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 NAME
       MPI_Comm_create_keyval - Generates a new attribute key.
SYNTAX
 C Syntax
       #include <mpi.h>
       int MPI_Comm_create_keyval(MPI_Comm_copy_attr_function
            *comm_copy_attr_fn, MPI_Comm_delete_attr_function
            *comm_delete_attr_fn, int *comm_keyval,
            void *extra_state)
Fortran Syntax (see FORTRAN 77 NOTES)
       INCLUDE 'mpif.h'
       MPI_COMM_CREATE_KEYVAL(COMM_COPY_ATTR_FN, COMM_DELETE_ATTR_FN,
            COMM_KEYVAL, EXTRA_STATE, IERROR)
           EXTERNAL COMM_COPY_ATTR_FN, COMM_DELETE_ATTR_FN
           INTEGER COMM_KEYVAL, IERROR
           INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
C++ Syntax
       #include <mpi.h>
       static in MPI::Comm::Create_keyval(MPI::Comm::Copy_attr_function*
            comm_copy_attr_fn,
            MPI::Comm::Delete_attr_function* comm_delete_attr_fn,
            void* extra_state)
INPUT PARAMETERS
       comm_copy_attr_fn
                 Copy callback function for comm_keyval (function).
       comm_delete_attr_fn
                 Delete callback function for comm_keyval (function).
       extra_state
                 Extra state for callback functions.
OUTPUT PARAMETER
       comm_keyval
                 Key value for future access (integer).
       IERROR    Fortran only: Error status (integer).
DESCRIPTION
       This  function  replaces  MPI_Keyval_create, the use of which is depre-
       cated. The C binding is identical. The Fortran binding differs in  that
       extra_state  is  an  address-sized  integer.  Also, the copy and delete
       callback functions have  Fortran  bindings  that  are  consistent  with
       address-sized attributes.
       The     argument     comm_copy_attr_fn     may    be    specified    as
       MPI_COMM_NULL_COPY_FN or  MPI_COMM_DUP_FN  from  C,  C++,  or  Fortran.
       typedef int MPI_Comm_copy_attr_function(MPI_Comm oldcomm, int comm_keyval,
                    void *extra_state, void *attribute_val_in,
                    void *attribute_val_out, int *flag);
       and
       typedef int MPI_Comm_delete_attr_function(MPI_Comm comm, int comm_keyval,
                    void *attribute_val, void *extra_state);
       which are the same as the MPI-1.1 calls but with a new  name.  The  old
       names are deprecated.
       The Fortran callback functions are:
       SUBROUTINE COMM_COPY_ATTR_FN(OLDCOMM, COMM_KEYVAL, EXTRA_STATE,
                    ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR)
           INTEGER OLDCOMM, COMM_KEYVAL, IERROR
           INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE, ATTRIBUTE_VAL_IN,
               ATTRIBUTE_VAL_OUT
           LOGICAL FLAG
       and
       SUBROUTINE COMM_DELETE_ATTR_FN(COMM, COMM_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE,
                    IERROR)
           INTEGER COMM, COMM_KEYVAL, IERROR
           INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL, EXTRA_STATE
       The C++ callbacks are:
       typedef int MPI::Comm::Copy_attr_function(const MPI::Comm& oldcomm,
                    int comm_keyval, void* extra_state, void* attribute_val_in,
                    void* attribute_val_out, bool& flag);
       and
       typedef int MPI::Comm::Delete_attr_function(MPI::Comm& comm,
                    int comm_keyval, void* attribute_val, void* 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. C++ func-
       tions do not return errors. If the default  error  handler  is  set  to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.
       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
       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
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