oracular (3) MPI_Get_count.openmpi.3.gz

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NAME
       MPI_Get_count  - Gets the number of top-level elements received.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Get_count(const MPI_Status *status, MPI_Datatype datatype,
            int *count)


Fortran Syntax
       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_GET_COUNT(STATUS, DATATYPE, COUNT, IERROR)
            INTEGER   STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR


Fortran 2008 Syntax
       USE mpi_f08
       MPI_Get_count(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


C++ Syntax
       #include <mpi.h>
       int Status::Get_count(const Datatype& datatype) const


INPUT PARAMETERS
       status    Return status of receive operation (status).

       datatype  Datatype of each receive buffer element (handle).


OUTPUT PARAMETERS
       count     Number of received elements (integer).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       Returns  the  number  of  entries  received.  (We  count  entries, each of type datatype, not bytes.) The
       datatype argument should match the argument provided by the receive call that set  the  status  variable.
       (As  explained  in  Section  3.12.5  in  the MPI-1 Standard, "Use of General Datatypes in Communication,"
       MPI_Get_count may, in certain situations, return the value MPI_UNDEFINED.)

       The datatype argument is passed to MPI_Get_count to improve performance.  A  message  might  be  received
       without  counting the number of elements it contains, and the count value is often not needed. Also, this
       allows the same function to be used after a call to MPI_Probe.


NOTES
       If the size of the datatype is zero, this routine will return a count of zero.  If the amount of data  in
       status is not an exact multiple of the size of datatype (so that count would not be integral), a count of
       MPI_UNDEFINED is returned instead.


ERRORS
       If the value to be returned is larger  than  can  fit  into  the  count  parameter,  an  MPI_ERR_TRUNCATE
       exception is invoked.

       Almost  all  MPI  routines  return  an  error  value; C routines as the value of the function and Fortran
       routines in the last argument. C++ functions 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 not guarantee that an MPI program can continue past an error.


SEE ALSO
       MPI_Get_elements