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

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 the “Use of General Datatypes in Communication” section of the MPI Standard.   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  return  result  of  the  function  and
       Fortran routines in the last argument.

       Before  the  error  value  is  returned,  the current MPI error handler associated with the communication
       object (e.g., communicator, window, file) is called.  If no communication object is associated  with  the
       MPI  call,  then  the call is considered attached to MPI_COMM_SELF and will call the associated MPI error
       handler.  When  MPI_COMM_SELF  is  not  initialized   (i.e.,   before   MPI_Init/MPI_Init_thread,   after
       MPI_Finalize,  or  when using the Sessions Model exclusively) the error raises the initial error handler.
       The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF  when  using
       the  World  model,  or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.  If no other appropriate error handler has been set, then the  MPI_ERRORS_RETURN
       error  handler  is  called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called on a communicator, it acts as if MPI_Abort was called on  that  communicator.  If  called  on  a
         window  or file, acts as if MPI_Abort was called on a communicator containing the group of processes in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

       If the value to be returned is larger than can fit into the count parameter, an MPI_ERR_TRUNCATE error is
       raised.

       SEE ALSO:
          MPI_Get_elements

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                                  MPI_GET_COUNT(3)