From: Daniel Arndt <arndtd@ornl.gov>
Date: Mon, 6 Jan 2020 20:55:42 +0000 (+0100)
Subject: Turn all for loops using "begin_active" into ranged-based ones
X-Git-Tag: v9.2.0-rc1~702^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=859b78470b71a71e9460bd5314357380dac47748;p=dealii.git

Turn all for loops using "begin_active" into ranged-based ones
---

diff --git a/include/deal.II/fe/fe_values.h b/include/deal.II/fe/fe_values.h
index 2b0e292ced..54ac66ad08 100644
--- a/include/deal.II/fe/fe_values.h
+++ b/include/deal.II/fe/fe_values.h
@@ -2020,9 +2020,7 @@ namespace FEValuesViews
  *
  * @code
  * FEValues values (mapping, finite_element, quadrature, flags);
- * for (cell = dof_handler.begin_active();
- *      cell != dof_handler.end();
- *      ++cell)
+ * for (const auto &cell : dof_handler.active_cell_iterators())
  *   {
  *     values.reinit(cell);
  *     for (unsigned int q=0; q<quadrature.size(); ++q)
diff --git a/include/deal.II/matrix_free/fe_evaluation.h b/include/deal.II/matrix_free/fe_evaluation.h
index c6e2604582..476904f6e8 100644
--- a/include/deal.II/matrix_free/fe_evaluation.h
+++ b/include/deal.II/matrix_free/fe_evaluation.h
@@ -1844,9 +1844,7 @@ protected:
  * @code
  * FEEvaluation<dim,fe_degree> fe_eval (mapping, finite_element,
  *                                      QGauss<1>(fe_degree+1), flags);
- * for (cell = dof_handler.begin_active();
- *      cell != dof_handler.end();
- *      ++cell)
+ * for (const auto &cell : dof_handler.active_cell_iterators())
  *   {
  *     fe_eval.reinit(cell);
  *     for (unsigned int i=0; i<dofs_per_cell;
diff --git a/include/deal.II/numerics/vector_tools.templates.h b/include/deal.II/numerics/vector_tools.templates.h
index 7c4de48eff..842ef97219 100644
--- a/include/deal.II/numerics/vector_tools.templates.h
+++ b/include/deal.II/numerics/vector_tools.templates.h
@@ -9670,14 +9670,13 @@ namespace VectorTools
                                quadrature,
                                UpdateFlags(update_JxW_values | update_values));
 
-    typename DoFHandler<dim, spacedim>::active_cell_iterator cell;
-    std::vector<Vector<Number>>                              values(
+    std::vector<Vector<Number>> values(
       quadrature.size(), Vector<Number>(dof.get_fe(0).n_components()));
 
     Number                                            mean = Number();
     typename numbers::NumberTraits<Number>::real_type area = 0.;
     // Compute mean value
-    for (cell = dof.begin_active(); cell != dof.end(); ++cell)
+    for (const auto &cell : dof.active_cell_iterators())
       if (cell->is_locally_owned())
         {
           fe.reinit(cell);
diff --git a/source/dofs/dof_tools.cc b/source/dofs/dof_tools.cc
index da3cb6402e..a266546eee 100644
--- a/source/dofs/dof_tools.cc
+++ b/source/dofs/dof_tools.cc
@@ -290,15 +290,13 @@ namespace DoFTools
 
       // then loop over all cells and do the work
       std::vector<types::global_dof_index> indices;
-      for (typename DoFHandlerType::active_cell_iterator c = dof.begin_active();
-           c != dof.end();
-           ++c)
-        if (c->is_locally_owned())
+      for (const auto &cell : dof.active_cell_iterators())
+        if (cell->is_locally_owned())
           {
-            const unsigned int fe_index      = c->active_fe_index();
-            const unsigned int dofs_per_cell = c->get_fe().dofs_per_cell;
+            const unsigned int fe_index      = cell->active_fe_index();
+            const unsigned int dofs_per_cell = cell->get_fe().dofs_per_cell;
             indices.resize(dofs_per_cell);
-            c->get_dof_indices(indices);
+            cell->get_dof_indices(indices);
             for (unsigned int i = 0; i < dofs_per_cell; ++i)
               if (dof.locally_owned_dofs().is_element(indices[i]))
                 dofs_by_block[dof.locally_owned_dofs().index_within_set(
diff --git a/source/grid/grid_generator.cc b/source/grid/grid_generator.cc
index 4285f5c816..2df876a43c 100644
--- a/source/grid/grid_generator.cc
+++ b/source/grid/grid_generator.cc
@@ -5458,9 +5458,7 @@ namespace GridGenerator
 
         // now copy the resulting level 1 cells into the new triangulation,
         cells.resize(tmp.n_active_cells(), CellData<3>());
-        for (Triangulation<3>::active_cell_iterator cell = tmp.begin_active();
-             cell != tmp.end();
-             ++cell)
+        for (const auto &cell : tmp.active_cell_iterators())
           {
             const unsigned int cell_index = cell->active_cell_index();
             for (unsigned int v = 0; v < GeometryInfo<3>::vertices_per_cell;
diff --git a/source/grid/grid_out.cc b/source/grid/grid_out.cc
index 66874f19df..51704290a3 100644
--- a/source/grid/grid_out.cc
+++ b/source/grid/grid_out.cc
@@ -820,11 +820,6 @@ GridOut::write_dx(const Triangulation<dim, spacedim> &tria,
       renumber[i] = new_number++;
   Assert(new_number == n_vertices, ExcInternalError());
 
-  typename Triangulation<dim, spacedim>::active_cell_iterator       cell;
-  const typename Triangulation<dim, spacedim>::active_cell_iterator endc =
-    tria.end();
-
-
   // write the vertices
   out << "object \"vertices\" class array type float rank 1 shape " << dim
       << " items " << n_vertices << " data follows" << '\n';
@@ -850,7 +845,7 @@ GridOut::write_dx(const Triangulation<dim, spacedim> &tria,
           << n_vertices_per_cell << " items " << n_cells << " data follows"
           << '\n';
 
-      for (cell = tria.begin_active(); cell != endc; ++cell)
+      for (const auto &cell : tria.active_cell_iterators())
         {
           for (unsigned int v = 0; v < GeometryInfo<dim>::vertices_per_cell;
                ++v)
@@ -874,13 +869,13 @@ GridOut::write_dx(const Triangulation<dim, spacedim> &tria,
 
       out << "object \"material\" class array type int rank 0 items " << n_cells
           << " data follows" << '\n';
-      for (cell = tria.begin_active(); cell != endc; ++cell)
+      for (const auto &cell : tria.active_cell_iterators())
         out << ' ' << cell->material_id();
       out << '\n' << "attribute \"dep\" string \"connections\"" << '\n' << '\n';
 
       out << "object \"level\" class array type int rank 0 items " << n_cells
           << " data follows" << '\n';
-      for (cell = tria.begin_active(); cell != endc; ++cell)
+      for (const auto &cell : tria.active_cell_iterators())
         out << ' ' << cell->level();
       out << '\n' << "attribute \"dep\" string \"connections\"" << '\n' << '\n';
 
@@ -888,7 +883,7 @@ GridOut::write_dx(const Triangulation<dim, spacedim> &tria,
         {
           out << "object \"measure\" class array type float rank 0 items "
               << n_cells << " data follows" << '\n';
-          for (cell = tria.begin_active(); cell != endc; ++cell)
+          for (const auto &cell : tria.active_cell_iterators())
             out << '\t' << cell->measure();
           out << '\n'
               << "attribute \"dep\" string \"connections\"" << '\n'
@@ -899,7 +894,7 @@ GridOut::write_dx(const Triangulation<dim, spacedim> &tria,
         {
           out << "object \"diameter\" class array type float rank 0 items "
               << n_cells << " data follows" << '\n';
-          for (cell = tria.begin_active(); cell != endc; ++cell)
+          for (const auto &cell : tria.active_cell_iterators())
             out << '\t' << cell->diameter();
           out << '\n'
               << "attribute \"dep\" string \"connections\"" << '\n'
@@ -913,7 +908,7 @@ GridOut::write_dx(const Triangulation<dim, spacedim> &tria,
           << n_vertices_per_face << " items " << n_faces << " data follows"
           << '\n';
 
