Provided by: openmpi-doc_5.0.7-1_all 
SYNTAX
C Syntax
#include <mpi.h>
int MPI_Register_datarep(const char *datarep,
MPI_Datarep_conversion_function *read_conversion_fn,
MPI_Datarep_conversion_function *write_conversion_fn,
MPI_Datarep_extent_function *dtype_file_extent_fn,
void *extra_state)
Fortran Syntax
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_REGISTER_DATAREP(DATAREP, READ_CONVERSION_FN,
WRITE_CONVERSION_FN, DTYPE_FILE_EXTENT_FN,
EXTRA_STATE, IERROR)
CHARACTER*(*) DATAREP
EXTERNAL READ_CONVERSION_FN, WRITE_CONVERSION_FN, DTYPE_FILE_EXTENT_FN
INTEGER IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
Fortran 2008 Syntax
USE mpi_f08
MPI_Register_datarep(datarep, read_conversion_fn, write_conversion_fn,
dtype_file_extent_fn, extra_state, ierror)
CHARACTER(LEN=*), INTENT(IN) :: datarep
PROCEDURE(MPI_Datarep_conversion_function) :: read_conversion_fn
PROCEDURE(MPI_Datarep_conversion_function) :: write_conversion_fn
PROCEDURE(MPI_Datarep_extent_function) :: dtype_file_extent_fn
INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: extra_state
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
INPUT PARAMETERS
• datarep: Data representation identifier (string).
• read_conversion_fn: Function invoked to convert from file representation to native representation
(function).
• write_conversion_fn: Function invoked to convert from native representation to file representation
(function).
• dtype_file_extent_fn: Function invoked to get the extent of a data type as represented in the file
(function).
• extra_state: Extra state.
OUTPUT PARAMETER
• ierror: Fortran only: Error status (integer).
DESCRIPTION
MPI_Register_datarep defines a data representation. It associates the data representation’s identifier (a
string) with the functions that convert from file representation to the native representation and vice
versa, with the function that gets the extent of a data type as represented in the file, as well as with
“extra state,” which is used for passing arguments. Once a data representation has been registered using
this routine, you may specify its identifier as an argument to MPI_File_set_view, causing subsequent
data-access operations to call the specified conversion functions.
The call associates read_conversion_fn, write_conversion_fn, and dtype_file_extent_fn with the data
representation identifier datarep. datarep can then be used as an argument to MPI_File_set_view, causing
subsequent data access operations to call the conversion functions to convert all data items accessed
between file data representation and native representation. MPI_Register_datarep is a local operation and
only registers the data representation for the calling MPI process. If datarep is already defined, an
error in the error class MPI_ERR_DUP_DATAREP is raised using the default file error handler. The length
of a data representation string is limited to the value of MPI_MAX_DATAREP_STRING. MPI_MAX_DATAREP_STRING
must have a value of at least 64. No routines are provided to delete data representations and free the
associated resources; it is not expected that an application will generate them in significant numbers.
NOTES
The Fortran version of each MPI I/O routine includes a final argument, IERROR, which is not defined in
the PARAMETERS sections. This argument is used to return the error status of the routine in the manner
typical for Fortran library routines.
The C version of each routine returns an error status as an integer return value.
Error classes are found in mpi.h (for C) and mpif.h (for Fortran).
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.
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2003-2025, The Open MPI Community
Feb 17, 2025 MPI_REGISTER_DATAREP(3)