MPI\_GET\_ELEMENTS(3) Open MPI MPI\_GET\_ELEMENTS(3) MPI\_Get\_elements, MPI\_Get\_elements\_x <#mpi-get-elements-x> - Returns the number of basic elements in a data type. # [SYNTAX](#SYNTAX) ## [C Syntax](#C_Syntax) ``` #include int MPI_Get_elements(const MPI_Status *status, MPI_Datatype datatype, int *count) int MPI_Get_elements_x(const MPI_Status *status, MPI_Datatype datatype, MPI_Count *count) ``` ## [Fortran Syntax](#Fortran_Syntax) ``` USE MPI ! or the older form: INCLUDE 'mpif.h' MPI_GET_ELEMENTS(STATUS, DATATYPE, COUNT, IERROR) INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR MPI_GET_ELEMENTS_X(STATUS, DATATYPE, COUNT, IERROR) INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE INTEGER(KIND=MPI_COUNT_KIND) COUNT INTEGER IERROR ``` ## [Fortran 2008 Syntax](#Fortran_2008_Syntax) ``` USE mpi_f08 MPI_Get_elements(status, datatype, count, ierror) TYPE(MPI_Status), INTENT(IN) :: status TYPE(MPI_Datatype), INTENT(IN) :: datatype INTEGER, INTENT(OUT) :: count INTEGER, OPTIONAL, INTENT(OUT) :: ierror MPI_Get_elements_x(status, datatype, count, ierror) TYPE(MPI_Status), INTENT(IN) :: status TYPE(MPI_Datatype), INTENT(IN) :: datatype INTEGER(KIND = MPI_COUNT_KIND), INTENT(OUT) :: count INTEGER, OPTIONAL, INTENT(OUT) :: ierror ``` # [INPUT PARAMETERS](#INPUT_PARAMETERS) - **status** : Return status of receive operation (status). - **datatype** : Datatype used by receive operation (handle). # [OUTPUT PARAMETERS](#OUTPUT_PARAMETERS) • **ierror** : Fortran only: Error status (integer). # [DESCRIPTION](#DESCRIPTION) MPI\_Get\_elements and MPI\_Get\_elements\_x <#mpi-get-elements-x> behave different from MPI\_Get\_count <#mpi-get-count>, which returns the number of “top-level entries” received, i.e., the number of “copies” of type datatype. MPI\_Get\_count <#mpi-get-count> may return any integer value k, where 0 =< k =< count. If MPI\_Get\_count <#mpi-get-count> returns k, then the number of basic elements received (and the value returned by MPI\_Get\_elements and MPI\_Get\_elements\_x) is n k, where n is the number of basic elements in the type map of datatype. If the number of basic elements received is not a multiple of n, that is, if the receive operation has not received an integral number of datatype “copies,” then MPI\_Get\_count <#mpi-get-count> returns the value MPI\_UNDEFINED. For both functions, if the count parameter cannot express the value to be returned (e.g., if the parameter is too small to hold the output value), it is set to MPI\_UNDEFINED. Example: Usage of MPI\_Get\_count <#mpi-get-count> and MPI\_Get\_elements: ``` call MPI_TYPE_CONTIGUOUS(2, MPI_REAL, Type2, ierr) call MPI_TYPE_COMMIT(Type2, ierr) call MPI_COMM_RANK(comm, rank, ierr) IF ( rank == 0 ) THEN CALL MPI_SEND(a, 2, MPI_REAL, 1, 0, comm, ierr) CALL MPI_SEND(a, 3, MPI_REAL, 1, 0, comm, ierr) ELSE CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr) CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=1 CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=2 CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr) CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=MPI_UNDEFINED CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=3 END IF ``` The function MPI\_Get\_elements can also be used after a probe to find the number of elements in the probed message. Note that the two functions MPI\_Get\_count <#mpi-get-count> and MPI\_Get\_elements return the same values when they are used with primitive data types. # [ERRORS](#ERRORS) Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument. Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI\_COMM\_SELF and will call the associated MPI error handler. When MPI\_COMM\_SELF is not initialized (i.e., before MPI\_Init <#mpi-init>/MPI\_Init\_thread <#mpi-init-thread>, after MPI\_Finalize <#mpi-finalize>, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI\_Comm\_set\_errhandler <#mpi-comm-set-errhandler> on MPI\_COMM\_SELF when using the World model, or the mpi\_initial\_errhandler CLI argument to mpiexec or info key to MPI\_Comm\_spawn <#mpi-comm-spawn>/MPI\_Comm\_spawn\_multiple <#mpi-comm-spawn-multiple>. If no other appropriate error handler has been set, then the MPI\_ERRORS\_RETURN error handler is called for MPI I/O functions and the MPI\_ERRORS\_ABORT error handler is called for all other MPI functions. Open MPI includes three predefined error handlers that can be used: - **MPI\_ERRORS\_ARE\_FATAL** Causes the program to abort all connected MPI processes. - **MPI\_ERRORS\_ABORT** An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI\_Abort <#mpi-abort> was called on that communicator. If called on a window or file, acts as if MPI\_Abort <#mpi-abort> was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process. - **MPI\_ERRORS\_RETURN** Returns an error code to the application. MPI applications can also implement their own error handlers by calling: - MPI\_Comm\_create\_errhandler <#mpi-comm-create-errhandler> then MPI\_Comm\_set\_errhandler <#mpi-comm-set-errhandler> - MPI\_File\_create\_errhandler <#mpi-file-create-errhandler> then MPI\_File\_set\_errhandler <#mpi-file-set-errhandler> - MPI\_Session\_create\_errhandler <#mpi-session-create-errhandler> then MPI\_Session\_set\_errhandler <#mpi-session-set-errhandler> or at MPI\_Session\_init <#mpi-session-init> - MPI\_Win\_create\_errhandler <#mpi-win-create-errhandler> then MPI\_Win\_set\_errhandler <#mpi-win-set-errhandler> Note that MPI does not guarantee that an MPI program can continue past an error. See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>. See the Error Handling section of the MPI-3.1 standard for more information. **See also:** MPI\_Get\_count <#mpi-get-count> # [Copyright](#Copyright) 2003-2026, The Open MPI Community October 9, 2026 --- Document: MPI_Get_elements(3) from openmpi-cuda-13.2 5.0.11-r1 (Chainguard OS) Source: https://github.com/open-mpi/ompi