CFD Online Discussion Forums - Neighbor of a boundary face

Code:

    List<List<bool> > neighbourFace;                          // a list for each face,

                                                                            // a list of bools for the other faces of the patch

                                                                            // The bool responds to whether they are neighbour faces or not

    label patchID = mesh.boundaryMesh().findPatchID("walls"); 

    const polyPatch& cPatch = mesh.boundaryMesh()[patchID];

    neighbourFace.setSize(cPatch.size());

    forAll(cPatch, faceI)                                             // faceI: the face whose neighbour faces we want

    {

        neighbourFace[faceI].setSize(cPatch.size());

        forAll(cPatch, faceJ)                                         // faceJ: possible neighbour face

        {

            neighbourFace[faceI][faceJ] = false;



            if (faceI != faceJ)                                        // if they are the same, they can't be neighbours

            {

                forAll(cPatch[faceI], pointI)                       // check all points of which faceI consists

                {



                    forAll(cPatch[faceJ], pointJ)                   // and compare them with the ones of faceJ

                    {

                        if (cPatch[faceI][pointI] == cPatch[faceJ][pointJ])

                            {

                                neighbourFace[faceI][faceJ] = true;

                            }

                    }

                }

            }

        }

    }

I have only tested that briefly but it seems to be working.
I check if there are common points but you can easily modify it to check if there are common edges only.