diff --git a/src/atom.cpp b/src/atom.cpp
index 8e8c1a2bb8..5d3b960731 100755
--- a/src/atom.cpp
+++ b/src/atom.cpp
@@ -1990,7 +1990,7 @@ void Atom::add_molecule_atom(Molecule *onemol, int iatom,
    allocate space for type label map
 ------------------------------------------------------------------------- */
 
-void Atom::add_label_map(char *mapID)
+void Atom::add_label_map(std::string mapID)
 {
   labelmapflag = 1;
   lmaps = (LabelMap **)
diff --git a/src/atom.h b/src/atom.h
index 94741261b0..4eb62bdfe4 100755
--- a/src/atom.h
+++ b/src/atom.h
@@ -329,7 +329,7 @@ class Atom : protected Pointers {
   int find_molecule(char *);
   void add_molecule_atom(class Molecule *, int, int, tagint);
 
-  void add_label_map(char *);
+  void add_label_map(std::string mapID = "");
   int find_label(std::string, int);
 
   void first_reorder();
diff --git a/src/input.cpp b/src/input.cpp
index 31cd037e8e..e51643fbfa 100755
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -668,7 +668,8 @@ void Input::substitute(char *&str, char *&str2, int &max, int &max2, int flag)
 void Input::readtype(char *&str, int mode)
 {
   int numflag = 1;
-  for (int i = 0; i < strlen(str); i++)
+  int n = strlen(str);
+  for (int i = 0; i < n; i++)
     if (!isdigit(str[i]) && str[i] != '*') numflag = 0;
   if (numflag) return;
   if (!atom->labelmapflag) error->all(FLERR,fmt::format("Invalid type {}",str));
@@ -1593,7 +1594,7 @@ void Input::labelmap()
 {
   if (domain->box_exist == 0)
     error->all(FLERR,"Labelmap command before simulation box is defined");
-  if (!atom->labelmapflag) atom->add_label_map("");
+  if (!atom->labelmapflag) atom->add_label_map();
   atom->lmaps[0]->modify_lmap(narg,arg);
 }
 
diff --git a/src/read_data.cpp b/src/read_data.cpp
index fd60a2b9b2..35c4ebb49b 100755
--- a/src/read_data.cpp
+++ b/src/read_data.cpp
@@ -1974,7 +1974,7 @@ void ReadData::typelabels(std::vector<std::string> &mytypelabel, int myntypes, i
   char *buf = new char[myntypes*MAXLINE];
 
   labelflag = 1;
-  if (!atom->labelmapflag) atom->add_label_map("");
+  if (!atom->labelmapflag) atom->add_label_map();
 
   int eof = comm->read_lines_from_file(fp,myntypes,MAXLINE,buf);
   if (eof) error->all(FLERR,"Unexpected end of data file");
diff --git a/src/read_restart.cpp b/src/read_restart.cpp
index d3b3f70b4a..fcfadb6d22 100644
--- a/src/read_restart.cpp
+++ b/src/read_restart.cpp
@@ -932,7 +932,7 @@ void ReadRestart::type_arrays()
 
     } else if (flag == LABELMAP) {
       read_int();
-      atom->add_label_map("");
+      atom->add_label_map();
       atom->lmaps[0]->read_restart(fp);
 
     } else error->all(FLERR,