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MPI_Get_count(3) man page (version 1.8.1)

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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


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

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


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