---
name: "MPI_Comm_create_from_group"
section: "3"
platform: "linux"
package: "openmpi"
version: "5.0.11-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/MPI_Comm_create_from_group"
---

# MPI\_Comm\_create\_from\_group(3)

*MPI\_Comm\_create\_from\_group* — Creates a new communicator from a group and stringtag

## SYNTAX

### C Syntax

```
#include <mpi.h>
int MPI_Comm_create_from_group(MPI_Group group, const char *stringtag, MPI_Info info, MPI_Errhandler errhandler, MPI_Comm *newcomm)
```

### Fortran Syntax

```
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_CREATE_FROM_GROUP(GROUP, STRINGTAG, INFO, ERRHANDLER, NEWCOMM, IERROR)
    INTEGER GROUP, INFO, ERRHANDLER, NEWCOMM, IERROR
    CHARACTER*(*) STRINGTAG
```

### Fortran 2008 Syntax

```
USE mpi_f08
MPI_Comm_create_from_group(group, stringtag, info, errhandler, newcomm, ierror)
    TYPE(MPI_Group), INTENT(IN) :: group
    CHARACTER(LEN=*), INTENT(IN) :: stringtag
    TYPE(MPI_Info), INTENT(IN) :: info
    TYPE(MPI_Errhandler), INTENT(IN) :: errhandler
    TYPE(MPI_Comm), INTENT(OUT) :: newcomm
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

## INPUT PARAMETERS

- •

  **group** : Group (handler)

- •

  **stringtag** : Unique identifier for this operation (string)

- •

  **info** : info object (handler)

- •

  - **errhandler**

    error handler to be attached to the new intra-communicator (handle)

## OUTPUT PARAMETERS

- •

  **newcomm** : New communicator (handle).

- •

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

## DESCRIPTION

*MPI\_Comm\_create\_from\_group* is similar to *MPI\_Comm\_create\_group*, except that the set of MPI processes involved in the creation of the new intra-communicator is specified by a group argument, rather than the group associated with a pre-existing communicator. If a non-empty group is specified, then all MPI processes in that group must call the function and each of these MPI processes must provide the same arguments, including a group that contains the same members with the same ordering, and identical stringtag value. In the event that MPI\_GROUP\_EMPTY is supplied as the group argument, then the call is a local operation and MPI\_COMM\_NULL is returned as newcomm. The stringtag argument is analogous to the tag used for *MPI\_Comm\_create\_group*. If multiple threads at a given MPI process perform concurrent *MPI\_Comm\_create\_from\_group* operations, the user must distinguish these operations by providing different stringtag arguments. The stringtag shall not exceed MPI\_MAX\_STRINGTAG\_LEN characters in length. For C, this includes space for a null terminating character.

## NOTES

The errhandler argument specifies an error handler to be attached to the new intracommunicator. The info argument provides hints and assertions, possibly MPI implementation dependent, which indicate desired characteristics and guide communicator creation. MPI\_MAX\_STRINGTAG\_LEN shall have a value of at least 63.

## ERRORS

- Important

  In Open MPI, this function only works properly when the MPI job is launched via *mpirun / mpiexec*.  Using this function in other run-time environments is currently unsupported, and may result in undefined behavior (e.g., the MPI job may hang).

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\_create\_group*

## COPYRIGHT

2003-2026, The Open MPI Community