specifies the default message to use if an error database entry is not found.

params

  Specifies a pointer to a list of values to be stored in the message.

num_params

  Specifies the number of entries in params.

The Intrinsics internal errors all have class “XtToolkitError”.

To register a procedure to be called on nonfatal error conditions, use .

    XtErrorMsgHandler XtAppSetWarningMsgHandler
       XtAppContext app_context
       XtErrorMsgHandler msg_handler

app_context

  Specifies the application context.

msg_handler

  Specifies the new nonfatal error procedure, which usually returns.

returns a pointer to the previously installed high-level warning handler. The default high-level warning handler provided by the Intrinsics is named `_XtDefaultWarningMsg` and constructs a string from the error resource database and calls .

To call the installed high-level warning handler, use .

    void XtAppWarningMsg
       XtAppContext app_context
       const char * name
       const char * type
       const char * class
       const char * default
       String * params
       Cardinal * num_params

app_context

  Specifies the application context.

name

  Specifies the general kind of error.

type

  Specifies the detailed name of the error.

class

  Specifies the resource class.

default

  Specifies the default message to use if an error database entry is not found.

params

  Specifies a pointer to a list of values to be stored in the message.

num_params

  Specifies the number of entries in params.

The Intrinsics internal warnings all have class “XtToolkitError”.

The low-level error and warning handler procedure pointers are of type .

    typedef void (*XtErrorHandler)
       String message

message

  Specifies the error message.

The error handler should display the message string in some appropriate fashion.

To register a procedure to be called on fatal error conditions, use .

    XtErrorHandler XtAppSetErrorHandler
       XtAppContext app_context
       XtErrorHandler handler

app_context

  Specifies the application context.

handler

  Specifies the new fatal error procedure, which should not return.

returns a pointer to the previously installed low-level fatal error handler. The default low-level error handler provided by the Intrinsics is `_XtDefaultError`. 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 Intrinsics behavior is undefined.

To call the installed fatal error procedure, use .

    void XtAppError
       XtAppContext app_context
       const char * message

app_context

  Specifies the application context.

message

  Specifies the message to be reported.

Most programs should use , not , to provide for customization and internationalization of error messages.

To register a procedure to be called on nonfatal error conditions, use .

    XtErrorHandler XtAppSetWarningHandler
       XtAppContext app_context
       XtErrorHandler handler

app_context

  Specifies the application context.

handler

  Specifies the new nonfatal error procedure, which usually returns.

returns a pointer to the previously installed low-level warning handler. The default low-level warning handler provided by the Intrinsics is `_XtDefaultWarning`. On POSIX-based systems, it prints the message to standard error and returns to the caller.

To call the installed nonfatal error procedure, use .

    void XtAppWarning
       XtAppContext app_context
       const char * message

app_context

  Specifies the application context.

message

  Specifies the nonfatal error message to be reported.

Most programs should use , not , to provide for customization and internationalization of warning messages.

## Setting WM_COLORMAP_WINDOWS

A client may set the value of the WM_COLORMAP_WINDOWS property on a widget's window by calling .

    void XtSetWMColormapWindows
       Widget widget
       Widget* list
       Cardinal count

widget

  Specifies the widget on whose window the WM_COLORMAP_WINDOWS property is stored. Must be of class Core or any subclass thereof.

list

  Specifies a list of widgets whose windows are potentially to be listed in the WM_COLORMAP_WINDOWS property.

count

  Specifies the number of widgets in list.

returns immediately if widget is not realized or if count is 0. Otherwise, constructs an ordered list of windows by examining each widget in list 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.

Finally, stores the resulting window list in the WM_COLORMAP_WINDOWS property on the specified widget's window. Refer to Section 4.1.8 in the Inter-Client Communication Conventions Manual for details of the semantics of the WM_COLORMAP_WINDOWS property.

## Finding File Names

The Intrinsics provide procedures to look for a file by name, allowing string substitutions in a list of file specifications. Two routines are provided for this: and . uses an arbitrary set of client-specified substitutions, and uses a set of standard substitutions corresponding to the X/Open Portability Guide language localization conventions. Most applications should use .

