From c2d90db660f780b7258e5ae2d9063607c0496df7 Mon Sep 17 00:00:00 2001
From: Jonny <21113168+Jonny0201@users.noreply.github.com>
Date: Sat, 26 Jul 2025 14:11:35 +0800
Subject: [PATCH] Update listing_7.5.cpp - Undefined behaviour

If `old_head` is a null pointer, `chain_pending_node` will read the member variable `next` from a null pointer.
---
 listings/listing_7.5.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/listings/listing_7.5.cpp b/listings/listing_7.5.cpp
index b4e44c5..e172054 100644
--- a/listings/listing_7.5.cpp
+++ b/listings/listing_7.5.cpp
@@ -31,7 +31,10 @@ class lock_free_stack
         }
         else
         {
-            chain_pending_node(old_head);
+            if(old_head)
+            {
+                chain_pending_node(old_head);
+            }
             --threads_in_pop;
         }
     }