-      for (cell = tria.begin_active(); cell != endc; ++cell)
+      for (const auto &cell : tria.active_cell_iterators())
         {
           for (unsigned int f = 0; f < GeometryInfo<dim>::faces_per_cell; ++f)
             {
@@ -942,7 +937,7 @@ GridOut::write_dx(const Triangulation<dim, spacedim> &tria,
 
       out << "object \"boundary\" class array type int rank 0 items " << n_faces
           << " data follows" << '\n';
-      for (cell = tria.begin_active(); cell != endc; ++cell)
+      for (const auto &cell : tria.active_cell_iterators())
         {
           // Little trick to get -1 for the interior
           for (unsigned int f = 0; f < GeometryInfo<dim>::faces_per_cell; ++f)
@@ -959,7 +954,7 @@ GridOut::write_dx(const Triangulation<dim, spacedim> &tria,
         {
           out << "object \"face measure\" class array type float rank 0 items "
               << n_faces << " data follows" << '\n';
-          for (cell = tria.begin_active(); cell != endc; ++cell)
+          for (const auto &cell : tria.active_cell_iterators())
             {
               for (unsigned int f = 0; f < GeometryInfo<dim>::faces_per_cell;
                    ++f)
@@ -973,7 +968,7 @@ GridOut::write_dx(const Triangulation<dim, spacedim> &tria,
         {
           out << "object \"face diameter\" class array type float rank 0 items "
               << n_faces << " data follows" << '\n';
-          for (cell = tria.begin_active(); cell != endc; ++cell)
+          for (const auto &cell : tria.active_cell_iterators())
             {
               for (unsigned int f = 0; f < GeometryInfo<dim>::faces_per_cell;
                    ++f)
@@ -1054,11 +1049,6 @@ GridOut::write_msh(const Triangulation<dim, spacedim> &tria,
 
   const unsigned int n_vertices = tria.n_used_vertices();
 
-  typename Triangulation<dim, spacedim>::active_cell_iterator cell =
-    tria.begin_active();
-  const typename Triangulation<dim, spacedim>::active_cell_iterator endc =
-    tria.end();
-
   // Write Header
   // The file format is:
   /*
@@ -1148,7 +1138,7 @@ GridOut::write_msh(const Triangulation<dim, spacedim> &tria,
 
   // write cells. Enumerate cells
   // consecutively, starting with 1
-  for (cell = tria.begin_active(); cell != endc; ++cell)
+  for (const auto &cell : tria.active_cell_iterators())
     {
       out << cell->active_cell_index() + 1 << ' ' << elm_type << ' '
           << static_cast<unsigned int>(cell->material_id()) << ' '
@@ -1201,11 +1191,6 @@ GridOut::write_ucd(const Triangulation<dim, spacedim> &tria,
 
   const unsigned int n_vertices = tria.n_used_vertices();
 
-  typename Triangulation<dim, spacedim>::active_cell_iterator cell =
-    tria.begin_active();
-  const typename Triangulation<dim, spacedim>::active_cell_iterator endc =
-    tria.end();
-
   // write preamble
   if (ucd_flags.write_preamble)
     {
@@ -1249,7 +1234,7 @@ GridOut::write_ucd(const Triangulation<dim, spacedim> &tria,
 
   // write cells. Enumerate cells
   // consecutively, starting with 1
-  for (cell = tria.begin_active(); cell != endc; ++cell)
+  for (const auto &cell : tria.active_cell_iterators())
     {
       out << cell->active_cell_index() + 1 << ' '
           << static_cast<unsigned int>(cell->material_id()) << ' ';
@@ -1398,10 +1383,7 @@ GridOut::write_xfig(const Triangulation<2> &tria,
   // on finer levels. Level 0
   // corresponds to a depth of 900,
   // each level subtracting 1
-  Triangulation<dim, spacedim>::cell_iterator       cell = tria.begin();
-  const Triangulation<dim, spacedim>::cell_iterator end  = tria.end();
-
-  for (; cell != end; ++cell)
+  for (const auto &cell : tria.cell_iterators())
     {
       // If depth is not encoded, write finest level only
       if (!xfig_flags.level_depth && !cell->active())
@@ -1813,9 +1795,7 @@ GridOut::write_svg(const Triangulation<2, 2> &tria, std::ostream &out) const
   y_max_perspective = projection_decomposition[1];
   y_min_perspective = projection_decomposition[1];
 
-  for (Triangulation<2, 2>::cell_iterator cell = tria.begin();
-       cell != tria.end();
-       ++cell)
+  for (const auto &cell : tria.cell_iterators())
     {
       point[0] = cell->vertex(0)[0];
       point[1] = cell->vertex(0)[1];
@@ -2124,10 +2104,7 @@ GridOut::write_svg(const Triangulation<2, 2> &tria, std::ostream &out) const
   for (unsigned int level_index = min_level; level_index <= max_level;
        level_index++)
     {
-      Triangulation<2, 2>::cell_iterator cell = tria.begin(level_index),
-                                         endc = tria.end(level_index);
-
-      for (; cell != endc; ++cell)
+      for (const auto &cell : tria.cell_iterators_on_level(level_index))
         {
           if (!svg_flags.convert_level_number_to_height && !cell->active())
             continue;
@@ -2841,12 +2818,8 @@ GridOut::write_mathgl(const Triangulation<dim, spacedim> &tria,
 