A string substitution is defined by a list of `Substitution` entries.

    typedef struct {
            char    match;
            String  substitution;
    } SubstitutionRec, *Substitution;

File name evaluation is handled in an operating-system-dependent fashion by an procedure.

    typedef Boolean (*XtFilePredicate)
       String filename

filename

  Specifies a potential filename.

A file predicate procedure is called with a string that is potentially a file name. It should return `True` if this string specifies a file that is appropriate for the intended use and `False` otherwise.

To search for a file using substitutions in a path list, use .

    char * XtFindFile
       const char * path
       Substitution substitutions
       Cardinal num_substitutions
       XtFilePredicate predicate

path

  Specifies a path of file names, including substitution characters.

substitutions

  Specifies a list of substitutions to make into the path.

num_substitutions

  Specifies the number of substitutions passed in.

predicate

  Specifies a procedure called to judge each potential file name, or NULL.

The path 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, looks through the specified substitutions for that character in the match field and, if found, replaces the percent and match characters with the string in the corresponding substitution field. A substitution 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, 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 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 `True`; this string is the return value for . If no string yields a `True` return from the predicate, returns NULL.

If the predicate parameter is NULL, an internal procedure that checks if the file exists, is readable, and is not a directory is used.

It is the responsibility of the caller to free the returned string using when it is no longer needed.

To search for a file using standard substitutions in a path list, use .

    char * XtResolvePathname
       Display *display
       const char * type
       const char * filename
       const char * suffix
       const char * path
       Substitution substitutions
       Cardinal num_substitutions
       XtFilePredicate predicate

display

  Specifies the display to use to find the language for language substitutions.

type

filename

suffix

  Specify values to substitute into the path.

path

  Specifies the list of file specifications, or NULL.

substitutions

  Specifies a list of additional substitutions to make into the path, or NULL.

num_substitutions

  Specifies the number of entries in substitutions.

predicate

  Specifies a procedure called to judge each potential file name, or NULL.

The substitutions specified by are determined from the value of the language string retrieved by for the specified display. To set the language for all applications specify “*xnlLanguage: lang” in the resource database. 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 Intrinsics make no interpretation of the parts other than to use them in substitutions as described below.

calls with the following substitutions in addition to any passed by the caller and returns the value returned by :

%N

  The value of the filename parameter, or the application's class name if filename is NULL.

%T

  The value of the type parameter.

%S

  The value of the suffix parameter.

%L

  The language string associated with the specified display.

%l

  The language part of the display's language string.

%t

  The territory part of the display's language string.

%c

  The codeset part of the display's language string.

%C

  The customization string retrieved from the resource database associated with display.

%D

  The value of the implementation-specific default path.

If a path is passed to , it is passed along to . If the path argument is NULL, the value of the XFILESEARCHPATH environment variable is passed to . If XFILESEARCHPATH is not defined, an implementation-specific default path is used that contains at least six entries. These entries must contain the following substitutions:

    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

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, `%N%S` is inserted between them.

The type 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”.

The suffix parameter is intended to be appended to the file name. Possible values might include “.txt”, “.dat”, and “.bm”.

A suggested value for the default path on POSIX-based systems is

       /usr/lib/X11/%L/%T/%N%C%S:/usr/lib/X11/%l/%T/%N%C%S:\
       /usr/lib/X11/%T/%N%C%S:/usr/lib/X11/%L/%T/%N%S:\
       /usr/lib/X11/%l/%T/%N%S:/usr/lib/X11/%T/%N%S

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 type parameter is used as a subdirectory of the language directory or of /usr/lib/X11, and suffix is appended to the file name.

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 XFILESEARCHPATH to

       %D:ourdir/%T/%N%C:ourdir/%T/%N

The customization string is obtained by querying the resource database currently associated with the display (the database returned by `XrmGetDatabase`) for the resource application_name.customization, class application_class.Customization, where application_name and application_class are the values returned by . If no value is specified in the database, the empty string is used.

It is the responsibility of the caller to free the returned string using when it is no longer needed.

## Hooks for External Agents

Applications may register functions that are called at a particular control points in the Intrinsics. These functions are intended to be used to provide notification of an “X Toolkit event”, 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 “hook registration” object.

To retrieve the hook registration widget, use .

    Widget XtHooksOfDisplay
       Display *display

display

  Specifies the desired display.

