# 17.2.75. MPI_Comm_set_name

MPI_Comm_set_name — Associates a name with a communicator.

## 17.2.75.1. SYNTAX

### 17.2.75.1.1. C Syntax

    #include <mpi.h>

    int MPI_Comm_set_name(MPI_Comm comm, const char *comm_name)

### 17.2.75.1.2. Fortran Syntax

    USE MPI
    ! or the older form: INCLUDE 'mpif.h'
    MPI_COMM_SET_NAME(COMM, COMM_NAME, IERROR)
         INTEGER COMM, IERROR
         CHARACTER*(*) COMM_NAME

### 17.2.75.1.3. Fortran 2008 Syntax

    USE mpi_f08
    MPI_Comm_set_name(comm, comm_name, ierror)
         TYPE(MPI_Comm), INTENT(IN) :: comm
         CHARACTER(LEN=*), INTENT(IN) :: comm_name
         INTEGER, OPTIONAL, INTENT(OUT) :: ierror

## 17.2.75.2. INPUT/OUTPUT PARAMETER

- `comm`: Communicator whose identifier is to be set (handle).

## 17.2.75.3. INPUT PARAMETER

- `comm_name`: Character string to be used as the identifier for the communicator (string).

## 17.2.75.4. OUTPUT PARAMETER

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

## 17.2.75.5. DESCRIPTION

MPI_Comm_set_name allows a user to associate a name string with a communicator. The character string that is passed to MPI_Comm_set_name is saved inside the MPI library (so it can be freed by the caller immediately after the call, or allocated on the stack). Leading spaces in name are significant, but trailing ones are not.

MPI_Comm_set_name is a local (noncollective) operation, which affects only the name of the communicator as seen in the process that made the MPI_Comm_set_name call. There is no requirement that the same (or any) name be assigned to a communicator in every process where it exists.

The length of the name that can be stored is limited to the value of MPI_MAX_OBJECT_NAME in Fortran and MPI_MAX_OBJECT_NAME-1 in C (to allow for the null terminator). Attempts to set names longer than this will result in truncation of the name. MPI_MAX_OBJECT_NAME must have a value of at least 64.

## 17.2.75.6. NOTES

Since MPI_Comm_set_name is provided to help debug code, it is sensible to give the same name to a communicator in all of the processes where it exists, to avoid confusion.

Regarding name length, under circumstances of store exhaustion, an attempt to set a name of any length could fail; therefore, the value of MPI_MAX_OBJECT_NAME should be viewed only as a strict upper bound on the name length, not a guarantee that setting names of less than this length will always succeed.

## 17.2.75.7. 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_Comm_get_name