# Name

`MPI_Comm_compare` - Compares two communicators.

# Syntax

## C Syntax

```c
#include <mpi.h>

int MPI_Comm_compare(MPI_Comm comm1, MPI_Comm comm2, int *result)
```

## Fortran Syntax

```fortran
USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_COMM_COMPARE(COMM1, COMM2, RESULT, IERROR)
    INTEGER	COMM1, COMM2, RESULT, IERROR
```

## Fortran 2008 Syntax

```fortran
USE mpi_f08

MPI_Comm_compare(comm1, comm2, result, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm1, comm2
    INTEGER, INTENT(OUT) :: result
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```


# Input Parameters

* `comm1` : Comm1 (handle).
* `comm2` : Comm2 (handle).

# Output Parameters

* `result` : Result of comparison (integer).
* `IERROR` : Fortran only: Error status (integer).

# Description

`MPI_IDENT` `result`s if and only if `comm1` and `comm2` are handles for the
same object (identical groups and same contexts). `MPI_CONGRUENT` results
if the underlying groups are identical in constituents and rank order;
these communicators differ only by context. `MPI_SIMILAR` results of the
group members of both communicators are the same but the rank order
differs. `MPI_UNEQUAL` results otherwise.

# Errors

Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument.
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
`MPI_Comm_set_errhandler`; the predefined error handler `MPI_ERRORS_RETURN`
may be used to cause error values to be returned. Note that MPI does not
guarantee that an MPI program can continue past an error.