1 files changed, 34 insertions, 5 deletions
diff --git a/libbutl/builtin-options.hxx b/libbutl/builtin-options.hxx
index b389298..6288e54 100644
--- a/libbutl/builtin-options.hxx
+++ b/libbutl/builtin-options.hxx
@@ -174,6 +174,14 @@ namespace butl
     // for the two previous arguments up until a call to a third
     // peek() or next().
     //
+    // The position() function returns a monotonically-increasing
+    // number which, if stored, can later be used to determine the
+    // relative position of the argument returned by the following
+    // call to next(). Note that if multiple scanners are used to
+    // extract arguments from multiple sources, then the end
+    // position of the previous scanner should be used as the
+    // start position of the next.
+    //
     class scanner
     {
       public:
@@ -191,13 +199,24 @@ namespace butl
 
       virtual void
       skip () = 0;
+
+      virtual std::size_t
+      position () = 0;
     };
 
     class argv_scanner: public scanner
     {
       public:
-      argv_scanner (int& argc, char** argv, bool erase = false);
-      argv_scanner (int start, int& argc, char** argv, bool erase = false);
+      argv_scanner (int& argc,
+                    char** argv,
+                    bool erase = false,
+                    std::size_t start_position = 0);
+
+      argv_scanner (int start,
+                    int& argc,
+                    char** argv,
+                    bool erase = false,
+                    std::size_t start_position = 0);
 
       int
       end () const;
@@ -214,7 +233,11 @@ namespace butl
       virtual void
       skip ();
 
-      private:
+      virtual std::size_t
+      position ();
+
+      protected:
+      std::size_t start_position_;
       int i_;
       int& argc_;
       char** argv_;
@@ -224,13 +247,15 @@ namespace butl
     class vector_scanner: public scanner
     {
       public:
-      vector_scanner (const std::vector<std::string>&, std::size_t start = 0);
+      vector_scanner (const std::vector<std::string>&,
+                      std::size_t start = 0,
+                      std::size_t start_position = 0);
 
       std::size_t
       end () const;
 
       void
-      reset (std::size_t start = 0);
+      reset (std::size_t start = 0, std::size_t start_position = 0);
 
       virtual bool
       more ();
@@ -244,7 +269,11 @@ namespace butl
       virtual void
       skip ();
 
+      virtual std::size_t
+      position ();
+
       private:
+      std::size_t start_position_;
       const std::vector<std::string>& v_;
       std::size_t i_;
     };