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(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 ex-
plained 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 perfor-
mance. A message might be received without counting the number of ele-
ments 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 pa-
rameter, 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++ func-
tions 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
4.1.2 Nov 24, 2021 MPI_Get_count(3)
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