[C++] Implement subst and strip
diff --git a/strutil.h b/strutil.h
index 7369787..0b84f1e 100644
--- a/strutil.h
+++ b/strutil.h
@@ -34,6 +34,7 @@
 class WordWriter {
  public:
   explicit WordWriter(string* o);
+  void MaybeAddWhitespace();
   void Write(StringPiece s);
 
  private: