diff --git a/src/compute.cpp b/src/compute.cpp
index ba1d53e7c3..7200f66dc8 100644
--- a/src/compute.cpp
+++ b/src/compute.cpp
@@ -140,13 +140,10 @@ void Compute::modify_params(int narg, char **arg)
 
 void Compute::adjust_dof_fix()
 {
-  Fix **fix = modify->fix;
-  int nfix = modify->nfix;
-
   fix_dof = 0;
-  for (int i = 0; i < nfix; i++)
-    if (fix[i]->dof_flag)
-      fix_dof += fix[i]->dof(igroup);
+  for (auto &ifix : modify->get_fix_list())
+    if (ifix->dof_flag)
+      fix_dof += ifix->dof(igroup);
 }
 
 /* ----------------------------------------------------------------------
diff --git a/src/compute_centroid_stress_atom.cpp b/src/compute_centroid_stress_atom.cpp
index 5c6e522199..4ad9a4467c 100644
--- a/src/compute_centroid_stress_atom.cpp
+++ b/src/compute_centroid_stress_atom.cpp
@@ -194,10 +194,9 @@ void ComputeCentroidStressAtom::init()
       error->all(FLERR, "KSpace style does not support compute centroid/stress/atom");
 
   if (fixflag) {
-    for (int ifix = 0; ifix < modify->nfix; ifix++)
-      if (modify->fix[ifix]->virial_peratom_flag &&
-          modify->fix[ifix]->centroidstressflag == CENTROID_NOTAVAIL)
-        error->all(FLERR, "Fix style does not support compute centroid/stress/atom");
+    for (auto &ifix : modify->get_fix_list())
+      if (ifix->virial_peratom_flag && (ifix->centroidstressflag == CENTROID_NOTAVAIL))
+        error->all(FLERR, "Fix {} does not support compute centroid/stress/atom", ifix->style);
   }
 }
 
@@ -308,17 +307,15 @@ void ComputeCentroidStressAtom::compute_peratom()
   // fix styles are CENTROID_SAME, CENTROID_AVAIL or CENTROID_NOTAVAIL
 
   if (fixflag) {
-    Fix **fix = modify->fix;
-    int nfix = modify->nfix;
-    for (int ifix = 0; ifix < nfix; ifix++)
-      if (fix[ifix]->virial_peratom_flag && fix[ifix]->thermo_virial) {
-        if (modify->fix[ifix]->centroidstressflag == CENTROID_AVAIL) {
-          double **cvatom = modify->fix[ifix]->cvatom;
+    for (auto &ifix : modify->get_fix_list())
+      if (ifix->virial_peratom_flag && ifix->thermo_virial) {
+        if (ifix->centroidstressflag == CENTROID_AVAIL) {
+          double **cvatom = ifix->cvatom;
           if (cvatom)
             for (i = 0; i < nlocal; i++)
               for (j = 0; j < 9; j++) stress[i][j] += cvatom[i][j];
         } else {
-          double **vatom = modify->fix[ifix]->vatom;
+          double **vatom = ifix->vatom;
           if (vatom)
             for (i = 0; i < nlocal; i++) {
               for (j = 0; j < 6; j++) stress[i][j] += vatom[i][j];
diff --git a/src/compute_chunk_spread_atom.cpp b/src/compute_chunk_spread_atom.cpp
index 7409a6de78..0bcfa3265c 100644
--- a/src/compute_chunk_spread_atom.cpp
+++ b/src/compute_chunk_spread_atom.cpp
@@ -91,8 +91,7 @@ ComputeChunkSpreadAtom(LAMMPS *lmp, int narg, char **arg) :
     if (which[i] == ArgInfo::COMPUTE) {
       int icompute = modify->find_compute(ids[i]);
       if (icompute < 0)
-        error->all(FLERR,"Compute ID for compute chunk/spread/atom "
-                   "does not exist");
+        error->all(FLERR,"Compute ID for compute chunk/spread/atom does not exist");
 
       if (!utils::strmatch(modify->compute[icompute]->style,"/chunk$"))
         error->all(FLERR,"Compute for compute chunk/spread/atom "
@@ -100,32 +99,26 @@ ComputeChunkSpreadAtom(LAMMPS *lmp, int narg, char **arg) :
 
       if (argindex[i] == 0) {
         if (!modify->compute[icompute]->vector_flag)
-          error->all(FLERR,"Compute chunk/spread/atom compute "
-                     "does not calculate global vector");
+          error->all(FLERR,"Compute chunk/spread/atom compute does not calculate global vector");
       } else {
         if (!modify->compute[icompute]->array_flag)
-          error->all(FLERR,"Compute chunk/spread/atom compute "
-                     "does not calculate global array");
+          error->all(FLERR,"Compute chunk/spread/atom compute does not calculate global array");
         if (argindex[i] > modify->compute[icompute]->size_array_cols)
-          error->all(FLERR,"Compute chunk/spread/atom compute array "
-                     "is accessed out-of-range");
+          error->all(FLERR,"Compute chunk/spread/atom compute array is accessed out-of-range");
       }
 
