make the avl node key const

diff --git a/avl.h b/avl.h
index a563716e1d5f43fd71e4931939176863e101e8ca..46a396f2d6d55191d9e3117f563726c0d4ac8a23 100644 (file)
--- a/avl.h
+++ b/avl.h
@@ -82,7 +82,7 @@ struct avl_node {
   /**
    * pointer to key of node
    */
-  void *key;
+  const void *key;
 
   /**
    * balance state of AVL tree (0,-1,+1)