Implement variables_map::clear to clear extra members.

Fixes #4927


[SVN r67772]

Author: vprus

include/boost/program_options/variables_map.hpp

@@ -153,6 +153,9 @@ namespace boost { namespace program_options {
         // Resolve conflict between inherited operators.
         const variable_value& operator[](const std::string& name) const
         { return abstract_variables_map::operator[](name); }
+
+        // Override to clear some extra fields.
+        void clear(); 
 
         void notify();
 

src/variables_map.cpp

@@ -182,6 +182,13 @@ namespace boost { namespace program_options {
     : abstract_variables_map(next)
     {}
 
+    void variables_map::clear()
+    {
+        std::map<std::string, variable_value>::clear();
+        m_final.clear();
+        m_required.clear();
+    }
+
     const variable_value&
     variables_map::get(const std::string& name) const
     {