Skip to content

Latest commit

 

History

History
107 lines (73 loc) · 2.75 KB

MPI_Get_address.3.rst

File metadata and controls

107 lines (73 loc) · 2.75 KB
Raw

MPI_Get_address

:ref:`MPI_Get_address` |mdash| Gets the address of a location in memory.

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Get_address(const void *location, MPI_Aint *address)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_GET_ADDRESS(LOCATION, ADDRESS, IERROR)
    <type> LOCATION(*)
    INTEGER(KIND=MPI_ADDRESS_KIND) ADDRESS
    INTEGER IERROR

Fortran 2008 Syntax

USE mpi_f08

MPI_Get_address(location, address, ierror)
    TYPE(*), DIMENSION(..), ASYNCHRONOUS :: location
    INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(OUT) :: address
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

  • location : Location in caller memory (choice).

OUTPUT PARAMETERS

  • address : Address of location (integer).
  • ierror : Fortran only: Error status (integer).

DESCRIPTION

:ref:`MPI_Get_address` returns the byte address of a location in memory.

Example: Using :ref:`MPI_Get_address` for an array.

REAL :: A(100,100)
INTEGER(MPI_ADDRESS_KIND) :: I1, I2, DIFF

CALL MPI_GET_ADDRESS(A(1,1), I1, IERROR)
CALL MPI_GET_ADDRESS(A(10,10), I2, IERROR)
DIFF = I2 - I1
! The value of DIFF is 909*sizeofreal; the values of I1 and I2 are
! implementation dependent.

NOTES

This routine is provided for both Fortran and C programmers and may be useful when writing portable code. In the current release, the address returned by this routine will be the same as that produced by the C & operator.

C users may be tempted to avoid using :ref:`MPI_Get_address` and rely on the availability of the address operator &. Note, however, that & cast-expression is a pointer, not an address. ANSI C does not require that the value of a pointer (or the pointer cast to int) be the absolute address of the object pointed at although this is commonly the case. Furthermore, referencing may not have a unique definition on machines with a segmented address space. The use of :ref:`MPI_Get_address` to "reference" C variables guarantees portability to such machines as well.

Current Fortran MPI codes will run unmodified and will port to any system. However, they may fail if addresses larger than 2^32 - 1 are used in the program. New codes should be written so that they use the new functions. This provides compatibility with C and avoids errors on 64-bit architectures. However, such newly written codes may need to be (slightly) rewritten to port to old Fortran 77 environments that do not support KIND declarations.

ERRORS