diff --git a/src/library.cpp b/src/library.cpp
index d815afdbb5..7840567866 100644
--- a/src/library.cpp
+++ b/src/library.cpp
@@ -137,7 +137,7 @@ void lammps_open(int argc, char **argv, MPI_Comm communicator, void **ptr)
     *ptr = (void *) lmp;
   }
   catch(LAMMPSException & e) {
-    fprintf(stderr, "LAMMPS Exception: %s", e.message.c_str());
+    fmt::print(stderr, "LAMMPS Exception: {}", e.message);
     *ptr = (void *) NULL;
   }
 #else
@@ -172,7 +172,7 @@ void lammps_open_no_mpi(int argc, char **argv, void **ptr)
     *ptr = (void *) lmp;
   }
   catch(LAMMPSException & e) {
-    fprintf(stderr, "LAMMPS Exception: %s", e.message.c_str());
+    fmt::print(stderr, "LAMMPS Exception: {}", e.message);
     *ptr = (void*) NULL;
   }
 #else
diff --git a/src/utils.cpp b/src/utils.cpp
index cac94fe0cf..b223710cab 100644
--- a/src/utils.cpp
+++ b/src/utils.cpp
@@ -155,7 +155,7 @@ void utils::sfgets(const char *srcname, int srcline, char *s, int size,
     errmsg += filename;
     errmsg += "'";
 
-    if (error) error->one(srcname,srcline,errmsg.c_str());
+    if (error) error->one(srcname,srcline,errmsg);
     if (s) *s = '\0'; // truncate string to empty in case error is NULL
   }
   return;
@@ -184,7 +184,7 @@ void utils::sfread(const char *srcname, int srcline, void *s, size_t size,
     errmsg += filename;
     errmsg += "'";
 
-    if (error) error->one(srcname,srcline,errmsg.c_str());
+    if (error) error->one(srcname,srcline,errmsg);
   }
   return;
 }
@@ -238,9 +238,9 @@ double utils::numeric(const char *file, int line, const char *str,
     msg += str;
     msg += "' in input script or data file";
     if (do_abort)
-      lmp->error->one(file,line,msg.c_str());
+      lmp->error->one(file,line,msg);
     else
-      lmp->error->all(file,line,msg.c_str());
+      lmp->error->all(file,line,msg);
   }
 
   return atof(str);
@@ -273,9 +273,9 @@ int utils::inumeric(const char *file, int line, const char *str,
     msg += str;
     msg += "' in input script or data file";
     if (do_abort)
-      lmp->error->one(file,line,msg.c_str());
+      lmp->error->one(file,line,msg);
     else
-      lmp->error->all(file,line,msg.c_str());
+      lmp->error->all(file,line,msg);
   }
 
   return atoi(str);
@@ -308,9 +308,9 @@ bigint utils::bnumeric(const char *file, int line, const char *str,
     msg += str;
     msg += "' in input script or data file";
     if (do_abort)
-      lmp->error->one(file,line,msg.c_str());
+      lmp->error->one(file,line,msg);
     else
-      lmp->error->all(file,line,msg.c_str());
+      lmp->error->all(file,line,msg);
   }
 
   return ATOBIGINT(str);
@@ -343,9 +343,9 @@ tagint utils::tnumeric(const char *file, int line, const char *str,
     msg += str;
     msg += "' in input script or data file";
     if (do_abort)
-      lmp->error->one(file,line,msg.c_str());
+      lmp->error->one(file,line,msg);
     else
-      lmp->error->all(file,line,msg.c_str());
+      lmp->error->all(file,line,msg);
   }
 
   return ATOTAGINT(str);
diff --git a/src/write_data.cpp b/src/write_data.cpp
index 677b619ada..5d67d4471c 100644
--- a/src/write_data.cpp
+++ b/src/write_data.cpp
@@ -123,7 +123,7 @@ void WriteData::command(int narg, char **arg)
     if (domain->triclinic) domain->lamda2x(atom->nlocal+atom->nghost);
   }
 
-  write(file.c_str());
+  write(file);
 }
 
 /* ----------------------------------------------------------------------
@@ -131,7 +131,7 @@ void WriteData::command(int narg, char **arg)
    might later let it be directly called within run/minimize loop
 ------------------------------------------------------------------------- */
 
-void WriteData::write(const char *file)
+void WriteData::write(const std::string &file)
 {
   // special case where reneighboring is not done in integrator
   //   on timestep data file is written (due to build_once being set)
@@ -187,7 +187,7 @@ void WriteData::write(const char *file)
   // open data file
 
   if (me == 0) {
-    fp = fopen(file,"w");
+    fp = fopen(file.c_str(),"w");
     if (fp == NULL)
       error->one(FLERR,fmt::format("Cannot open data file {}: {}",
                                    file, utils::getsyserror()));
diff --git a/src/write_data.h b/src/write_data.h
index 5055a25d98..5863b68292 100644
--- a/src/write_data.h
+++ b/src/write_data.h
@@ -21,6 +21,7 @@ CommandStyle(write_data,WriteData)
 #define LMP_WRITE_DATA_H
 
 #include "pointers.h"
+#include <string>
 
 namespace LAMMPS_NS {
 
@@ -28,7 +29,7 @@ class WriteData : protected Pointers {
  public:
   WriteData(class LAMMPS *);
   void command(int, char **);
-  void write(const char *);
+  void write(const std::string &);
 
  private:
   int me,nprocs;
diff --git a/src/write_restart.cpp b/src/write_restart.cpp
index 1469e6b3e4..3c793e5f6a 100644
--- a/src/write_restart.cpp
+++ b/src/write_restart.cpp
@@ -293,9 +293,6 @@ void WriteRestart::write(std::string file)
 
     std::string multiname = file;
     multiname.replace(multiname.find("%"),1,fmt::format("{}",icluster));
-    fp = fopen(multiname.c_str(),"wb");
-    if (fp == NULL)
-      error->one(FLERR,fmt::format("Cannot open restart file {}",multiname).c_str());
 
     if (filewriter) {
       fp = fopen(multiname.c_str(),"wb");