XGetWindowProperty man page on BSDi

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XGetWindowProperty(3X11)  XLIB FUNCTIONS XGetWindowProperty(3X11)

NAME
       XGetWindowProperty, XListProperties, XChangeProperty, XRo-
       tateWindowProperties, XDeleteProperty - obtain and change
       window properties

SYNTAX
       int XGetWindowProperty(display, w, property, long_offset,
       long_length, delete, req_type,
			       actual_type_return,
       actual_format_return, nitems_return, bytes_after_return,
			       prop_return)
	     Display *display;
	     Window w;
	     Atom property;
	     long long_offset, long_length;
	     Bool delete;
	     Atom req_type;
	     Atom *actual_type_return;
	     int *actual_format_return;
	     unsigned long *nitems_return;
	     unsigned long *bytes_after_return;
	     unsigned char **prop_return;

       Atom *XListProperties(display, w, num_prop_return)
	     Display *display;
	     Window w;
	     int *num_prop_return;

       XChangeProperty(display, w, property, type, format, mode,
       data, nelements)
	     Display *display;
	     Window w;
	     Atom property, type;
	     int format;
	     int mode;
	     unsigned char *data;
	     int nelements;

       XRotateWindowProperties(display, w, properties, num_prop,
       npositions)
	     Display *display;
	     Window w;
	     Atom properties[];
	     int num_prop;
	     int npositions;

       XDeleteProperty(display, w, property)
	     Display *display;
	     Window w;
	     Atom property;

ARGUMENTS
       actual_format_return
		 Returns the actual format of the property.

X Version 11		Release 6.4				1

XGetWindowProperty(3X11)  XLIB FUNCTIONS XGetWindowProperty(3X11)

       actual_type_return
		 Returns the atom identifier  that defines the
		 actual type of the property.

       bytes_after_return
		 Returns the number of bytes remaining to be read
		 in the property if a partial read was performed.

       data	Specifies the property data.

       delete	Specifies a Boolean value that determines
		 whether the property is deleted.

       display	Specifies the connection to the X server.

       format	Specifies whether the data should be viewed as a
		 list of 8-bit, 16-bit, or 32-bit quantities.
		 Possible values are 8, 16, and 32.  This infor-
		 mation allows the X server to correctly perform
		 byte-swap operations as necessary.  If the for-
		 mat is 16-bit or 32-bit, you must explicitly
		 cast your data pointer to an (unsigned char *)
		 in the call to XChangeProperty.

       long_length
		 Specifies the length in 32-bit multiples of the
		 data to be retrieved.

       long_offset
		 Specifies the offset in the specified property
		 (in 32-bit quantities) where the data is to be
		 retrieved.

       mode	Specifies the mode of the operation.  You can
		 pass PropModeReplace, PropModePrepend, or
		 PropModeAppend.

       nelements Specifies the number of elements of the speci-
		 fied data format.

       nitems_return
		 Returns the actual number of 8-bit, 16-bit, or
		 32-bit items stored in the prop_return data.

       num_prop Specifies the length of the properties array.

       num_prop_return
		 Returns the length of the properties array.

       npositions
		 Specifies the rotation amount.

       prop_return
		 Returns the data in the specified format.

X Version 11		Release 6.4				2

XGetWindowProperty(3X11)  XLIB FUNCTIONS XGetWindowProperty(3X11)

       property Specifies the property name.

       properties
		 Specifies the array of properties that are to be
		 rotated.

       req_type Specifies the atom identifier associated with
		 the property type or AnyPropertyType.

       type	Specifies the type of the property.  The X
		 server does not interpret the type but simply
		 passes it back to an application that later
		 calls XGetWindowProperty.

       w	 Specifies the window whose property you want to
		 obtain, change, rotate or delete.

DESCRIPTION
       The XGetWindowProperty function returns the actual type of
       the property; the actual format of the property; the num-
       ber of 8-bit, 16-bit, or 32-bit items transferred; the
       number of bytes remaining to be read in the property; and
       a pointer to the data actually returned. XGetWindowProp-
       erty sets the return arguments as follows:

       o    If the specified property does not exist for the
	    specified window, XGetWindowProperty returns None to
	    actual_type_return and the value zero to actual_for-
	    mat_return and bytes_after_return.	The nitems_return
	    argument is empty.	In this case, the delete argument
	    is ignored.

       o    If the specified property exists but its type does
	    not match the specified type, XGetWindowProperty
	    returns the actual property type to
	    actual_type_return, the actual property format (never
	    zero) to actual_format_return, and the property
	    length in bytes (even if the actual_format_return is
	    16 or 32) to bytes_after_return.  It also ignores the
	    delete argument.  The nitems_return argument is
	    empty.

       o    If the specified property exists and either you
	    assign AnyPropertyType to the req_type argument or
	    the specified type matches the actual property type,
	    XGetWindowProperty returns the actual property type
	    to actual_type_return and the actual property format
	    (never zero) to actual_format_return.  It also
	    returns a value to bytes_after_return and
	    nitems_return, by defining the following values:

		 N = actual length of the stored property in bytes
		      (even if the format is 16 or 32)
		 I = 4 * long_offset

X Version 11		Release 6.4				3

XGetWindowProperty(3X11)  XLIB FUNCTIONS XGetWindowProperty(3X11)

		 T = N - I
		 L = MINIMUM(T, 4 * long_length)
		 A = N - (I + L)

	    The returned value starts at byte index I in the
	    property (indexing from zero), and its length in
	    bytes is L. If the value for long_offset causes L to
	    be negative, a BadValue error results.  The value of
	    bytes_after_return is A, giving the number of trail-
	    ing unread bytes in the stored property.

