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MPI_Get_count - Gets the number of top-level elements received.
#include <mpi.h>
int MPI_Get_count(MPI_Status *status, MPI_Datatype datatype,
int *count)
INCLUDE ’mpif.h’
MPI_GET_COUNT(STATUS, DATATYPE, COUNT, IERROR)
INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR
#include <mpi.h>
int Status::Get_count(const Datatype& datatype) const
- status
- Return status of receive operation (status).
- datatype
- Datatype of each receive buffer element (handle).
- count
- Number of received elements (integer).
- IERROR
- Fortran only: Error status
(integer).
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.
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.
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.
MPI_Get_elements
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