From c50461528c857a4ef7d97d852014bd8dc1f3cac4 Mon Sep 17 00:00:00 2001
From: joaquintides <joaquin@tid.es>
Date: Mon, 6 Mar 2023 13:50:25 +0100
Subject: [PATCH] fixed UB with begin when using fast iteration

---
 include/boost/unordered/detail/foa.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/boost/unordered/detail/foa.hpp b/include/boost/unordered/detail/foa.hpp
index 63b43ee4..c4d8b56f 100644
--- a/include/boost/unordered/detail/foa.hpp
+++ b/include/boost/unordered/detail/foa.hpp
@@ -1457,7 +1457,7 @@ public:
   iterator begin()noexcept
   {
     iterator it{arrays.groups,0,arrays.elements};
-    if(!(arrays.groups[0].match_occupied()&0x1))++it;
+    if(arrays.elements&&!(arrays.groups[0].match_occupied()&0x1))++it;
     return it;
   }