Generates a new attribute key


#include "mpi.h"
int MPI_Keyval_create ( 
        MPI_Copy_function *copy_fn, 
        MPI_Delete_function *delete_fn, 
        int *keyval, 
        void *extra_state )

Input Parameters

Copy callback function for keyval
Delete callback function for keyval
Extra state for callback functions

Output Parameter

key value for future access (integer)


Key values are global (available for any and all communicators).

There are subtle differences between C and Fortran that require that the copy_fn be written in the same language that MPI_Keyval_create is called from. This should not be a problem for most users; only programers using both Fortran and C in the same program need to be sure that they follow this rule.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Errhandler_set; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error.

No error; MPI routine completed successfully.
This error is returned when some part of the MPICH implementation is unable to acquire memory.
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).