XGetWindowProperty(3) XLIB FUNCTIONS XGetWindowProperty(3)
NAME
XGetWindowProperty, XListProperties, XChangeProperty, XRotateWindow-
Properties, 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_re-
turn);
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 proper-
ties[], 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 prop-
erty if a partial read was performed.
data Specifies the property data.
delete Specifies a Boolean value that determines whether the prop-
erty 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 cor-
rectly 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 XChange-
Property.
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 PropMod-
eReplace, PropModePrepend, or PropModeAppend.
nelements Specifies the number of elements of the specified data for-
mat.
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 ar-
ray. If the returned format is 16, the returned data is rep-
resented 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 applica-
tion 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 prop-
erty; 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. XGetWin-
dowProperty 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 argu-
ment 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_re-
turn. It also ignores the delete argument. The nitems_return ar-
gument is empty.
• If the specified property exists and either you assign AnyProper-
tyType to the req_type argument or the specified type matches the
actual property type, XGetWindowProperty returns the actual prop-
erty 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 (index-
ing 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 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 ele-
ments. 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 er-
rors.
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 func-
tion, use XFree.
XListProperties can generate a BadWindow error.
The XChangeProperty function alters the property for the specified win-
dow 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
property value and stores the new data.
• If mode is PropModePrepend or PropModeAppend, XChangeProperty in-
serts 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. Proper-
ties 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 depend-
ing on the amount of memory the server has available. (If there is in-
sufficient 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 nposi-
tions, 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 win-
dow, 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 1.8.4 XGetWindowProperty(3)
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