   // run over all active cells and write out a list of
   // xyz-coordinates that correspond to vertices
-  typename dealii::Triangulation<dim, spacedim>::active_cell_iterator
-    cell = tria.begin_active(),
-    endc = tria.end();
-
   // No global indices in deal.II, so we make one up here.
-  for (; cell != endc; ++cell)
+  for (const auto &cell : tria.active_cell_iterators())
     {
       for (unsigned int i = 0; i < dim; ++i)
         {
@@ -3341,8 +3314,7 @@ GridOut::write_mesh_per_processor_as_vtu(
 
   const unsigned int n_q_points = GeometryInfo<dim>::vertices_per_cell;
 
-  typename Triangulation<dim, spacedim>::cell_iterator cell, endc;
-  for (cell = tria.begin(), endc = tria.end(); cell != endc; ++cell)
+  for (const auto &cell : tria.cell_iterators())
     {
       if (!view_levels)
         {
@@ -3512,8 +3484,7 @@ GridOut::n_boundary_faces(const Triangulation<dim, spacedim> &tria) const
   typename Triangulation<dim, spacedim>::active_face_iterator face, endf;
   unsigned int                                                n_faces = 0;
 
-  for (face = tria.begin_active_face(), endf = tria.end_face(); face != endf;
-       ++face)
+  for (const auto &face : tria.active_face_iterators())
     if ((face->at_boundary()) && (face->boundary_id() != 0))
       n_faces++;
 
@@ -3537,9 +3508,7 @@ GridOut::n_boundary_lines(const Triangulation<dim, spacedim> &tria) const
 
   unsigned int n_lines = 0;
 
-  typename Triangulation<dim, spacedim>::active_cell_iterator cell, endc;
-
-  for (cell = tria.begin_active(), endc = tria.end(); cell != endc; ++cell)
+  for (const auto &cell : tria.active_cell_iterators())
     for (unsigned int l = 0; l < GeometryInfo<dim>::lines_per_cell; ++l)
       if (cell->line(l)->at_boundary() && (cell->line(l)->boundary_id() != 0) &&
           (cell->line(l)->user_flag_set() == false))
@@ -3635,10 +3604,8 @@ GridOut::write_msh_faces(const Triangulation<dim, spacedim> &tria,
                          std::ostream &                      out) const
 {
   unsigned int current_element_index = next_element_index;
-  typename Triangulation<dim, spacedim>::active_face_iterator face, endf;
 
-  for (face = tria.begin_active_face(), endf = tria.end_face(); face != endf;
-       ++face)
+  for (const auto &face : tria.active_face_iterators())
     if (face->at_boundary() && (face->boundary_id() != 0))
       {
         out << current_element_index << ' ';
@@ -3689,9 +3656,7 @@ GridOut::write_msh_lines(const Triangulation<dim, spacedim> &tria,
   const_cast<dealii::Triangulation<dim, spacedim> &>(tria)
     .clear_user_flags_line();
 
-  typename Triangulation<dim, spacedim>::active_cell_iterator cell, endc;
-
-  for (cell = tria.begin_active(), endc = tria.end(); cell != endc; ++cell)
+  for (const auto &cell : tria.active_cell_iterators())
     for (unsigned int l = 0; l < GeometryInfo<dim>::lines_per_cell; ++l)
       if (cell->line(l)->at_boundary() && (cell->line(l)->boundary_id() != 0) &&
           (cell->line(l)->user_flag_set() == false))
@@ -3802,8 +3767,7 @@ GridOut::write_ucd_faces(const Triangulation<dim, spacedim> &tria,
   unsigned int current_element_index = next_element_index;
   typename Triangulation<dim, spacedim>::active_face_iterator face, endf;
 
-  for (face = tria.begin_active_face(), endf = tria.end_face(); face != endf;
-       ++face)
+  for (const auto &face : tria.active_face_iterators())
     if (face->at_boundary() && (face->boundary_id() != 0))
       {
         out << current_element_index << "  "
@@ -3853,9 +3817,7 @@ GridOut::write_ucd_lines(const Triangulation<dim, spacedim> &tria,
   const_cast<dealii::Triangulation<dim, spacedim> &>(tria)
     .clear_user_flags_line();
 
