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XGetWindowProperty(3X11)
X11R6
NAME
XGetWindowProperty, XListProperties, XChangeProperty,
XRotateWindowProperties, XDeleteProperty - obtain and change window
properties
SYNOPSIS
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.
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.
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:
· 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.
· 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.
· 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:
· 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. (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(3X11), XInternAtom(3X11)
Xlib -- C Language X Interface
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