18.2.401. MPI_Type_get_contents — Open MPI 5.0.1 documentation

# 18.2.401. MPI_Type_get_contents

MPI_Type_get_contents — Returns information about arguments used in creation of a data type.

## 18.2.401.1. SYNTAX

### 18.2.401.1.1. C Syntax

    #include <mpi.h>

    int MPI_Type_get_contents(MPI_Datatype datatype, int max_integers,
         int max_addresses, int max_datatypes, int array_of_integers[], MPI_Aint array_of_addresses[], MPI_Datatype array_of_datatypes[])

### 18.2.401.1.2. Fortran Syntax

    USE MPI
    ! or the older form: INCLUDE 'mpif.h'
    MPI_TYPE_GET_CONTENTS(DATATYPE, MAX_INTEGERS, MAX_ADDRESSES,
                 MAX_DATATYPES, ARRAY_OF_INTEGERS, ARRAY_OF_ADDRESSES,
                 ARRAY_OF_DATATYPES, IERROR)
         INTEGER DATATYPE, MAX_INTEGERS, MAX_ADDRESSES, MAX_DATATYPES
         INTEGER ARRAY_OF_INTEGERS(*), ARRAY_OF_DATATYPES(*), IERROR
         INTEGER(KIND=MPI_ADDRESS_KIND) ARRAY_OF_ADDRESSES(*)

### 18.2.401.1.3. Fortran 2008 Syntax

    USE mpi_f08
    MPI_Type_get_contents(datatype, max_integers, max_addresses, max_datatypes,
         array_of_integers, array_of_addresses, array_of_datatypes,
                 ierror)
         TYPE(MPI_Datatype), INTENT(IN) :: datatype
         INTEGER, INTENT(IN) :: max_integers, max_addresses, max_datatypes
         INTEGER, INTENT(OUT) :: array_of_integers(max_integers)
         INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(OUT) ::
         array_of_addresses(max_addresses)
         TYPE(MPI_Datatype), INTENT(OUT) :: array_of_datatypes(max_datatypes)
         INTEGER, OPTIONAL, INTENT(OUT) :: ierror

## 18.2.401.2. INPUT PARAMETERS

- `datatype`: Data type to access (handle).

- `max_integers`: Number of elements in array_of_integers (nonnegative integer).

- `max_addresses`: Number of elements in array_of_addresses (nonnegative integer).

- `max_datatypes`: Number of elements in array_of_datatypes (nonnegative integer).

## 18.2.401.3. OUTPUT PARAMETERS

- `array_of_integers`: Contains integer arguments used in constructing datatype (array of integers).

- `array_of_addresses`: Contains address arguments used in constructing datatype (array of integers).

- `array_of_datatypes`: Contains data-type arguments used in constructing datatype (array of integers).

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

## 18.2.401.4. DESCRIPTION

For the given data type, MPI_Type_get_envelope returns information on the number and type of input arguments used in the call that created the data type. The number-of-arguments values returned can be used to provide sufficiently large arrays in the decoding routine MPI_Type_get_contents. This call and the meaning of the returned values is described below. The combiner reflects the MPI data type constructor call that was used in creating datatype.

The parameter datatype must be a predefined unnamed or a derived data type. The call is erroneous if datatype is a predefined named data type.

The values given for max_integers, max_addresses, and max_datatypes must be at least as large as the value returned in num_integers, num_addresses, and num_datatypes, respectively, in the call :ref:`MPI_Type_get_envelope` for the same datatype argument.

The data types returned in array_of_datatypes are handles to data-type objects that are equivalent to the data types used in the original construction call. If these were derived data types, then the returned data types are new data-type objects, and the user is responsible for freeing these datatypes with :ref:`MPI_Type_free`. If these were predefined data types, then the returned data type is equal to that (constant) predefined data type and cannot be freed.

The committed state of returned derived data types is undefined, that is, the data types may or may not be committed. Furthermore, the content of attributes of returned data types is undefined.

Note that MPI_Type_get_contents can be invoked with a data-type argument that was constructed using MPI_Type_create_f90_real, MPI_Type_create_f90_integer, or MPI_Type_create_f90_complex (an unnamed predefined data type). In such a case, an empty array_of_datatypes is returned.

In the legacy MPI-1 datatype constructor calls, the address arguments in Fortran are of type `INTEGER`. In subsequent versions of the MPI Standard, the address arguments are of type `INTEGER(KIND=MPI_ADDRESS_KIND)`. The call MPI_Type_get_contents returns all addresses in an argument of type `INTEGER(KIND=MPI_ADDRESS_KIND)`. This is true even if the old MPI-1 calls were used. Thus, the location of values returned can be thought of as being returned by the C bindings. It can also be determined by examining the current MPI calls for datatype constructors for the deprecated MPI-1 calls that involve addresses.

## 18.2.401.5. 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.

See also

- MPI_Type_get_envelope