ENH: enable user to control re-writing of function object output file headers. See #1556

src/OpenFOAM/db/functionObjects/writeFile/writeFile.H

@@ -82,6 +82,10 @@ protected:
         //- Flag to enable/disable writing to file
         bool writeToFile_;
 
+        //- Flag to update the header, e.g. on mesh changes.
+        //- Default is true.
+        bool updateHeader_;
+
         //- Flag to identify whether the header has been written
         bool writtenHeader_;
 
@@ -175,6 +179,9 @@ public:
         //- Flag to allow writing to file
         virtual bool writeToFile() const;
 
+        //- Flag to allow writing the header
+        virtual bool canWriteHeader() const;
+
         //- Return width of character stream output
         virtual label charWidth() const;