XGetWindowProperty(3X11) XLIB FUNCTIONS XGetWindowProperty(3X11)
NAME
XGetWindowProperty, XListProperties, XChangeProperty, XRota-
teWindowProperties, XDeleteProperty - obtain and change win-
dow properties
SYNTAX
int XGetWindowProperty(Display *display, Window w, Atom pro-
perty, 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 for-
mat, int mode, 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 pro-
perty);
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. Pos-
sible 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.
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XGetWindowProperty(3X11) XLIB FUNCTIONS XGetWindowProperty(3X11)
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 PropModeAp-
pend.
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 interpret the type but simply passes it
back to an application that later calls XGetWin-
dowProperty.
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
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XGetWindowProperty(3X11) XLIB FUNCTIONS XGetWindowProperty(3X11)
bytes remaining to be read in the property; and a pointer to
the data actually returned. XGetWindowProperty sets the
return arguments as follows:
+ If the specified property does not exist for the speci-
fied 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 argu-
ment. The nitems_return argument is empty.
+ If the specified property exists and either you assign
AnyPropertyType to the req_type argument or the speci-
fied type matches the actual property type, XGetWin-
dowProperty 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 pro-
perty (indexing from zero), and its length in bytes is
L. If the value for long_offset causes L to be nega-
tive, 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 ele-
ments.
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XGetWindowProperty(3X11) XLIB FUNCTIONS XGetWindowProperty(3X11)
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 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 Pro-
pertyNotify event on that window. XChangeProperty performs
the following:
+ If mode is PropModeReplace, XChangeProperty discards
the previous property 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.
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XGetWindowProperty(3X11) XLIB FUNCTIONS XGetWindowProperty(3X11)
(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 proper-
ties 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 nposi-
tions). If npositions mod N is nonzero, the X server gen-
erates 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 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 argument, the full range
defined by the argument's type is accepted. Any
argument defined as a set of alternatives can gen-
erate 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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