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