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
   C Syntax
	  #include <mpi.h>

	  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
	  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
	  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
       • status : Return status of receive operation (status).

       • datatype : Datatype used by receive operation (handle).

OUTPUT PARAMETERS
       • ierror : Fortran only: Error status (integer).

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
       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
       2003-2026, The Open MPI Community

						   Mar 05, 2026				       MPI_GET_ELEMENTS(3)
