Provided by: libx11-doc_1.6.9-2ubuntu1.6_all 
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, 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:
• 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(3), XInternAtom(3)
Xlib - C Language X Interface