MPI_ADD_ERROR_CLASS(3)				     Open MPI				    MPI_ADD_ERROR_CLASS(3)

MPI_Add_error_class — Creates a new error class and returns its value

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Add_error_class(int *errorclass)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_ADD_ERROR_CLASS(ERRORCLASS, IERROR)
	       INTEGER ERRORCLASS, IERROR

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Add_error_class(errorclass, ierror)
	       INTEGER, INTENT(OUT) :: errorclass
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

OUTPUT PARAMETERS
       • errorclass: New error class (integer).

       • ierror: Fortran only: Error status (integer).

DESCRIPTION
       The function MPI_Add_error_class creates a new, local error class.

NOTES
       Because this function is local, the same value of errorclass may not be returned on all processes that make
       this  call,  even  if  they call the function concurrently. Thus, same error on different processes may not
       cause  the  same	 value	of  errorclass	to  be	returned.  To  reduce	the   potential	  for	confusion,
       MPI_Add_error_string  <#mpi-add-error-string> may be used on multiple processes to associate the same error
       string with the newly created errorclass. Even though errorclass may not be  consistent	across	processes,
       using  MPI_Add_error_string <#mpi-add-error-string> will ensure the error string associated with it will be
       the same everywhere.

       No function is provided to free error classes, as it is not expected that an application will  create  them
       in significant numbers.

       The value returned is always greater than or equal to MPI_ERR_LASTCODE.

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>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#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 <#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#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	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

       See also:

	  • MPI_Add_error_code <#mpi-add-error-code>

	  • MPI_Add_error_string <#mpi-add-error-string>

	  • MPI_Error_class <#mpi-error-class>

	  • MPI_Error_string <#mpi-error-string>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				    MPI_ADD_ERROR_CLASS(3)
