add new test stringstyle() for identify variable styles that return stored strings directly

src/variable.cpp

@@ -804,6 +804,19 @@ int Variable::internalstyle(int ivar)
   return 0;
 }
 
+/* ----------------------------------------------------------------------
+   return 1 if variable is INDEX or WORLD or STRING or SCALARFILE, 0 if not
+   this is used to discriminate between variables that return a pointer to
+   the stored string and others that do evaluations or return numbers.
+------------------------------------------------------------------------- */
+
+int Variable::stringstyle(int ivar)
+{
+  if (style[ivar] == INDEX || style[ivar] == WORLD
+      || style[ivar] == STRING || style[ivar] == SCALARFILE) return 1;
+  return 0;
+}
+
 /* ----------------------------------------------------------------------
    return ptr to the data text associated with a variable
    if INDEX or WORLD or UNIVERSE or STRING or SCALARFILE,

src/variable.h

@@ -38,6 +38,7 @@ class Variable : protected Pointers {
   int vectorstyle(int);
   char *pythonstyle(char *, char *);
   int internalstyle(int);
+  int stringstyle(int);
 
   char *retrieve(char *);
   double compute_equal(int);