The class of this object is a private, implementation-dependent subclass of `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.

The following procedures can be called with the hook registration object as an argument:

- , , , , , , ,

- , `XtSuperclass`, , , `XtIsObject`, `XtIsRectObj`, `XtIsWidget`, `XtIsComposite`, `XtIsConstraint`, `XtIsShell`, `XtIsOverrideShell`, `XtIsWMShell`, `XtIsVendorShell`, `XtIsTransientShell`, `XtIsTopLevelShell`, `XtIsApplicationShell`, `XtIsSessionShell`

- , `XtParent`, ,

- , , ,

### Hook Object Resources

The resource names, classes, and representation types that are specified in the hook object resource list are:

Name | Class | Representation
--- | --- | ---
XtNcreateHook | XtCCallback | XtRCallback
XtNchangeHook | XtCCallback | XtRCallback
XtNconfigureHook | XtCCallback | XtRCallback
XtNgeometryHook | XtCCallback | XtRCallback
XtNdestroyHook | XtCCallback | XtRCallback
XtNshells | XtCReadOnly | XtRWidgetList
XtNnumShells | XtCReadOnly | XtRCardinal

Descriptions of each of these resources:

The XtNcreateHook callback list is called from: , , , , and their corresponding varargs versions.

The call_data parameter in a createHook callback may be cast to type `XtCreateHookData`.

    typedef struct {
            String   type;
            Widget   widget;
            ArgList  args;
            Cardinal num_args;
    } XtCreateHookDataRec, *XtCreateHookData;

The type is set to `XtHcreate`, widget is the newly created widget, and args and num_args are the arguments passed to the create function. The callbacks are called before returning from the create function.

The XtNchangeHook callback list is called from:

- ,

- , , ,

- ,

- , , `XtAddCallbacks,` ,

- , ,

- ,

- , ,

- , ,

The call_data parameter in a changeHook callback may be cast to type `XtChangeHookData`.

    typedef struct {
            String          type;
            Widget          widget;
            XtPointer       event_data;
            Cardinal        num_event_data;
    } XtChangeHookDataRec, *XtChangeHookData;

When the changeHook callbacks are called as a result of a call to or , type is set to `XtHsetValues`, widget is the new widget passed to the set_values procedure, and event_data may be cast to type `XtChangeHookSetValuesData`.

    typedef struct {
            Widget          old, req;
            ArgList         args;
            Cardinal        num_args;
    } XtChangeHookSetValuesDataRec, *XtChangeHookSetValuesData;

The old, req, args, and num_args 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.

When the changeHook callbacks are called as a result of a call to or , type is set to `XtHmanageChildren`, widget is the parent, event_data may be cast to type WidgetList and is the list of children being managed, and num_event_data is the length of the widget list. The callbacks are called after the children have been managed.

When the changeHook callbacks are called as a result of a call to or , type is set to `XtHunmanageChildren`, widget is the parent, event_data may be cast to type WidgetList and is a list of the children being unmanaged, and num_event_data is the length of the widget list. The callbacks are called after the children have been unmanaged.

The changeHook callbacks are called twice as a result of a call to , once after unmanaging and again after managing. When the callbacks are called the first time, type is set to `XtHunmanageSet`, widget is the parent, event_data may be cast to type WidgetList and is a list of the children being unmanaged, and num_event_data is the length of the widget list. When the callbacks are called the second time, the type is set to `XtHmanageSet`, widget is the parent, event_data may be cast to type WidgetList and is a list of the children being managed, and num_event_data is the length of the widget list.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHrealizeWidget` and widget is the widget being realized. The callbacks are called after the widget has been realized.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHunrealizeWidget`, and widget is the widget being unrealized. The callbacks are called after the widget has been unrealized.

When the changeHook callbacks are called as a result of a call to , type is set to `XtHaddCallback`, widget is the widget to which the callback is being added, and event_data 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.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHaddCallbacks`, widget is the widget to which the callbacks are being added, and event_data 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.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHremoveCallback`, widget is the widget from which the callback is being removed, and event_data 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.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHremoveCallbacks`, widget is the widget from which the callbacks are being removed, and event_data 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.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHremoveAllCallbacks` and widget is the widget from which the callbacks are being removed. The callbacks are called after the callbacks have been removed from the widget.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHaugmentTranslations` and widget is the widget whose translations are being modified. The callbacks are called after the widget's translations have been modified.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHoverrideTranslations` and widget is the widget whose translations are being modified. The callbacks are called after the widget's translations have been modified.