       If the returned format is 8, the returned data is repre-
       sented as a char array.	If the returned format is 16, the
       returned data is represented as a short array and should
       be cast to that type to obtain the elements.  If the
       returned format is 32, the returned data is represented as
       a long array and should be cast to that type to obtain the
       elements.

       XGetWindowProperty always allocates one extra byte in
       prop_return (even if the property is zero length) and sets
       it to zero so that simple properties consisting of charac-
       ters do not have to be copied into yet another string
       before use.

       If delete is True and bytes_after_return is zero, XGetWin-
       dowProperty deletes the property from the window and gen-
       erates a PropertyNotify event on the window.

       The function returns Success if it executes successfully.
       To free the resulting data, use XFree.

       XGetWindowProperty can generate BadAtom, BadValue, and
       BadWindow errors.

       The XListProperties function returns a pointer to an array
       of atom properties that are defined for the specified win-
       dow or returns NULL if no properties were found. To free
       the memory allocated by this function, use XFree.

       XListProperties can generate a BadWindow error.

       The XChangeProperty function alters the property for the
       specified window and causes the X server to generate a
       PropertyNotify event on that window.  XChangeProperty per-
       forms the following:

       o    If mode is PropModeReplace, XChangeProperty discards
	    the previous property value and stores the new data.

       o    If mode is PropModePrepend or PropModeAppend,
	    XChangeProperty inserts the specified data before the
	    beginning of the existing data or onto the end of the
	    existing data, respectively.  The type and format

X Version 11		Release 6.4				4

XGetWindowProperty(3X11)  XLIB FUNCTIONS XGetWindowProperty(3X11)

	    must match the existing property value, or a BadMatch
	    error results.  If the property is undefined, it is
	    treated as defined with the correct type and format
	    with zero-length data.

       If the specified format is 8, the property data must be a
       char array.  If the specified format is 16, the property
       data must be a short array.  If the specified format is
       32, the property data must be a long array.

       The lifetime of a property is not tied to the storing
       client.	Properties remain until explicitly deleted, until
       the window is destroyed, or until the server resets.  For
       a discussion of what happens when the connection to the X
       server is closed, see section 2.6.  The maximum size of a
       property is server dependent and can vary dynamically
       depending on the amount of memory the server has avail-
       able.  (If there is insufficient space, a BadAlloc error
       results.)

       XChangeProperty can generate BadAlloc, BadAtom, BadMatch,
       BadValue, and BadWindow errors.

       The XRotateWindowProperties function allows you to rotate
       properties on a window and causes the X server to generate
       PropertyNotify events.  If the property names in the prop-
       erties array are viewed as being numbered starting from
       zero and if there are num_prop property names in the list,
       then the value associated with property name I becomes the
       value associated with property name (I + npositions) mod N
       for all I from zero to N - 1.  The effect is to rotate the
       states by npositions places around the virtual ring of
       property names (right for positive npositions, left for
       negative npositions).  If npositions mod N is nonzero, the
       X server generates a PropertyNotify event for each prop-
       erty in the order that they are listed in the array.  If
       an atom occurs more than once in the list or no property
       with that name is defined for the window, a BadMatch error
       results. If a BadAtom or BadMatch error results, no prop-
       erties are changed.

       XRotateWindowProperties can generate BadAtom, BadMatch,
       and BadWindow errors.

       The XDeleteProperty function deletes the specified prop-
       erty only if the property was defined on the specified
       window and causes the X server to generate a PropertyNo-
       tify event on the window unless the property does not
       exist.

       XDeleteProperty can generate BadAtom and BadWindow errors.

DIAGNOSTICS
       BadAlloc The server failed to allocate the requested

X Version 11		Release 6.4				5

XGetWindowProperty(3X11)  XLIB FUNCTIONS XGetWindowProperty(3X11)

		 resource or server memory.

       BadAtom	A value for an Atom argument does not name a
		 defined Atom.

       BadValue Some numeric value falls outside the range of
		 values accepted by the request.  Unless a spe-
		 cific range is specified for an argument, the
		 full range defined by the argument's type is
		 accepted.  Any argument defined as a set of
		 alternatives can generate this error.

       BadWindow A value for a Window argument does not name a
		 defined Window.

SEE ALSO
       XFree(3X11), XInternAtom(3X11)
       Xlib - C Language X Interface

X Version 11		Release 6.4				6

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