diff --git a/src/EXTRA-FIX/fix_ave_correlate_long.cpp b/src/EXTRA-FIX/fix_ave_correlate_long.cpp
index 6e4e26754f..1746c7f6f5 100644
--- a/src/EXTRA-FIX/fix_ave_correlate_long.cpp
+++ b/src/EXTRA-FIX/fix_ave_correlate_long.cpp
@@ -36,7 +36,6 @@
 
 #include <cmath>
 #include <cstring>
-#include <unistd.h>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -260,11 +259,11 @@ FixAveCorrelateLong::FixAveCorrelateLong(LAMMPS * lmp, int narg, char **arg):
             fprintf(fp," %s*%s",arg[5+i],arg[5+j]);
       fprintf(fp,"\n");
     }
-    filepos = ftell(fp);
+    filepos = platform::ftell(fp);
   }
 
-  delete [] title1;
-  delete [] title2;
+  delete[] title1;
+  delete[] title2;
 
   // allocate and initialize memory for calculated values and correlators
 
@@ -319,11 +318,11 @@ FixAveCorrelateLong::FixAveCorrelateLong(LAMMPS * lmp, int narg, char **arg):
 
 FixAveCorrelateLong::~FixAveCorrelateLong()
 {
-  delete [] which;
-  delete [] argindex;
-  delete [] value2index;
-  for (int i = 0; i < nvalues; i++) delete [] ids[i];
-  delete [] ids;
+  delete[] which;
+  delete[] argindex;
+  delete[] value2index;
+  for (int i = 0; i < nvalues; i++) delete[] ids[i];
+  delete[] ids;
 
   memory->destroy(values);
   memory->destroy(shift);
@@ -467,7 +466,7 @@ void FixAveCorrelateLong::end_of_step()
   evaluate();
 
   if (fp && me == 0) {
-    if (overwrite) fseek(fp,filepos,SEEK_SET);
+    if (overwrite) platform::fseek(fp,filepos);
     fprintf(fp,"# Timestep: " BIGINT_FORMAT "\n", ntimestep);
     for (unsigned int i=0;i<npcorr;++i) {
       fprintf(fp, "%lg ", t[i]*update->dt*nevery);
@@ -478,9 +477,9 @@ void FixAveCorrelateLong::end_of_step()
     }
     fflush(fp);
     if (overwrite) {
-      long fileend = ftell(fp);
-      if ((fileend > 0) && (ftruncate(fileno(fp),fileend)))
-        perror("Error while tuncating output");
+      bigint fileend = platform::ftell(fp);
+      if ((fileend > 0) && (platform::ftruncate(fp,fileend)))
+        error->warning(FLERR,"Error while tuncating output: {}", utils::getsyserror());
     }
   }
 
diff --git a/src/EXTRA-FIX/fix_ave_correlate_long.h b/src/EXTRA-FIX/fix_ave_correlate_long.h
index b62c6aefcb..a31ae78217 100644
--- a/src/EXTRA-FIX/fix_ave_correlate_long.h
+++ b/src/EXTRA-FIX/fix_ave_correlate_long.h
@@ -66,7 +66,7 @@ class FixAveCorrelateLong : public Fix {
   FILE *fp;
 
   int type, startstep, overwrite;
-  long filepos;
+  bigint filepos;
 
   int npair;    // number of correlation pairs to calculate
   double *values;
diff --git a/src/fix_ave_chunk.cpp b/src/fix_ave_chunk.cpp
index 1328a27376..36c9eaf6fc 100644
--- a/src/fix_ave_chunk.cpp
+++ b/src/fix_ave_chunk.cpp
@@ -29,7 +29,6 @@
 #include "variable.h"
 
 #include <cstring>
-#include <unistd.h>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -216,23 +215,23 @@ FixAveChunk::FixAveChunk(LAMMPS *lmp, int narg, char **arg) :
       iarg += 1;
     } else if (strcmp(arg[iarg],"format") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/chunk command");
-      delete [] format_user;
+      delete[] format_user;
       format_user = utils::strdup(arg[iarg+1]);
       format = format_user;
       iarg += 2;
     } else if (strcmp(arg[iarg],"title1") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/chunk command");
-      delete [] title1;
+      delete[] title1;
       title1 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title2") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/chunk command");
-      delete [] title2;
+      delete[] title2;
       title2 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title3") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/chunk command");
-      delete [] title3;
+      delete[] title3;
       title3 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else error->all(FLERR,"Illegal fix ave/chunk command");
@@ -348,18 +347,18 @@ FixAveChunk::FixAveChunk(LAMMPS *lmp, int narg, char **arg) :
     if (ferror(fp))
       error->one(FLERR,"Error writing file header");
 
