# 17.2.402. MPI_Type_get_envelope

MPI_Type_get_envelope — Returns information about input arguments associated with a data type.

## 17.2.402.1. SYNTAX

### 17.2.402.1.1. C Syntax

    #include <mpi.h>

    int MPI_Type_get_envelope(MPI_Datatype datatype, int *num_integers,
         int *num_addresses, int *num_datatypes, int *combiner)

### 17.2.402.1.2. Fortran Syntax

    USE MPI
    ! or the older form: INCLUDE 'mpif.h'
    MPI_TYPE_GET_ENVELOPE(DATATYPE, NUM_INTEGERS, NUM_ADDRESSES,
                 NUM_DATATYPES, COMBINER, IERROR)
         INTEGER DATATYPE, NUM_INTEGERS, NUM_ADDRESSES
         INTEGER NUM_DATATYPES, COMBINER, IERROR

### 17.2.402.1.3. Fortran 2008 Syntax

    USE mpi_f08
    MPI_Type_get_envelope(datatype, num_integers, num_addresses, num_datatypes,
                 combiner, ierror)
         TYPE(MPI_Datatype), INTENT(IN) :: datatype
         INTEGER, INTENT(OUT) :: num_integers, num_addresses, num_datatypes,
         combiner
         INTEGER, OPTIONAL, INTENT(OUT) :: ierror

## 17.2.402.2. INPUT PARAMETER

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

## 17.2.402.3. OUTPUT PARAMETERS

- `num_integers`: Number of input integers used in the call constructing combiner (nonnegative integer).

- `num_addresses`: Number of input addresses used in the call constructing combiner (nonnegative integer).

- `num_datatypes`: Number of input data types used in the call constructing combiner (nonnegative integer).

- `combiner`: Combiner (state).

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

## 17.2.402.4. 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.

## 17.2.402.5. NOTES

These are the values that can be returned in combiner and their associated calls:

    Values                          Associated Calls

    MPI_COMBINER_NAMED              a named predefined data type
    MPI_COMBINER_DUP                MPI_Type_dup
    MPI_COMBINER_CONTIGUOUS         MPI_Type_contiguous
    MPI_COMBINER_VECTOR             MPI_Type_vector
    MPI_COMBINER_HVECTOR            MPI_Type_hvector
                                      and MPI_Type_create_hvector
    MPI_COMBINER_INDEXED            MPI_Type_indexed
    MPI_COMBINER_HINDEXED           MPI_Type_hindexed
                                      and MPI_Type_create_hindexed
    MPI_COMBINER_INDEXED_BLOCK      MPI_Type_create_indexed_block
    MPI_COMBINER_STRUCT             MPI_Type_struct
                                      and MPI_Type_create_struct
    MPI_COMBINER_SUBARRAY           MPI_Type_create_subarray
    MPI_COMBINER_DARRAY             MPI_Type_create_darray
    MPI_COMBINER_F90_REAL           MPI_Type_create_f90_real
    MPI_COMBINER_F90_COMPLEX        MPI_Type_create_f90_complex
    MPI_COMBINER_F90_INTEGER        MPI_Type_create_f90_integer
    MPI_COMBINER_RESIZED            MPI_Type_create_resized

If combiner is MPI_COMBINER_NAMED, then datatype is a named predefined data type.

The actual arguments used in the creation call for a data type can be obtained from the call MPI_Type_get_contents.

## 17.2.402.6. 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.

See also

- MPI_Type_get_contents