-  typename Triangulation<dim, spacedim>::active_cell_iterator cell, endc;
-
-  for (cell = tria.begin_active(), endc = tria.end(); cell != endc; ++cell)
+  for (const auto &cell : tria.active_cell_iterators())
     for (unsigned int l = 0; l < GeometryInfo<dim>::lines_per_cell; ++l)
       if (cell->line(l)->at_boundary() && (cell->line(l)->boundary_id() != 0) &&
           (cell->line(l)->user_flag_set() == false))
@@ -3928,13 +3890,7 @@ namespace internal
     {
       AssertThrow(out, ExcIO());
 
-      const int dim = 1;
-
-      typename dealii::Triangulation<dim, spacedim>::active_cell_iterator cell =
-        tria.begin_active();
-      const typename dealii::Triangulation<dim, spacedim>::active_cell_iterator
-        endc = tria.end();
-      for (; cell != endc; ++cell)
+      for (const auto &cell : tria.active_cell_iterators())
         {
           if (gnuplot_flags.write_cell_numbers)
             out << "# cell " << cell << '\n';
@@ -3970,11 +3926,6 @@ namespace internal
         gnuplot_flags.n_boundary_face_points;
       const unsigned int n_points = 2 + n_additional_points;
 
-      typename dealii::Triangulation<dim, spacedim>::active_cell_iterator cell =
-        tria.begin_active();
-      const typename dealii::Triangulation<dim, spacedim>::active_cell_iterator
-        endc = tria.end();
-
       // If we need to plot curved lines then generate a quadrature formula to
       // place points via the mapping
       Quadrature<dim> *           q_projector = nullptr;
@@ -3994,7 +3945,7 @@ namespace internal
             QProjector<dim>::project_to_all_faces(quadrature));
         }
 
-      for (; cell != endc; ++cell)
+      for (const auto &cell : tria.active_cell_iterators())
         {
           if (gnuplot_flags.write_cell_numbers)
             out << "# cell " << cell << '\n';
@@ -4096,11 +4047,6 @@ namespace internal
         gnuplot_flags.n_boundary_face_points;
       const unsigned int n_points = 2 + n_additional_points;
 
-      typename dealii::Triangulation<dim, spacedim>::active_cell_iterator cell =
-        tria.begin_active();
-      const typename dealii::Triangulation<dim, spacedim>::active_cell_iterator
-        endc = tria.end();
-
       // If we need to plot curved lines then generate a quadrature formula to
       // place points via the mapping
       Quadrature<dim> *     q_projector = nullptr;
@@ -4122,7 +4068,7 @@ namespace internal
             QProjector<dim>::project_to_all_faces(quadrature));
         }
 
-      for (; cell != endc; ++cell)
+      for (const auto &cell : tria.active_cell_iterators())
         {
           if (gnuplot_flags.write_cell_numbers)
             out << "# cell " << cell << '\n';
@@ -4427,10 +4373,7 @@ namespace internal
 
           case 2:
             {
-              for (typename dealii::Triangulation<dim, spacedim>::
-                     active_cell_iterator cell = tria.begin_active();
-                   cell != tria.end();
-                   ++cell)
+              for (const auto &cell : tria.active_cell_iterators())
                 for (unsigned int line_no = 0;
                      line_no < GeometryInfo<dim>::lines_per_cell;
                      ++line_no)
@@ -4502,10 +4445,7 @@ namespace internal
                   // boundary faces and
                   // generate the info from
                   // them
-                  for (typename dealii::Triangulation<dim, spacedim>::
-                         active_cell_iterator cell = tria.begin_active();
-                       cell != tria.end();
-                       ++cell)
+                  for (const auto &cell : tria.active_cell_iterators())
                     for (unsigned int face_no = 0;
                          face_no < GeometryInfo<dim>::faces_per_cell;
                          ++face_no)
@@ -4558,11 +4498,6 @@ namespace internal
               // presently not supported
               Assert(mapping == nullptr, ExcNotImplemented());
 
-              typename dealii::Triangulation<dim,
-                                             spacedim>::active_cell_iterator
-                cell = tria.begin_active(),
-                endc = tria.end();
-
               // loop over all lines and compute their
               // projection on the plane perpendicular
               // to the direction of sight
@@ -4611,7 +4546,7 @@ namespace internal
               const Tensor<1, dim> unit_vector2 = vector2 / vector2.norm();
 
