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.
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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.
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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
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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
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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
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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 ALSOXFree(3X11), XInternAtom(3X11)
Xlib - C Language X Interface
X Version 11 Release 6.4 6
