# Name

`MPI_Graph_get` - Retrieves graph topology information associated
with a communicator.

# Syntax

## C Syntax

```c
#include <mpi.h>

int MPI_Graph_get(MPI_Comm comm, int maxindex, int maxedges,
    int index[], int edges[])
```

## Fortran Syntax

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

MPI_GRAPH_GET(COMM, MAXINDEX, MAXEDGES, INDEX, EDGES, IERROR)
    INTEGER	COMM, MAXINDEX, MAXEDGES, INDEX(*)
    INTEGER	EDGES(*), IERROR
```

## Fortran 2008 Syntax

```fortran
USE mpi_f08

MPI_Graph_get(comm, maxindex, maxedges, index, edges, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    INTEGER, INTENT(IN) :: maxindex, maxedges
    INTEGER, INTENT(OUT) :: index(maxindex), edges(maxedges)
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

# Input Parameters

* `comm` : Communicator with graph structure (handle).
* `maxindex` : Length of vector index in the calling program (integer).
* `maxedges` : Length of vector edges in the calling program (integer).

# Output Parameters

* `index` : Array of integers containing the graph structure (for details see
the definition of `MPI_Graph_create`).
* `edges` : Array of integers containing the graph structure.
* `IERROR` : Fortran only: Error status (integer).



# Description

Functions `MPI_Graphdims_get` and `MPI_Graph_get` retrieve the
graph-topology information that was associated with a communicator by
`MPI_Graph_create`.

The information provided by `MPI_Graphdims_get` can be used to dimension
the vectors `index` and `edges` correctly for a call to `MPI_Graph_get`.

# 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.

# See Also

[`MPI_Graph_create`(3)](MPI_Graph_create.html)
[`MPI_Graphdims_get`(3)](MPI_Graphdims_get.html)