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.
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