# 17.2.407. MPI_Type_get_true_extent

MPI_Type_get_true_extent, MPI_Type_get_true_extent_x - Returns the true lower bound and extent of a data type’s corresponding typemap, ignoring MPI_UB and MPI_LB markers.

## 17.2.407.1. SYNTAX

### 17.2.407.1.1. C Syntax

    #include <mpi.h>

    int MPI_Type_get_true_extent(MPI_Datatype datatype,
         MPI_Aint *true_lb, MPI_Aint *true_extent)
    int MPI_Type_get_true_extent_x(MPI_Datatype datatype,
         MPI_Count *true_lb, MPI_Count *true_extent)

### 17.2.407.1.2. Fortran Syntax

    USE MPI
    ! or the older form: INCLUDE 'mpif.h'
    MPI_TYPE_GET_TRUE_EXTENT(DATATYPE, TRUE_LB, TRUE_EXTENT, IERROR)
         INTEGER DATATYPE, IERROR
         INTEGER(KIND=MPI_ADDRESS_KIND) TRUE_LB, TRUE_EXTENT
    MPI_TYPE_GET_TRUE_EXTENT_X(DATATYPE, TRUE_LB, TRUE_EXTENT, IERROR)
         INTEGER DATATYPE, IERROR
         INTEGER(KIND=MPI_COUNT_KIND) TRUE_LB, TRUE_EXTENT

### 17.2.407.1.3. Fortran 2008 Syntax

    USE mpi_f08
    MPI_Type_get_true_extent(datatype, true_lb, true_extent, ierror)
         TYPE(MPI_Datatype), INTENT(IN) :: datatype
         INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(OUT) :: true_lb, true_extent
         INTEGER, OPTIONAL, INTENT(OUT) :: ierror
    MPI_Type_get_true_extent_x(datatype, true_lb, true_extent, ierror)
         TYPE(MPI_Datatype), INTENT(IN) :: datatype
         INTEGER(KIND = MPI_COUNT_KIND), INTENT(OUT) :: true_lb, true_extent
         INTEGER, OPTIONAL, INTENT(OUT) :: ierror

## 17.2.407.2. INPUT PARAMETER

- `datatype`: Data type for which information is wanted (handle).

## 17.2.407.3. OUTPUT PARAMETERS

- `true_lb`: True lower bound of data type (integer).

- `true_extent`: True size of data type (integer).

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

## 17.2.407.4. DESCRIPTION

The true_lb parameter returns the offset of the lowest unit of store that is addressed by the data type, that is, the lower bound of the corresponding typemap, ignoring MPI_LB markers. The true_extent parameter returns the true size of the data type, that is, the extent of the corresponding typemap, ignoring MPI_LB and MPI_UB markers, and performing no rounding for alignment. For both functions, if either the true_lb or true_extent 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 MPI_UNDEFINED.

The true_extent is the minimum number of bytes of memory necessary to hold a data type, uncompressed.

See section 4.1.8 of the MPI-3 standard for more detailed definitions of these parameters in relation to the typemap.

## 17.2.407.5. 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.