XGetWindowProperty(3) XLIB FUNCTIONS XGetWindowProperty(3)

NAME

XGetWindowProperty, XListProperties, XChangeProperty,
XRotateWindowProperties, XDeleteProperty - obtain and change window
properties

SYNTAX

int XGetWindowProperty(Display *display, Window w, Atom property,
long long_offset, long 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 *display, Window w, int
*num_prop_return);

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

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

int XDeleteProperty(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
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.

npositions
Specifies the rotation amount.

prop_return
Returns the data in the specified format. 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 array of short int type and should be cast
to that type to obtain the elements. If the returned
format is 32, the property data will be stored as an array
of longs (which in a 64-bit application will be 64-bit
values that are padded in the upper 4 bytes).

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 (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 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.

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(3), XInternAtom(3)
Xlib - C Language X Interface

X Version 11 libX11 1.8.10 XGetWindowProperty(3)