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.TH "MPI_GET_ELEMENTS_X" "3" "Jul 22, 2024" "" "Open MPI"
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\fI\%MPI_Get_elements\fP, \fI\%MPI_Get_elements_x\fP \- Returns the number of basic
elements in a data type.
.SH SYNTAX
.SS C Syntax
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.INDENT 3.5
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.nf
.ft C
#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)
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.SS Fortran Syntax
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.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq

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
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.SS Fortran 2008 Syntax
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.ft C
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
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.SH INPUT PARAMETERS
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.IP \(bu 2
\fBstatus\fP : Return status of receive operation (status).
.IP \(bu 2
\fBdatatype\fP : Datatype used by receive operation (handle).
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.SH OUTPUT PARAMETERS
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.IP \(bu 2
\fBierror\fP : Fortran only: Error status (integer).
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.SH DESCRIPTION
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\fI\%MPI_Get_elements\fP and \fI\%MPI_Get_elements_x\fP behave different from
\fI\%MPI_Get_count\fP, which returns the number of “top\-level entries” received,
i.e., the number of “copies” of type datatype. \fI\%MPI_Get_count\fP may return
any integer value k, where 0 =< k =< count. If \fI\%MPI_Get_count\fP returns k,
then the number of basic elements received (and the value returned by
\fI\%MPI_Get_elements\fP 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
\fI\%MPI_Get_count\fP 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.
.sp
Example: Usage of \fI\%MPI_Get_count\fP and \fI\%MPI_Get_elements\fP:
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.ft C
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
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The function \fI\%MPI_Get_elements\fP can also be used after a probe to find the
number of elements in the probed message. Note that the two functions
\fI\%MPI_Get_count\fP and \fI\%MPI_Get_elements\fP return the same values when they are
used with primitive data types.
.SH ERRORS
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
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
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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.
.sp
Open MPI includes three predefined error handlers that can be used:
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\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP 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.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
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MPI applications can also implement their own error handlers by calling:
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.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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Note that MPI does not guarantee that an MPI program can continue past
an error.
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See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
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See the Error Handling section of the MPI\-3.1 standard for
more information.
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\fBSEE ALSO:\fP
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\fI\%MPI_Get_count\fP
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.SH COPYRIGHT
2003-2024, The Open MPI Community
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