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](#SYNTAX)

## [C Syntax](#C_Syntax)

```
#include <mpi.h>
int MPI_Add_error_class(int *errorclass)
```

## [Fortran Syntax](#Fortran_Syntax)

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


     INTEGER ERRORCLASS, IERROR
```

## [Fortran 2008 Syntax](#Fortran_2008_Syntax)

```
USE mpi_f08
MPI_Add_error_class(errorclass, ierror)


     INTEGER, INTENT(OUT) :: errorclass


     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

# [OUTPUT PARAMETERS](#OUTPUT_PARAMETERS)

- **errorclass**: New error class (integer).
- **ierror**: Fortran only: Error status (integer).

# [DESCRIPTION](#DESCRIPTION)

The function MPI\_Add\_error\_class creates a new, local error class.

# [NOTES](#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 &lt;#mpi-add-error-string&gt; 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 &lt;#mpi-add-error-string&gt; 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](#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 &lt;#mpi-init&gt;/MPI\_Init\_thread &lt;#mpi-init-thread&gt;, after MPI\_Finalize &lt;#mpi-finalize&gt;, 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 &lt;#mpi-comm-set-errhandler&gt; 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 &lt;#mpi-comm-spawn&gt;/MPI\_Comm\_spawn\_multiple &lt;#mpi-comm-spawn-multiple&gt;. 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 &lt;#mpi-abort&gt; was called on that communicator. If called on a window or file, acts as if MPI\_Abort &lt;#mpi-abort&gt; 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 &lt;#mpi-comm-create-errhandler&gt; then MPI\_Comm\_set\_errhandler &lt;#mpi-comm-set-errhandler&gt;
- MPI\_File\_create\_errhandler &lt;#mpi-file-create-errhandler&gt; then MPI\_File\_set\_errhandler &lt;#mpi-file-set-errhandler&gt;
- MPI\_Session\_create\_errhandler &lt;#mpi-session-create-errhandler&gt; then MPI\_Session\_set\_errhandler &lt;#mpi-session-set-errhandler&gt; or at MPI\_Session\_init &lt;#mpi-session-init&gt;
- MPI\_Win\_create\_errhandler &lt;#mpi-win-create-errhandler&gt; then MPI\_Win\_set\_errhandler &lt;#mpi-win-set-errhandler&gt;

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

See the MPI man page &lt;#open-mpi&gt; for a full list of MPI error codes &lt;#open-mpi-errors&gt;.

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

**See also:**

- MPI\_Add\_error\_code &lt;#mpi-add-error-code&gt;
- MPI\_Add\_error\_string &lt;#mpi-add-error-string&gt;
- MPI\_Error\_class &lt;#mpi-error-class&gt;
- MPI\_Error\_string &lt;#mpi-error-string&gt;

# [Copyright](#Copyright)

2003-2026, The Open MPI Community

September 16, 2026

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Document: MPI_Add_error_class(3) from openmpi 5.0.11-r1 (Chainguard OS)
Source: https://github.com/open-mpi/ompi