MPI_Get_count(3)                   Open MPI                   MPI_Get_count(3)



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


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


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_GET_COUNT(STATUS, DATATYPE, COUNT, IERROR)
            INTEGER   STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, 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
       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





1.4.1                            Jan 14, 2010                 MPI_Get_count(3)