-    filepos = ftell(fp);
+    filepos = platform::ftell(fp);
   }
 
-  delete [] title1;
-  delete [] title2;
-  delete [] title3;
+  delete[] title1;
+  delete[] title2;
+  delete[] title3;
 
   // if wildcard expansion occurred, free earg memory from expand_args()
   // wait to do this until after file comment lines are printed
 
   if (expand) {
-    for (int i = 0; i < nargnew; i++) delete [] earg[i];
+    for (int i = 0; i < nargnew; i++) delete[] earg[i];
     memory->sfree(earg);
   }
 
@@ -407,11 +406,11 @@ FixAveChunk::FixAveChunk(LAMMPS *lmp, int narg, char **arg) :
 
 FixAveChunk::~FixAveChunk()
 {
-  delete [] which;
-  delete [] argindex;
-  for (int i = 0; i < nvalues; i++) delete [] ids[i];
-  delete [] ids;
-  delete [] value2index;
+  delete[] which;
+  delete[] argindex;
+  for (int i = 0; i < nvalues; i++) delete[] ids[i];
+  delete[] ids;
+  delete[] value2index;
 
   if (fp && comm->me == 0) fclose(fp);
 
@@ -438,7 +437,7 @@ FixAveChunk::~FixAveChunk()
     }
   }
 
-  delete [] idchunk;
+  delete[] idchunk;
   which = nullptr;
   argindex = nullptr;
   ids = nullptr;
@@ -941,7 +940,7 @@ void FixAveChunk::end_of_step()
 
   if (fp && comm->me == 0) {
     clearerr(fp);
-    if (overwrite) fseek(fp,filepos,SEEK_SET);
+    if (overwrite) platform::fseek(fp,filepos);
     double count = 0.0;
     for (m = 0; m < nchunk; m++) count += count_total[m];
     fprintf(fp,BIGINT_FORMAT " %d %g\n",ntimestep,nchunk,count);
@@ -1027,9 +1026,9 @@ void FixAveChunk::end_of_step()
     fflush(fp);
 
     if (overwrite) {
-      long fileend = ftell(fp);
-      if ((fileend > 0) && (ftruncate(fileno(fp),fileend)))
-        perror("Error while tuncating output");
+      bigint fileend = platform::ftell(fp);
+      if ((fileend > 0) && (platform::ftruncate(fp,fileend)))
+        error->warning(FLERR,"Error while tuncating output: {}", utils::getsyserror());
     }
   }
 }
diff --git a/src/fix_ave_chunk.h b/src/fix_ave_chunk.h
index e7beed341f..69fdea0f06 100644
--- a/src/fix_ave_chunk.h
+++ b/src/fix_ave_chunk.h
@@ -61,7 +61,7 @@ class FixAveChunk : public Fix {
   class ComputeChunkAtom *cchunk;
   int lockforever;
 
-  long filepos;
+  bigint filepos;
 
   int maxvar;
   double *varatom;
diff --git a/src/fix_ave_correlate.cpp b/src/fix_ave_correlate.cpp
index 92b5ea3693..df6e33288e 100644
--- a/src/fix_ave_correlate.cpp
+++ b/src/fix_ave_correlate.cpp
@@ -30,7 +30,6 @@
 #include "variable.h"
 
 #include <cstring>
-#include <unistd.h>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -139,17 +138,17 @@ FixAveCorrelate::FixAveCorrelate(LAMMPS * lmp, int narg, char **arg):
       iarg += 1;
     } else if (strcmp(arg[iarg],"title1") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/correlate command");
-      delete [] title1;
+      delete[] title1;
       title1 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title2") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/correlate command");
-      delete [] title2;
+      delete[] title2;
       title2 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title3") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/correlate command");
-      delete [] title3;
+      delete[] title3;
       title3 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else error->all(FLERR,"Illegal fix ave/correlate command");
@@ -256,18 +255,18 @@ FixAveCorrelate::FixAveCorrelate(LAMMPS * lmp, int narg, char **arg):
     if (ferror(fp))
       error->one(FLERR,"Error writing file header");
 
-    filepos = ftell(fp);
+    filepos = platform::ftell(fp);
   }
 
-  delete [] title1;
-  delete [] title2;
-  delete [] title3;
+  delete[] title1;
+  delete[] title2;
+  delete[] title3;
 
