XGetWindowProperty(3X1Version 11 (ReleaseXGetWindowProperty(3X11)
NAME
XGetWindowProperty, XListProperties, XChangeProperty,
XRotateWindowProperties, 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
Page 1 (printed 7/20/06)
XGetWindowProperty(3X1Version 11 (ReleaseXGetWindowProperty(3X11)
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 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 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.
Page 2 (printed 7/20/06)
XGetWindowProperty(3X1Version 11 (ReleaseXGetWindowProperty(3X11)
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 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 number
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. XGetWindowProperty 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_format_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
Page 3 (printed 7/20/06)
XGetWindowProperty(3X1Version 11 (ReleaseXGetWindowProperty(3X11)
(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 properties that are defined for the specified window
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
Page 4 (printed 7/20/06)
XGetWindowProperty(3X1Version 11 (ReleaseXGetWindowProperty(3X11)
PropertyNotify event on that window. XChangeProperty
performs 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 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 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 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 BadAtom or BadMatch error results, no properties are
changed.
XRotateWindowProperties can generate BadAtom, BadMatch, and
BadWindow errors.
Page 5 (printed 7/20/06)
XGetWindowProperty(3X1Version 11 (ReleaseXGetWindowProperty(3X11)
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 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
Page 6 (printed 7/20/06)
