18.2.63. MPI_Comm_get_name — Open MPI 5.0.0 documentation

# 18.2.63. MPI_Comm_get_name

MPI_Comm_get_name - Returns the name that was most recently associated with a communicator.

## 18.2.63.1. SYNTAX

### 18.2.63.1.1. C Syntax

    #include <mpi.h>

    int MPI_Comm_get_name(MPI_Comm comm, char *comm_name, int *resultlen)

### 18.2.63.1.2. Fortran Syntax

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

### 18.2.63.1.3. Fortran 2008 Syntax

    USE mpi_f08
    MPI_Comm_get_name(comm, comm_name, resultlen, ierror)
         TYPE(MPI_Comm), INTENT(IN) :: comm
         CHARACTER(LEN=MPI_MAX_OBJECT_NAME), INTENT(OUT) :: comm_name
         INTEGER, INTENT(OUT) :: resultlen
         INTEGER, OPTIONAL, INTENT(OUT) :: ierror

## 18.2.63.2. INPUT PARAMETER

- `comm`: Communicator the name of which is to be returned (handle).

## 18.2.63.3. OUTPUT PARAMETER

- `comm_name`: Name previously stored on the communicator, or an empty string if no such name exists (string).

- `resultlen`: Length of returned name (integer).

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

## 18.2.63.4. DESCRIPTION

MPI_Comm_get_name returns the last name that was previously associated with the given communicator. The name may be set and retrieved from any language. The same name will be returned independent of the language used. comm_name should be allocated so that it can hold a resulting string of length MPI_MAX_OBJECT_NAME characters. MPI_Comm_get_name returns a copy of the set name in comm_name.

If the user has not associated a name with a communicator, or an error occurs, MPI_Comm_get_name will return an empty string (all spaces in Fortran, “” in C). The three predefined communicators will have predefined names associated with them. Thus, the names of MPI_COMM_WORLD, MPI_COMM_SELF, and MPI_COMM_PARENT will have the default of MPI_COMM_WORLD, MPI_COMM_SELF, and MPI_COMM_PARENT. The fact that the system may have chosen to give a default name to a communicator does not prevent the user from setting a name on the same communicator; doing this removes the old name and assigns the new one.

## 18.2.63.5. NOTES

It is safe simply to print the string returned by MPI_Comm_get_name, as it is always a valid string even if there was no name.

Note that associating a name with a communicator has no effect on the semantics of an MPI program, and will (necessarily) increase the store requirement of the program, since the names must be saved. Therefore, there is no requirement that users use these functions to associate names with communicators. However debugging and profiling MPI applications may be made easier if names are associated with communicators, since the debugger or profiler should then be able to present information in a less cryptic manner.

## 18.2.63.6. 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.