When the changeHook callbacks are called as a result of a call to , The type is `XtHuninstallTranslations` and widget is the widget whose translations are being uninstalled. The callbacks are called after the widget's translations have been uninstalled.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHsetKeyboardFocus` and event_data may be cast to type Widget and is the value of the descendant argument passed to . The callbacks are called before returning from .

When the changeHook callbacks are called as a result of a call to , type is set to `XtHsetWMColormapWindows`, event_data may be cast to type WidgetList and is the value of the list argument passed to , and num_event_data is the length of the list. The callbacks are called before returning from .

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHsetMappedWhenManaged` and event_data may be cast to type Boolean and is the value of the mapped_when_managed argument passed to . The callbacks are called after setting the widget's mapped_when_managed field and before realizing or unrealizing the widget.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHmapWidget` and widget is the widget being mapped. The callbacks are called after mapping the widget.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHunmapWidget` and widget is the widget being unmapped. The callbacks are called after unmapping the widget.

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHpopup`, widget is the widget being popped up, and event_data may be cast to type XtGrabKind and is the value of the grab_kind argument passed to . The callbacks are called before returning from .

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHpopupSpringLoaded` and widget is the widget being popped up. The callbacks are called before returning from .

When the changeHook callbacks are called as a result of a call to , the type is set to `XtHpopdown` and widget is the widget being popped down. The callbacks are called before returning from .

A widget set that exports interfaces that change application state without employing the Intrinsics library should invoke the change hook itself. This is done by:

            XtCallCallbacks(XtHooksOfDisplay(dpy), XtNchangeHook, call_data);

The XtNconfigureHook callback list is called any time the Intrinsics move, resize, or configure a widget and when is called.

The call_data parameter may be cast to type `XtConfigureHookData.`

    typedef struct {
            String          type;
            Widget          widget;
            XtGeometryMask  changeMask;
            XWindowChanges  changes;
    } XtConfigureHookDataRec, *XtConfigureHookData;

When the configureHook callbacks are called, the type is `XtHconfigure`, widget is the widget being configured, and changeMask and changes reflect the changes made to the widget. The callbacks are called after changes have been made to the widget.

The XtNgeometryHook callback list is called from and once before and once after geometry negotiation occurs.

The call_data parameter may be cast to type `XtGeometryHookData`.

    typedef struct {
            String          type;
            Widget          widget;
            XtWidgetGeometry* request;
            XtWidgetGeometry* reply;
            XtGeometryResult result;
    } XtGeometryHookDataRec, *XtGeometryHookData;

When the geometryHook callbacks are called prior to geometry negotiation, the type is `XtHpreGeometry`, widget is the widget for which the request is being made, and request is the requested geometry. When the geometryHook callbacks are called after geometry negotiation, the type is `XtHpostGeometry`, widget is the widget for which the request was made, request is the requested geometry, reply is the resulting geometry granted, and result is the value returned from the geometry negotiation.

The XtNdestroyHook callback list is called when a widget is destroyed. The call_data parameter may be cast to type `XtDestroyHookData`.

    typedef struct {
            String type;
            Widget widget;
    } XtDestroyHookDataRec, *XtDestroyHookData;

When the destroyHook callbacks are called as a result of a call to , the type is `XtHdestroy` and widget is the widget being destroyed. The callbacks are called upon completion of phase one destroy for a widget.

The XtNshells and XtNnumShells are read-only resources that report a list of all parentless shell widgets associated with a display.

Clients who use these hooks must exercise caution in calling Intrinsics functions in order to avoid recursion.

### Querying Open Displays

To retrieve a list of the Displays associated with an application context, use .

    void XtGetDisplays
       XtAppContext app_context
       Display ***dpy_return
       Cardinal *num_dpy_return

app_context

  Specifies the application context.

dpy_return

  Returns a list of open Display connections in the specified application context.

num_dpy_return

  Returns the count of open Display connections in dpy_return.

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 .