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
- 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