--- a/libinterp/corefcn/gtk-manager.cc	Sun Sep 05 14:20:54 2021 -0700
+++ b/libinterp/corefcn/gtk-manager.cc	Sun Sep 05 17:26:33 2021 -0700
@@ -40,27 +40,27 @@
   {
     graphics_toolkit retval;
 
-    if (dtk.empty ())
+    if (m_dtk.empty ())
       error ("no graphics toolkits are available!");
 
-    auto pl = loaded_toolkits.find (dtk);
+    auto pl = m_loaded_toolkits.find (m_dtk);
 
-    if (pl == loaded_toolkits.end ())
+    if (pl == m_loaded_toolkits.end ())
       {
-        auto pa = available_toolkits.find (dtk);
+        auto pa = m_available_toolkits.find (m_dtk);
 
-        if (pa == available_toolkits.end ())
+        if (pa == m_available_toolkits.end ())
           error ("default graphics toolkit '%s' is not available!",
-                 dtk.c_str ());
+                 m_dtk.c_str ());
 
         octave_value_list args;
-        args(0) = dtk;
+        args(0) = m_dtk;
         feval ("graphics_toolkit", args);
 
-        pl = loaded_toolkits.find (dtk);
+        pl = m_loaded_toolkits.find (m_dtk);
 
-        if (pl == loaded_toolkits.end ())
-          error ("failed to load %s graphics toolkit", dtk.c_str ());
+        if (pl == m_loaded_toolkits.end ())
+          error ("failed to load %s graphics toolkit", m_dtk.c_str ());
 
         retval = pl->second;
       }
@@ -73,38 +73,38 @@
   void
   gtk_manager::register_toolkit (const std::string& name)
   {
-    if (dtk.empty () || name == "qt"
+    if (m_dtk.empty () || name == "qt"
         || (name == "fltk"
-            && available_toolkits.find ("qt") == available_toolkits.end ()))
-      dtk = name;
+            && m_available_toolkits.find ("qt") == m_available_toolkits.end ()))
+      m_dtk = name;
 
-    available_toolkits.insert (name);
+    m_available_toolkits.insert (name);
   }
 
   void
   gtk_manager::unregister_toolkit (const std::string& name)
   {
-    available_toolkits.erase (name);
+    m_available_toolkits.erase (name);
 
-    if (dtk == name)
+    if (m_dtk == name)
       {
-        if (available_toolkits.empty ())
-          dtk.clear ();
+        if (m_available_toolkits.empty ())
+          m_dtk.clear ();
         else
           {
-            auto pa = available_toolkits.cbegin ();
+            auto pa = m_available_toolkits.cbegin ();
 
-            dtk = *pa++;
+            m_dtk = *pa++;
 
-            while (pa != available_toolkits.cend ())
+            while (pa != m_available_toolkits.cend ())
               {
                 std::string tk_name = *pa++;
 
                 if (tk_name == "qt"
                     || (tk_name == "fltk"
-                        && (available_toolkits.find ("qt")
-                            == available_toolkits.cend ())))
-                  dtk = tk_name;
+                        && (m_available_toolkits.find ("qt")
+                            == m_available_toolkits.cend ())))
+                  m_dtk = tk_name;
               }
           }
       }

--- a/libinterp/corefcn/gtk-manager.h	Sun Sep 05 14:20:54 2021 -0700
+++ b/libinterp/corefcn/gtk-manager.h	Sun Sep 05 17:26:33 2021 -0700
@@ -56,19 +56,19 @@
 
     void load_toolkit (const graphics_toolkit& tk)
     {
-      loaded_toolkits[tk.get_name ()] = tk;
+      m_loaded_toolkits[tk.get_name ()] = tk;
     }
 
     void unload_toolkit (const std::string& name)
     {
-      loaded_toolkits.erase (name);
+      m_loaded_toolkits.erase (name);
     }
 
     graphics_toolkit find_toolkit (const std::string& name) const
     {
-      auto p = loaded_toolkits.find (name);
+      auto p = m_loaded_toolkits.find (name);
 
-      if (p != loaded_toolkits.end ())
+      if (p != m_loaded_toolkits.end ())
         return p->second;
       else
         return graphics_toolkit ();
@@ -76,10 +76,10 @@
 
     Cell available_toolkits_list (void) const
     {
-      Cell m (1, available_toolkits.size ());
+      Cell m (1, m_available_toolkits.size ());
 
       octave_idx_type i = 0;
-      for (const auto& tkit : available_toolkits)
+      for (const auto& tkit : m_available_toolkits)
         m(i++) = tkit;
 
       return m;
@@ -87,10 +87,10 @@
 
     Cell loaded_toolkits_list (void) const
     {
-      Cell m (1, loaded_toolkits.size ());
+      Cell m (1, m_loaded_toolkits.size ());
 
       octave_idx_type i = 0;
-      for (const auto& nm_tkit_p : loaded_toolkits)
+      for (const auto& nm_tkit_p : m_loaded_toolkits)
         m(i++) = nm_tkit_p.first;
 
       return m;
@@ -98,32 +98,32 @@
 
     void unload_all_toolkits (void)
     {
-      while (! loaded_toolkits.empty ())
+      while (! m_loaded_toolkits.empty ())
         {
-          auto p = loaded_toolkits.begin ();
+          auto p = m_loaded_toolkits.begin ();
 
           std::string name = p->first;
 
           p->second.close ();
 
           // The toolkit may have unloaded itself.  If not, we'll do it here.
-          if (loaded_toolkits.find (name) != loaded_toolkits.end ())
+          if (m_loaded_toolkits.find (name) != m_loaded_toolkits.end ())
             unload_toolkit (name);
         }
     }
 
-    std::string default_toolkit (void) const { return dtk; }
+    std::string default_toolkit (void) const { return m_dtk; }
 
   private:
 
     // The name of the default toolkit.
-    std::string dtk;
+    std::string m_dtk;
 
     // The list of toolkits that we know about.
-    std::set<std::string> available_toolkits;
+    std::set<std::string> m_available_toolkits;
 
     // The list of toolkits we have actually loaded.
-    std::map<std::string, graphics_toolkit> loaded_toolkits;
+    std::map<std::string, graphics_toolkit> m_loaded_toolkits;
   };
 }