XGetWindowProperty(XS) X Version 11 (Release 5) XGetWindowProperty(XS)
6 January 1993
Name
XGetWindowProperty - obtain and change window properties
Syntax
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
actualformatreturn
Returns the actual format of the property.
actualtypereturn
Returns the atom identifier that defines the actual type
of the property.
bytesafterreturn
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 pro-
perty 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.
longlength Specifies the length in 32-bit multiples of the data to be
retrieved.
longoffset 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 PropMo-
deReplace, PropModePrepend, or PropModeAppend.
nelements Specifies the number of elements of the specified data
format.
nitemsreturn Returns the actual number of 8-bit, 16-bit, or 32-bit
items stored in the propreturn data.
numprop Specifies the length of the properties array.
numpropreturn
Returns the length of the properties array.
npositions Specifies the rotation amount.
propreturn Returns the data in the specified format.
property Specifies the property name.
properties Specifies the array of properties that are to be rotated.
reqtype 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 appli-
cation 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 pro-
perty; 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 actualtypereturn and the value
zero to actualformatreturn and bytesafterreturn. The
nitemsreturn 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
actualtypereturn, the actual property format (never zero) to
actualformatreturn, and the property length in bytes (even if the
actualformatreturn is 16 or 32) to bytesafterreturn. It also
ignores the delete argument. The nitemsreturn argument is empty.
+ If the specified property exists and either you assign AnyPropertyType
to the reqtype argument or the specified type matches the actual pro-
perty type, XGetWindowProperty returns the actual property type to
actualtypereturn and the actual property format (never zero) to
actualformatreturn. It also returns a value to bytesafterreturn
and nitemsreturn, 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
longoffset causes L to be negative, a ``BadValue'' error results.
The value of bytesafterreturn is A, giving the number of trailing
unread bytes in the stored property.
XGetWindowProperty always allocates one extra byte in propreturn (even
if the property is zero length) and sets it to ASCII null so that simple
properties consisting of characters do not have to be copied into yet
another string before use. If delete is True and bytesafterreturn is
zero, XGetWindowProperty 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 ``BadWin-
dow'' errors.
The XListProperties function returns a pointer to an array of atom pro-
perties 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 win-
dow. XChangeProperty performs the following:
+ If mode is PropModeReplace, XChangeProperty discards the previous pro-
perty 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.
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 of Xlib - C Language X Inter-
face. 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 numprop property names in the list,
then the value associated with property name I becomes the value associ-
ated 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 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 ``BadAtom'' or ``BadMatch'' error results, no pro-
perties 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 Win-
dow.
See also
XFree(XS), XInternAtom(XS)
Xlib - C Language X Interface