 
-              for (; cell != endc; ++cell)
+              for (const auto &cell : tria.active_cell_iterators())
                 for (unsigned int line_no = 0;
                      line_no < GeometryInfo<dim>::lines_per_cell;
                      ++line_no)
@@ -4777,10 +4712,7 @@ namespace internal
         {
           out << "(Helvetica) findfont 140 scalefont setfont" << '\n';
 
-          typename dealii::Triangulation<dim, spacedim>::active_cell_iterator
-            cell = tria.begin_active(),
-            endc = tria.end();
-          for (; cell != endc; ++cell)
+          for (const auto &cell : tria.active_cell_iterators())
             {
               out << (cell->center()(0) - offset(0)) * scale << ' '
                   << (cell->center()(1) - offset(1)) * scale << " m" << '\n'
@@ -4805,10 +4737,7 @@ namespace internal
           // already tracked, to avoid
           // doing this multiply
           std::set<unsigned int> treated_vertices;
-          typename dealii::Triangulation<dim, spacedim>::active_cell_iterator
-            cell = tria.begin_active(),
-            endc = tria.end();
-          for (; cell != endc; ++cell)
+          for (const auto &cell : tria.active_cell_iterators())
             for (unsigned int vertex = 0;
                  vertex < GeometryInfo<dim>::vertices_per_cell;
                  ++vertex)
diff --git a/source/grid/grid_tools.cc b/source/grid/grid_tools.cc
index f249ca7e41..90e166de58 100644
--- a/source/grid/grid_tools.cc
+++ b/source/grid/grid_tools.cc
@@ -1124,9 +1124,7 @@ namespace GridTools
       new_points.end();
 
     // fill these maps using the data given by new_points
-    typename DoFHandler<dim>::cell_iterator cell = dof_handler.begin_active(),
-                                            endc = dof_handler.end();
-    for (; cell != endc; ++cell)
+    for (const auto &cell : dof_handler.active_cell_iterators())
       {
         // loop over all vertices of the cell and see if it is listed in the map
         // given as first argument of the function
@@ -1164,7 +1162,7 @@ namespace GridTools
     // change the coordinates of the points of the triangulation
     // according to the computed values
     std::vector<bool> vertex_touched(triangulation.n_vertices(), false);
-    for (cell = dof_handler.begin_active(); cell != endc; ++cell)
+    for (const auto &cell : dof_handler.active_cell_iterators())
       for (unsigned int vertex_no = 0;
            vertex_no < GeometryInfo<dim>::vertices_per_cell;
            ++vertex_no)
@@ -4076,17 +4074,13 @@ namespace GridTools
     unsigned int iter                = 0;
     bool         continue_refinement = true;
 
-    typename Triangulation<dim, spacedim>::active_cell_iterator
-      cell = tria.begin_active(),
-      endc = tria.end();
-
     while (continue_refinement && (iter < max_iterations))
       {
         if (max_iterations != numbers::invalid_unsigned_int)
           iter++;
         continue_refinement = false;
 
-        for (cell = tria.begin_active(); cell != endc; ++cell)
+        for (const auto &cell : tria.active_cell_iterators())
           for (unsigned int j = 0; j < GeometryInfo<dim>::faces_per_cell; j++)
             if (cell->at_boundary(j) == false &&
                 cell->neighbor(j)->has_children())
@@ -4113,15 +4107,11 @@ namespace GridTools
     unsigned int iter                = 0;
     bool         continue_refinement = true;
 
-    typename Triangulation<dim, spacedim>::active_cell_iterator
-      cell = tria.begin_active(),
-      endc = tria.end();
-
     while (continue_refinement && (iter < max_iterations))
       {
         iter++;
         continue_refinement = false;
-        for (cell = tria.begin_active(); cell != endc; ++cell)
+        for (const auto &cell : tria.active_cell_iterators())
           {
             std::pair<unsigned int, double> info =
               GridTools::get_longest_direction<dim, spacedim>(cell);
diff --git a/source/grid/grid_tools_dof_handlers.cc b/source/grid/grid_tools_dof_handlers.cc
index 5da7755d20..33657df523 100644
--- a/source/grid/grid_tools_dof_handlers.cc
+++ b/source/grid/grid_tools_dof_handlers.cc
@@ -747,9 +747,7 @@ namespace GridTools
     // Find the cells for which the predicate is true
     // These are the cells around which we wish to construct
     // the halo layer
-    for (typename MeshType::active_cell_iterator cell = mesh.begin_active();
-         cell != mesh.end();
-         ++cell)
+    for (const auto &cell : mesh.active_cell_iterators())
       if (predicate(cell)) // True predicate --> Part of subdomain
         for (unsigned int v = 0;
              v < GeometryInfo<MeshType::dimension>::vertices_per_cell;
@@ -759,9 +757,7 @@ namespace GridTools
     // Find the cells that do not conform to the predicate
     // but share a vertex with the selected subdomain
     // These comprise the halo layer
-    for (typename MeshType::active_cell_iterator cell = mesh.begin_active();
-         cell != mesh.end();
-         ++cell)
+    for (const auto &cell : mesh.active_cell_iterators())
       if (!predicate(cell)) // False predicate --> Potential halo cell
         for (unsigned int v = 0;
              v < GeometryInfo<MeshType::dimension>::vertices_per_cell;
@@ -908,9 +904,7 @@ namespace GridTools
 
