.. _mpi_type_create_keyval:


MPI_Type_create_keyval
======================

.. include_body

:ref:`MPI_Type_create_keyval` - Generates a new attribute key for caching
on data types.


SYNTAX
------


C Syntax
^^^^^^^^

.. code-block:: c

   #include <mpi.h>

   int MPI_Type_create_keyval(MPI_Type_copy_attr_function *type_copy_attr_fn,
   	MPI_Type_delete_attr_function *type_delete_attr_fn,
   	int *type_keyval, void *extra_state)


Fortran Syntax (see FORTRAN 77 NOTES)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. code-block:: fortran

   USE MPI
   ! or the older form: INCLUDE 'mpif.h'
   MPI_TYPE_CREATE_KEYVAL(TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN,
   		TYPE_KEYVAL, EXTRA_STATE, IERROR)
   	EXTERNAL TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN
   	INTEGER	TYPE_KEYVAL, IERROR
   	INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE


Fortran 2008 Syntax
^^^^^^^^^^^^^^^^^^^

.. code-block:: fortran

   USE mpi_f08
   MPI_Type_create_keyval(type_copy_attr_fn, type_delete_attr_fn, type_keyval,
   		extra_state, ierror)
   	PROCEDURE(MPI_Type_copy_attr_function) :: type_copy_attr_fn
   	PROCEDURE(MPI_Type_delete_attr_function) :: type_delete_attr_fn
   	INTEGER, INTENT(OUT) :: type_keyval
   	INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: extra_state
   	INTEGER, OPTIONAL, INTENT(OUT) :: ierror


INPUT PARAMETERS
----------------
* ``type_copy_attr_fn``: Copy callback function for *type_keyval* (function).
* ``type_delete_attr_fn``: Delete callback function for *type_keyval* (function).
* ``extra_state``: Extra state for callback functions.

OUTPUT PARAMETERS
-----------------
* ``type_keyval``: Key value for future access (integer).
* ``IERROR``: Fortran only: Error status (integer).

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

:ref:`MPI_Type_create_keyval` generates a new attribute key for caching on data
types. This routine partially replaces :ref:`MPI_Keyval_create`.

The argument *type_copy_attr_fn* may be specified as
MPI_TYPE_NULL_COPY_FN or MPI_TYPE_DUP_FN from C or Fortran.
MPI_TYPE_NULL_COPY_FN is a function that does nothing other than
returning *flag* = 0 and MPI_SUCCESS. MPI_TYPE_DUP_FN is a simple-minded
copy function that sets *flag* = 1, returns the value of
*attribute_val_in* in *attribute_val_out*, and returns MPI_SUCCESS.

The argument *type_delete_attr_fn* may be specified as
MPI_TYPE_NULL_DELETE_FN from C or Fortran. MPI_TYPE_NULL_DELETE_FN is a
function that does nothing beyond returning MPI_SUCCESS. The C callback
functions are:

::

   typedef int MPI_Type_copy_attr_function(MPI_Datatype oldtype,
               int type_keyval, void *extra_state, void *attribute_val_in,
               void *attribute_val_out, int *flag);

and

::

   typedef int MPI_Type_delete_attr_function(MPI_Datatype type, int type_keyval,
                void *attribute_val, void *extra_state);

The Fortran callback functions are:

.. code-block:: fortran

   SUBROUTINE TYPE_COPY_ATTR_FN(OLDTYPE, TYPE_KEYVAL, EXTRA_STATE,
                ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR)
       INTEGER OLDTYPE, TYPE KEYVAL, IERROR
       INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE,
           ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT
       LOGICAL FLAG

and

::

   SUBROUTINE TYPE_DELETE_ATTR_FN(TYPE, TYPE_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE,
                IERROR)
       INTEGER TYPE, TYPE_KEYVAL, IERROR
       INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE VAL, EXTRA_STATE


FORTRAN 77 NOTES
----------------

The MPI standard prescribes portable Fortran syntax for the
*EXTRA_STATE* argument only for Fortran 90. FORTRAN 77 users may use the
non-portable syntax

::

        INTEGER*MPI_ADDRESS_KIND EXTRA_STATE

where MPI_ADDRESS_KIND is a constant defined in mpif.h and gives the
length of the declared integer in bytes.


ERRORS
------

Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument.

Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
:ref:`MPI_Comm_set_errhandler`; the predefined error handler MPI_ERRORS_RETURN
may be used to cause error values to be returned. Note that MPI does not
guarantee that an MPI program can continue past an error.


.. seealso::
   :ref:`MPI_Type_free_keyval`
