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MPI_Get_elements_x(3) man page (version 5.0.0rc2)

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Name

C]MPI_Get_elementsR], C]MPI_Get_elements_xR] - Returns the number of basic elements in a data type.

Syntax

C Syntax



C]#include <mpi.h>int MPI_Get_elements(const MPI_Status *status, MPI_Datatype datatype, int *count)int MPI_Get_elements_x(const MPI_Status *status, MPI_Datatype datatype, MPI_Count *count)R]Fortran Syntax



C]USE MPI! or the older form: INCLUDE [aq]mpif.h[aq]MPI_GET_ELEMENTS(STATUS, DATATYPE, COUNT, IERROR) INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERRORMPI_GET_ELEMENTS_X(STATUS, DATATYPE, COUNT, IERROR) INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE INTEGER(KIND=MPI_COUNT_KIND) COUNT INTEGER IERRORR]Fortran 2008 Syntax



C]USE mpi_f08MPI_Get_elements(status, datatype, count, ierror) TYPE(MPI_Status), INTENT(IN) :: status TYPE(MPI_Datatype), INTENT(IN) :: datatype INTEGER, INTENT(OUT) :: count INTEGER, OPTIONAL, INTENT(OUT) :: ierrorMPI_Get_elements_x(status, datatype, count, ierror) TYPE(MPI_Status), INTENT(IN) :: status TYPE(MPI_Datatype), INTENT(IN) :: datatype INTEGER(KIND = MPI_COUNT_KIND), INTENT(OUT) :: count INTEGER, OPTIONAL, INTENT(OUT) :: ierrorR]Input Parameters

[bu]
C]statusR] : Return status of receive operation (status).
[bu]
C]datatypeR] : Datatype used by receive operation (handle).

Output Parameters

[bu]
C]IERRORR] : Fortran only: Error status (integer).

Description

C]MPI_Get_elementsR] and C]MPI_Get_elements_xR] behave different from C]MPI_Get_countR], which returns the number of [lq]top-level entries[rq] received, i.e., the number of [lq]copies[rq] of type C]datatypeR]. C]MPI_Get_countR] may return any integer value k, where 0 =< k =< count. If C]MPI_Get_countR] returns k, then the number of basic elements received (and the value returned by C]MPI_Get_elementsR] and C]MPI_Get_elements_xR]) is n k, where n is the number of basic elements in the type map of C]datatypeR]. If the number of basic elements received is not a multiple of n, that is, if the receive operation has not received an integral number of C]datatypeR] [lq]copies,[rq] then C]MPI_Get_countR] returns the value C]MPI_UNDEFINED.R] For both functions, if the count parameter cannot express the value to be returned (e.g., if the parameter is too small to hold the output value), it is set to C]MPI_UNDEFINEDR].

Example: Usage of C]MPI_Get_countR] and C]MPI_Get_elementR]:


C]//...MPI_TYPE_CONTIGUOUS(2, MPI_REAL, Type2, ierr)MPI_TYPE_COMMIT(Type2, ierr)// ...MPI_COMM_RANK(comm, rank, ierr)IF(rank.EQ.0) THEN CALL MPI_SEND(a, 2, MPI_REAL, 1, 0, comm, ierr) CALL MPI_SEND(a, 3, MPI_REAL, 1, 0, comm, ierr)ELSE CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr) CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=1 CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=2 CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr) CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=MPI_UNDEFINED CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=3END IFR]The function C]MPI_Get_elementsR] can also be used after a probe
to find the number of elements in the probed message. Note that the two functions C]MPI_Get_countR] and C]MPI_Get_elementsR] return the same values when they are used with primitive data types.

Errors

Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument.

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 C]MPI_Comm_set_errhandlerR]; the predefined error handler C]MPI_ERRORS_RETURNR] 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.

Fortran 77 Notes

The MPI standard prescribes portable Fortran syntax for the COUNT argument of C]MPI_Get_elements_xR] only for Fortran 90. FORTRAN 77 users may use the non-portable syntax


C]INTEGER*MPI_COUNT_KIND COUNTR]where C]MPI_COUNT_KINDR] is a constant defined in mpif.h and gives
the length of the declared integer in bytes.

See Also

C]MPI_Get_countR](3)


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