     // Find the cells for which the predicate is false
     // These are the cells which are around the predicate subdomain
-    for (typename MeshType::active_cell_iterator cell = mesh.begin_active();
-         cell != mesh.end();
-         ++cell)
+    for (const auto &cell : mesh.active_cell_iterators())
       if (!predicate(cell)) // Negation of predicate --> Not Part of subdomain
         {
           for (unsigned int v = 0;
@@ -930,9 +924,7 @@ namespace GridTools
 
     // Find the cells that conform to the predicate
     // but share a vertex with the cell not in the predicate subdomain
-    for (typename MeshType::active_cell_iterator cell = mesh.begin_active();
-         cell != mesh.end();
-         ++cell)
+    for (const auto &cell : mesh.active_cell_iterators())
       if (predicate(cell)) // True predicate --> Potential boundary cell of the
                            // subdomain
         for (unsigned int v = 0;
@@ -993,9 +985,7 @@ namespace GridTools
     // cells that are inside the extended bounding box but are not part of the
     // predicate subdomain are possible candidates to be within the distance to
     // the boundary cells of the predicate subdomain.
-    for (typename MeshType::active_cell_iterator cell = mesh.begin_active();
-         cell != mesh.end();
-         ++cell)
+    for (const auto &cell : mesh.active_cell_iterators())
       {
         // Ignore all the cells that are in the predicate subdomain
         if (predicate(cell))
@@ -1092,9 +1082,7 @@ namespace GridTools
     Point<MeshType::space_dimension> maxp, minp;
 
     // initialize minp and maxp with the first predicate cell center
-    for (typename MeshType::active_cell_iterator cell = mesh.begin_active();
-         cell != mesh.end();
-         ++cell)
+    for (const auto &cell : mesh.active_cell_iterators())
       if (predicate(cell))
         {
           minp = cell->center();
@@ -1104,9 +1092,7 @@ namespace GridTools
 
     // Run through all the cells to check if it belongs to predicate domain,
     // if it belongs to the predicate domain, extend the bounding box.
-    for (typename MeshType::active_cell_iterator cell = mesh.begin_active();
-         cell != mesh.end();
-         ++cell)
+    for (const auto &cell : mesh.active_cell_iterators())
       if (predicate(cell)) // True predicate --> Part of subdomain
         for (unsigned int v = 0;
              v < GeometryInfo<MeshType::dimension>::vertices_per_cell;
diff --git a/source/grid/tria.cc b/source/grid/tria.cc
index a2d8abfbc1..ef063853f4 100644
--- a/source/grid/tria.cc
+++ b/source/grid/tria.cc
@@ -10726,8 +10726,7 @@ Triangulation<dim, spacedim>::create_triangulation(
           // is disconnected that we
           // still get all cells
           if (next_round.size() == 0)
-            for (active_cell_iterator cell = begin_active(); cell != end();
-                 ++cell)
+            for (const auto &cell : this->active_cell_iterators())
               if (cell->user_flag_set() == false)
                 {
                   next_round.push_back(cell);
@@ -10753,7 +10752,7 @@ Triangulation<dim, spacedim>::flip_all_direction_flags()
 {
   AssertThrow(dim + 1 == spacedim,
               ExcMessage("Only works for dim == spacedim-1"));
-  for (active_cell_iterator cell = begin_active(); cell != end(); ++cell)
+  for (const auto &cell : this->active_cell_iterators())
     cell->set_direction_flag(!cell->direction_flag());
 }
 
diff --git a/source/hp/dof_handler.cc b/source/hp/dof_handler.cc
index 023d931555..357e2b27b6 100644
--- a/source/hp/dof_handler.cc
+++ b/source/hp/dof_handler.cc
@@ -333,10 +333,8 @@ namespace internal
                ++level)
             {
               types::global_dof_index counter = 0;
-              typename HpDoFHandler<dim, spacedim>::active_cell_iterator
-                cell = dof_handler.begin_active(level),
-                endc = dof_handler.end_active(level);
-              for (; cell != endc; ++cell)
+              for (const auto &cell :
+                   dof_handler.active_cell_iterators_on_level(level))
                 if (!cell->has_children() && !cell->is_artificial())
                   counter += cell->get_fe().template n_dofs_per_object<dim>();
 
