Add method to copy entire properry subtree

simgear/props/props.cxx

@@ -2443,6 +2443,7 @@ SGPropertyNode::fireValueChanged (SGPropertyNode * node)
 {
   if (_listeners != 0) {
     for (unsigned int i = 0; i < _listeners->size(); i++) {
+        if ((*_listeners)[i])
             (*_listeners)[i]->valueChanged(node);
     }
   }
@@ -2630,6 +2631,30 @@ bool compareNodeValue(const SGPropertyNode& lhs, const SGPropertyNode& rhs)
     }
 }
 
+
+void SGPropertyNode::copy(SGPropertyNode *to)
+{
+    if (nChildren())
+    {
+        for (int i = 0; i < nChildren(); i++) {
+            SGPropertyNode *child = getChild(i);
+            SGPropertyNode *to_child = to->getChild(child->getName());
+            if (!to_child)
+                to_child = to->addChild(child->getName());
+            if (child->nChildren())
+            {
+                child->copy(to_child);
+            }
+            else
+            {
+                to_child->setValue(child->getStringValue());
+            }
+        }
+    }
+    else
+        to->setValue(getStringValue());
+}
+
 bool SGPropertyNode::compare(const SGPropertyNode& lhs,
                              const SGPropertyNode& rhs)
 {

simgear/props/props.hxx

@@ -1105,6 +1105,11 @@ public:
    */
   SGPropertyNode * getNode (const char * relative_path, bool create = false);
 
+  /**
+  * deep copy one node to another.
+  */
+  void copy(SGPropertyNode *to);
+
   /**
    * Get a pointer to another node by relative path.
    */