# 18.2.168. MPI_Get_address

MPI_Get_address — Gets the address of a location in memory.

## 18.2.168.1. SYNTAX

### 18.2.168.1.1. C Syntax

    #include <mpi.h>

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

### 18.2.168.1.2. 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

### 18.2.168.1.3. 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

## 18.2.168.2. INPUT PARAMETERS

- `location` : Location in caller memory (choice).

## 18.2.168.3. OUTPUT PARAMETERS

- `address` : Address of location (integer).

- `ierror` : Fortran only: Error status (integer).

## 18.2.168.4. DESCRIPTION

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

Example: Using 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.

## 18.2.168.5. 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 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 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.

## 18.2.168.6. 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.