@@ -348,7 +346,8 @@ namespace internal
               // number of active, non-artificial cells (because these are
               // exactly the cells on which we do something)
               unsigned int n_active_non_artificial_cells = 0;
-              for (cell = dof_handler.begin_active(level); cell != endc; ++cell)
+              for (const auto &cell :
+                   dof_handler.active_cell_iterators_on_level(level))
                 if (!cell->has_children() && !cell->is_artificial())
                   ++n_active_non_artificial_cells;
 
diff --git a/source/multigrid/mg_tools.cc b/source/multigrid/mg_tools.cc
index 93a77e58df..e9cd8a6e33 100644
--- a/source/multigrid/mg_tools.cc
+++ b/source/multigrid/mg_tools.cc
@@ -125,11 +125,8 @@ namespace MGTools
     user_flags_triangulation.save_user_flags(old_flags);
     user_flags_triangulation.clear_user_flags();
 
-    const typename DoFHandler<dim, spacedim>::cell_iterator end =
-      dofs.end(level);
-    typename DoFHandler<dim, spacedim>::active_cell_iterator cell;
-    std::vector<types::global_dof_index>                     cell_indices;
-    std::vector<types::global_dof_index>                     neighbor_indices;
+    std::vector<types::global_dof_index> cell_indices;
+    std::vector<types::global_dof_index> neighbor_indices;
 
     // We loop over cells and go from
     // cells to lower dimensional
@@ -138,7 +135,7 @@ namespace MGTools
     // unknown number of cells may
     // share an object of dimension
     // smaller than dim-1.
-    for (cell = dofs.begin(level); cell != end; ++cell)
+    for (const auto &cell : dofs.cell_iterators_on_level(level))
       {
         const FiniteElement<dim> &fe = cell->get_fe();
         cell_indices.resize(fe.dofs_per_cell);
@@ -310,11 +307,8 @@ namespace MGTools
     user_flags_triangulation.save_user_flags(old_flags);
     user_flags_triangulation.clear_user_flags();
 
-    const typename DoFHandler<dim, spacedim>::cell_iterator end =
-      dofs.end(level);
-    typename DoFHandler<dim, spacedim>::active_cell_iterator cell;
-    std::vector<types::global_dof_index>                     cell_indices;
-    std::vector<types::global_dof_index>                     neighbor_indices;
+    std::vector<types::global_dof_index> cell_indices;
+    std::vector<types::global_dof_index> neighbor_indices;
 
     // We have to translate the
     // couplings from components to
@@ -332,7 +326,7 @@ namespace MGTools
     // unknown number of cells may
     // share an object of dimension
     // smaller than dim-1.
-    for (cell = dofs.begin_active(); cell != end; ++cell)
+    for (const auto &cell : dofs.cell_iterators_on_level(level))
       {
         const FiniteElement<dim> &fe       = cell->get_fe();
         const unsigned int        fe_index = cell->active_fe_index();
diff --git a/source/numerics/time_dependent.cc b/source/numerics/time_dependent.cc
index ee8a1853bb..99ff0ae1c0 100644
--- a/source/numerics/time_dependent.cc
+++ b/source/numerics/time_dependent.cc
@@ -535,12 +535,10 @@ TimeStepBase_Tria<dim>::restore_grid()
 
       // limit refinement depth if the user
       // desired so
-      //       if (flags.max_refinement_level != 0)
+      //    if (flags.max_refinement_level != 0)
       //      {
       //        typename Triangulation<dim>::active_cell_iterator cell, endc;
-      //        for (cell = tria->begin_active(),
-      //             endc = tria->end();
-      //             cell!=endc; ++cell)
+      //        for (const auto &cell : tria->active_cell_iterators())
       //          if (static_cast<unsigned int>(cell->level()) >=
       //              flags.max_refinement_level)
       //            cell->clear_refine_flag();