     } else if (which[i] == ArgInfo::FIX) {
-      int ifix = modify->find_fix(ids[i]);
-      if (ifix < 0)
-        error->all(FLERR,"Fix ID for compute chunk/spread/atom does not exist");
+      auto ifix = modify->get_fix_by_id(ids[i]);
+      if (ifix)
+        error->all(FLERR,"Fix ID {} for compute chunk/spread/atom does not exist", ids[i]);
       if (argindex[i] == 0) {
-        if (!modify->fix[ifix]->vector_flag)
-          error->all(FLERR,"Compute chunk/spread/atom fix "
-                     "does not calculate global vector");
+        if (!ifix->vector_flag)
+          error->all(FLERR,"Compute chunk/spread/atom fix does not calculate global vector");
       } else {
-        if (!modify->fix[ifix]->array_flag)
-          error->all(FLERR,"Compute chunk/spread/atom fix "
-                     "does not calculate global array");
-        if (argindex[i] > modify->fix[ifix]->size_array_cols)
-          error->all(FLERR,"Compute chunk/spread/atom fix array "
-                     "is accessed out-of-range");
+        if (!ifix->array_flag)
+          error->all(FLERR,"Compute chunk/spread/atom fix does not calculate global array");
+        if (argindex[i] > ifix->size_array_cols)
+          error->all(FLERR,"Compute chunk/spread/atom fix array is accessed out-of-range");
       }
     }
   }
@@ -287,7 +280,7 @@ void ComputeChunkSpreadAtom::compute_peratom()
     // check if index exceeds fix output length/rows
 
     } else if (which[m] == ArgInfo::FIX) {
-      Fix *fix = modify->fix[n];
+      auto &fix = modify->get_fix_list()[n];
       if (update->ntimestep % fix->global_freq)
         error->all(FLERR,"Fix used in compute chunk/spread/atom not "
                    "computed at compatible time");
diff --git a/src/input.cpp b/src/input.cpp
index 336dfd584f..228c535e06 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -1870,7 +1870,7 @@ void Input::timestep()
   if (respaflag) update->integrate->reset_dt();
 
   if (force->pair) force->pair->reset_dt();
-  for (int i = 0; i < modify->nfix; i++) modify->fix[i]->reset_dt();
+  for (auto &ifix : modify->get_fix_list()) ifix->reset_dt();
   output->reset_dt();
 }
 
diff --git a/src/irregular.cpp b/src/irregular.cpp
index bc7dfe038d..3d4719aa02 100644
--- a/src/irregular.cpp
+++ b/src/irregular.cpp
@@ -998,18 +998,11 @@ void Irregular::destroy_data()
 
 void Irregular::init_exchange()
 {
-  int nfix = modify->nfix;
-  Fix **fix = modify->fix;
-
-  int onefix;
   int maxexchange_fix = 0;
-  for (int i = 0; i < nfix; i++) {
-    onefix = fix[i]->maxexchange;
-    maxexchange_fix = MAX(maxexchange_fix,onefix);
-  }
+  for (auto &ifix : modify->get_fix_list())
+    maxexchange_fix = MAX(maxexchange_fix, ifix->maxexchange);
 
-  int maxexchange = atom->avec->maxexchange + maxexchange_fix;
-  bufextra = maxexchange + BUFEXTRA;
+  bufextra = atom->avec->maxexchange + maxexchange_fix + BUFEXTRA;
 }
 
 /* ----------------------------------------------------------------------
diff --git a/src/library.cpp b/src/library.cpp
index af5fe36dd0..ace9905451 100644
--- a/src/library.cpp
+++ b/src/library.cpp
@@ -4756,10 +4756,8 @@ int lammps_has_id(void *handle, const char *category, const char *name) {
       if (strcmp(name,dump[i]->id) == 0) return 1;
     }
   } else if (strcmp(category,"fix") == 0) {
-    int nfix = lmp->modify->nfix;
-    Fix **fix = lmp->modify->fix;
-    for (int i=0; i < nfix; ++i) {
-      if (strcmp(name,fix[i]->id) == 0) return 1;
+    for (auto &ifix : lmp->modify->get_fix_list()) {
+      if (strcmp(name,ifix->id) == 0) return 1;
     }
   } else if (strcmp(category,"group") == 0) {
     int ngroup = lmp->group->ngroup;