File: XIChangeProperty.txt

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XICHANGEPROPERTY(libmansuffix)
==============================

NAME
----

   XIChangeProperty, XIGetProperty, XIDeleteProperty - change, retrieve
   or delete a device's property.

SYNOPSIS
--------

    #include <X11/extensions/XInput2.h>

    void XIChangeProperty( Display* dpy,
                           int deviceid,
                           Atom property,
                           Atom type,
                           int format,
                           int mode,
                           unsigned char *data,
                           int num_items)

   void XIDeleteProperty( Display *dpy,
                          int deviceid,
                          Atom property)

   Status XIGetProperty( Display *dpy,
                         int deviceid,
                         Atom property,
                         long offset,
                         long length,
                         Bool delete_property,
                         Atom type,
                         Atom *type_return,
                         int *format_return,
                         unsigned long *num_items_return,
                         unsigned long *bytes_after_return,
                         unsigned char **data)

   bytes_after_return
          Returns the number of bytes remaining to be read in the prop-
          erty if a partial read was performed.

   data
          Specifies the property data.

   display
          Specifies the connection to the X server.
    
   delete_property
          Specifies a Boolean value that determines whether the property
          is to be deleted.

   deviceid
          The device to list the properties for.

   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 
          XIChangeProperty.

   format_return
          Returns the actual format of the property.

   length 
          Specifies the length in 32-bit multiples of the data to be
          retrieved.

   offset
          Specifies the offset in the specified property (in 32-bit
          quantities) where the data is to be retrieved.

   mode
          One of PropModeAppend, PropModePrepend or PropModeReplace.

   num_items
          Number of items in data in the format specified.

   nitems_return
          Returns the actual number of 8-bit, 16-bit, or 32-bit items
          stored in data.

   property
          Specifies the property name.

   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 XIGetProperty.

   type_return
          Returns the atom identifier that defines the actual type of
          the property.

DESCRIPTION
-----------

The XIGetProperty 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.
XIGetProperty sets the return arguments as follows:

   - If the specified property does not exist for the specified device,
   XIGetProperty 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, XIGetProperty 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, XIGetProperty 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 = length of the stored property in bytes
   I = 4 * offset
   T = N - I
   L = MINIMUM(T, 4 * 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 uint16_t array and should be cast to that type to obtain the ele-
ments.  If the returned format is 32, the returned data is represented
as a uint32_t array and should be cast to that type to obtain the elements.

XIGetProperty 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, XIGetProperty
deletes the property from the window and generates an XIPropertyNotify
event on the window.

The function returns Success if it executes successfully.  To free the
resulting data, use XFree.

XIGetProperty can generate BadAtom, BadValue, and BadWindow
errors.

The XIChangeProperty function alters the property for the specified device
and causes the X server to generate a XIPropertyNotify event for that
device.  XIChangeProperty performs the following:

- If mode is PropModeReplace, XIChangeProperty 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 uint16_t array.
If the specified format is 32, the property data must be a uint32_t array.

The lifetime of a property is not tied to the storing client. 
Properties remain until explicitly deleted, until the device is removed, 
or until the server resets.  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.)

XIChangeProperty can generate BadAlloc, BadAtom, BadMatch, BadValue, and
BadDevice errors.

The XIDeleteProperty function deletes the specified property only if the
property was defined on the specified device and causes the X server to
generate a XIPropertyNotify event for the device unless the property does
not exist.

XIDeleteProperty can generate BadAtom and BadDevice 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.

BadDevice
       An invalid device was specified. The device does not
       exist.

BadAtom
       An invalid property was specified. The property does not
       exist.

SEE ALSO
--------

XIListProperties(libmansuffix)