   // if wildcard expansion occurred, free earg memory from expand_args()
   // wait to do this until after file comment lines are printed
 
   if (expand) {
-    for (int i = 0; i < nargnew; i++) delete [] earg[i];
+    for (int i = 0; i < nargnew; i++) delete[] earg[i];
     memory->sfree(earg);
   }
 
@@ -312,11 +311,11 @@ FixAveCorrelate::FixAveCorrelate(LAMMPS * lmp, int narg, char **arg):
 
 FixAveCorrelate::~FixAveCorrelate()
 {
-  delete [] which;
-  delete [] argindex;
-  delete [] value2index;
-  for (int i = 0; i < nvalues; i++) delete [] ids[i];
-  delete [] ids;
+  delete[] which;
+  delete[] argindex;
+  delete[] value2index;
+  for (int i = 0; i < nvalues; i++) delete[] ids[i];
+  delete[] ids;
 
   memory->destroy(values);
   memory->destroy(count);
@@ -489,7 +488,7 @@ void FixAveCorrelate::end_of_step()
 
   if (fp && me == 0) {
     clearerr(fp);
-    if (overwrite) fseek(fp,filepos,SEEK_SET);
+    if (overwrite) platform::fseek(fp,filepos);
     fprintf(fp,BIGINT_FORMAT " %d\n",ntimestep,nrepeat);
     for (i = 0; i < nrepeat; i++) {
       fprintf(fp,"%d %d %d",i+1,i*nevery,count[i]);
@@ -507,9 +506,9 @@ void FixAveCorrelate::end_of_step()
     fflush(fp);
 
     if (overwrite) {
-      long fileend = ftell(fp);
-      if ((fileend > 0) && (ftruncate(fileno(fp),fileend)))
-        perror("Error while tuncating output");
+      bigint fileend = platform::ftell(fp);
+      if ((fileend > 0) && (platform::ftruncate(fp,fileend)))
+        error->warning(FLERR,"Error while tuncating output: {}", utils::getsyserror());
     }
   }
 
diff --git a/src/fix_ave_correlate.h b/src/fix_ave_correlate.h
index d551ba7b92..6dde75c0d3 100644
--- a/src/fix_ave_correlate.h
+++ b/src/fix_ave_correlate.h
@@ -44,7 +44,7 @@ class FixAveCorrelate : public Fix {
 
   int type, ave, startstep, overwrite;
   double prefactor;
-  long filepos;
+  bigint filepos;
 
   int firstindex;    // index in values ring of earliest time sample
   int lastindex;     // index in values ring of latest time sample
diff --git a/src/fix_ave_histo.cpp b/src/fix_ave_histo.cpp
index 92b03035b3..8c55337074 100644
--- a/src/fix_ave_histo.cpp
+++ b/src/fix_ave_histo.cpp
@@ -25,7 +25,6 @@
 #include "variable.h"
 
 #include <cstring>
-#include <unistd.h>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -168,7 +167,7 @@ FixAveHisto::FixAveHisto(LAMMPS *lmp, int narg, char **arg) :
   // if wildcard expansion occurred, free earg memory from expand_args()
 
   if (expand) {
-    for (int i = 0; i < nvalues; i++) delete [] earg[i];
+    for (int i = 0; i < nvalues; i++) delete[] earg[i];
     memory->sfree(earg);
   }
 
@@ -434,12 +433,12 @@ FixAveHisto::FixAveHisto(LAMMPS *lmp, int narg, char **arg) :
     if (ferror(fp))
       error->one(FLERR,"Error writing file header");
 
-    filepos = ftell(fp);
+    filepos = platform::ftell(fp);
   }
 
-  delete [] title1;
-  delete [] title2;
-  delete [] title3;
+  delete[] title1;
+  delete[] title2;
+  delete[] title3;
 
   // allocate and initialize memory for averaging
 
@@ -502,18 +501,18 @@ FixAveHisto::FixAveHisto(LAMMPS *lmp, int narg, char **arg) :
 
 FixAveHisto::~FixAveHisto()
 {
-  delete [] which;
-  delete [] argindex;
-  delete [] value2index;
-  for (int i = 0; i < nvalues; i++) delete [] ids[i];
-  delete [] ids;
+  delete[] which;
+  delete[] argindex;
+  delete[] value2index;
+  for (int i = 0; i < nvalues; i++) delete[] ids[i];
+  delete[] ids;
 
   if (fp && me == 0) fclose(fp);
 
