XGetWindowProperty

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;

Arguments

display	Specifies the connection to the X server.
w	Specifies the window whose property you want to obtain.
property	Specifies the property name.
long_offset	Specifies the offset in the specified property (in 32-bit quantities) where the data is to be retrieved.
long_length	Specifies the length in 32-bit multiples of the data to be retrieved.
delete	Specifies a Boolean value that determines whether the property is deleted.
req_type	Specifies the atom identifier associated with the property type or AnyPropertyType.
actual_type_return	Returns the atom identifier that defines the actual type of the property.
actual_format_return	Returns the actual format of the property.
nitems_return	Returns the actual number of 8-bit, 16-bit, or 32-bit items stored in the prop_return data.
bytes_after_return	Returns the number of bytes remaining to be read in the property if a partial read was performed.
prop_return	Returns the data in the specified format.

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.

Diagnostics

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

XChangeProperty(), XDeleteProperty(), XListProperties(), XRotateWindowProperties(), "Obtaining and Changing Window Properties"

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Christophe Tronche, [email protected]