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<TITLE>XGetWindowProperty</TITLE>
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XGetWindowProperty(3X11)       XLIB FUNCTIONS	     XGetWindowProperty(3X11)



NAME
  XGetWindowProperty, XListProperties, XChangeProperty, XRotateWindowProper-
  ties, 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.

  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 information allows the X server to correctly perform byte-
	    swap operations as necessary.  If the format 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 quanti-
	    ties) where the data is to be retrieved.

  mode	    Specifies the mode of the operation.  You can pass PropModeRe-
	    place, PropModePrepend, or PropModeAppend.

  nelements Specifies the number of elements of the specified 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.

  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 inter-
	    pret 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 number of 8-bit, 16-bit, or 32-bit
  items transferred; the number of bytes remaining to be read in the pro-
  perty; and a pointer to the data actually returned.  XGetWindowProperty
  sets the return arguments as follows:

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

  +    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.

  +    If the specified property exists and either you assign AnyPropertyType
       to the req_type argument or the specified type matches the actual pro-
       perty 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
	       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 trailing unread
       bytes in the stored property.

  If the returned format is 8, the returned data is represented 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 characters do not have to be copied into yet another string
  before use.

  If delete is True and bytes_after_return is zero, XGetWindowProperty
  deletes the property from the window and generates 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 proper-
  ties that are defined for the specified window or returns NULL if no pro-
  perties 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 performs the following:

  +    If mode is PropModeReplace, XChangeProperty discards the previous pro-
       perty value and stores the new data.

  +    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 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 available.  (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 properties array are viewed as being numbered start-
  ing 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 nposi-
  tions).  If npositions mod N is nonzero, the X server generates a Proper-
  tyNotify event for each property 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 BadA-
  tom or BadMatch error results, no properties are changed.

  XRotateWindowProperties can generate BadAtom, BadMatch, and BadWindow
  errors.

  The XDeleteProperty function deletes the specified property only if the
  property was defined on the specified window and causes the X server to
  generate a PropertyNotify 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 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 specific range is specified for an argu-
	    ment, 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































































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