-  delete [] bin;
-  delete [] bin_total;
-  delete [] bin_all;
-  delete [] coord;
+  delete[] bin;
+  delete[] bin_total;
+  delete[] bin_all;
+  delete[] coord;
   memory->destroy(stats_list);
   memory->destroy(bin_list);
   memory->destroy(vector);
@@ -817,7 +816,7 @@ void FixAveHisto::end_of_step()
 
   if (fp && me == 0) {
     clearerr(fp);
-    if (overwrite) fseek(fp,filepos,SEEK_SET);
+    if (overwrite) platform::fseek(fp,filepos);
     fprintf(fp,BIGINT_FORMAT " %d %g %g %g %g\n",ntimestep,nbins,
             stats_total[0],stats_total[1],stats_total[2],stats_total[3]);
     if (stats_total[0] != 0.0)
@@ -833,9 +832,9 @@ void FixAveHisto::end_of_step()
 
     fflush(fp);
     if (overwrite) {
-      long fileend = ftell(fp);
-      if ((fileend > 0) && (ftruncate(fileno(fp),fileend)))
-        perror("Error while tuncating output");
+      bigint fileend = platform::ftell(fp);
+      if ((fileend > 0) && (platform::ftruncate(fp,fileend)))
+        error->warning(FLERR,"Error while tuncating output: {}",utils::getsyserror());
     }
   }
 }
@@ -993,17 +992,17 @@ void FixAveHisto::options(int iarg, int narg, char **arg)
       iarg += 1;
     } else if (strcmp(arg[iarg],"title1") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/histo command");
-      delete [] title1;
+      delete[] title1;
       title1 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title2") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/histo command");
-      delete [] title2;
+      delete[] title2;
       title2 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title3") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/histo command");
-      delete [] title3;
+      delete[] title3;
       title3 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else error->all(FLERR,"Illegal fix ave/histo command");
diff --git a/src/fix_ave_histo.h b/src/fix_ave_histo.h
index 0158d04377..ef64ad74ff 100644
--- a/src/fix_ave_histo.h
+++ b/src/fix_ave_histo.h
@@ -44,7 +44,7 @@ class FixAveHisto : public Fix {
   FILE *fp;
   double lo, hi, binsize, bininv;
   int kind, beyond, overwrite;
-  long filepos;
+  bigint filepos;
 
   double stats[4], stats_total[4], stats_all[4];
   double **stats_list;
diff --git a/src/fix_ave_histo_weight.cpp b/src/fix_ave_histo_weight.cpp
index 63321bf53e..7866490840 100644
--- a/src/fix_ave_histo_weight.cpp
+++ b/src/fix_ave_histo_weight.cpp
@@ -28,8 +28,6 @@
 #include "update.h"
 #include "variable.h"
 
-#include <unistd.h>
-
 using namespace LAMMPS_NS;
 using namespace FixConst;
 
@@ -472,7 +470,7 @@ void FixAveHistoWeight::end_of_step()
 
   if (fp && me == 0) {
     clearerr(fp);
-    if (overwrite) fseek(fp,filepos,SEEK_SET);
+    if (overwrite) platform::fseek(fp,filepos);
     fprintf(fp,BIGINT_FORMAT " %d %g %g %g %g\n",ntimestep,nbins,
             stats_total[0],stats_total[1],stats_total[2],stats_total[3]);
     if (stats_total[0] != 0.0)
@@ -488,9 +486,9 @@ void FixAveHistoWeight::end_of_step()
 
     fflush(fp);
     if (overwrite) {
-      long fileend = ftell(fp);
-      if ((fileend > 0) && (ftruncate(fileno(fp),fileend)))
-        perror("Error while tuncating output");
+      bigint fileend = platform::ftell(fp);
+      if ((fileend > 0) && (platform::ftruncate(fp,fileend)))
+        error->warning(FLERR,"Error while tuncating output: {}", utils::getsyserror());
     }
   }
 }
diff --git a/src/fix_ave_time.cpp b/src/fix_ave_time.cpp
index da9cd89e5e..a3da6e6a3d 100644
--- a/src/fix_ave_time.cpp
+++ b/src/fix_ave_time.cpp
@@ -28,7 +28,6 @@
 #include "variable.h"
 
 #include <cstring>
-#include <unistd.h>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
@@ -274,18 +273,18 @@ FixAveTime::FixAveTime(LAMMPS *lmp, int narg, char **arg) :
     if (ferror(fp))
       error->one(FLERR,"Error writing file header");
 
-    filepos = ftell(fp);
+    filepos = platform::ftell(fp);
   }
 
-  delete [] title1;
-  delete [] title2;
-  delete [] title3;
+  delete[] title1;
+  delete[] title2;
+  delete[] title3;
 
   // if wildcard expansion occurred, free earg memory from expand_args()
   // wait to do this until after file comment lines are printed
 
   if (expand) {
-    for (int i = 0; i < nvalues; i++) delete [] earg[i];
+    for (int i = 0; i < nvalues; i++) delete[] earg[i];
     memory->sfree(earg);
   }
 
@@ -446,24 +445,24 @@ FixAveTime::~FixAveTime()
       }
   }
 
-  delete [] format_user;
+  delete[] format_user;
 
-  delete [] which;
-  delete [] argindex;
-  delete [] value2index;
-  delete [] offcol;
-  delete [] varlen;
-  for (int i = 0; i < nvalues; i++) delete [] ids[i];
-  delete [] ids;
+  delete[] which;
+  delete[] argindex;
+  delete[] value2index;
+  delete[] offcol;
+  delete[] varlen;
+  for (int i = 0; i < nvalues; i++) delete[] ids[i];
+  delete[] ids;
 
-  delete [] extlist;
+  delete[] extlist;
 
   if (fp && me == 0) fclose(fp);
 
   memory->destroy(column);
 
-  delete [] vector;
-  delete [] vector_total;
+  delete[] vector;
+  delete[] vector_total;
   memory->destroy(array);
   memory->destroy(array_total);
   memory->destroy(array_list);
@@ -673,7 +672,7 @@ void FixAveTime::invoke_scalar(bigint ntimestep)
 
   if (fp && me == 0) {
     clearerr(fp);
-    if (overwrite) fseek(fp,filepos,SEEK_SET);
+    if (overwrite) platform::fseek(fp,filepos);
     fprintf(fp,BIGINT_FORMAT,ntimestep);
     for (i = 0; i < nvalues; i++) fprintf(fp,format,vector_total[i]/norm);
     fprintf(fp,"\n");
@@ -683,9 +682,9 @@ void FixAveTime::invoke_scalar(bigint ntimestep)
     fflush(fp);
 
     if (overwrite) {
-      long fileend = ftell(fp);
-      if ((fileend > 0) && (ftruncate(fileno(fp),fileend)))
-        perror("Error while tuncating output");
+      bigint fileend = platform::ftell(fp);
+      if ((fileend > 0) && (platform::ftruncate(fp,fileend)))
+        error->warning(FLERR,"Error while tuncating output: {}", utils::getsyserror());
     }
   }
 }
@@ -885,7 +884,7 @@ void FixAveTime::invoke_vector(bigint ntimestep)
   // output result to file
 
   if (fp && me == 0) {
-    if (overwrite) fseek(fp,filepos,SEEK_SET);
+    if (overwrite) platform::fseek(fp,filepos);
     fprintf(fp,BIGINT_FORMAT " %d\n",ntimestep,nrows);
     for (i = 0; i < nrows; i++) {
       fprintf(fp,"%d",i+1);
@@ -894,9 +893,9 @@ void FixAveTime::invoke_vector(bigint ntimestep)
     }
     fflush(fp);
     if (overwrite) {
-      long fileend = ftell(fp);
-      if ((fileend > 0) && (ftruncate(fileno(fp),fileend)))
-        perror("Error while tuncating output");
+      bigint fileend = platform::ftell(fp);
+      if ((fileend > 0) && (platform::ftruncate(fp,fileend)))
+        error->warning(FLERR,"Error while tuncating output: {}", utils::getsyserror());
     }
   }
 }
@@ -1066,23 +1065,23 @@ void FixAveTime::options(int iarg, int narg, char **arg)
       iarg += 1;
     } else if (strcmp(arg[iarg],"format") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/time command");
-      delete [] format_user;
+      delete[] format_user;
       format_user = utils::strdup(arg[iarg+1]);
       format = format_user;
       iarg += 2;
     } else if (strcmp(arg[iarg],"title1") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/spatial command");
-      delete [] title1;
+      delete[] title1;
       title1 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title2") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/spatial command");
-      delete [] title2;
+      delete[] title2;
       title2 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"title3") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal fix ave/spatial command");
-      delete [] title3;
+      delete[] title3;
       title3 = utils::strdup(arg[iarg+1]);
       iarg += 2;
     } else error->all(FLERR,"Illegal fix ave/time command");
diff --git a/src/fix_ave_time.h b/src/fix_ave_time.h
index 391a06f495..3a26dd6d70 100644
--- a/src/fix_ave_time.h
+++ b/src/fix_ave_time.h
@@ -54,7 +54,7 @@ class FixAveTime : public Fix {
   int *offlist;
   char *format, *format_user;
   char *title1, *title2, *title3;
-  long filepos;
+  bigint filepos;
 
   int norm, iwindow, window_limit;
   double *vector;