From 3ea93f27aa8d02ddbd1fc24bb7e4564d0cab5721 Mon Sep 17 00:00:00 2001
From: Dan Rose <rotu@users.noreply.github.com>
Date: Fri, 20 Mar 2020 14:31:03 -0500
Subject: [PATCH] Prevent undefined behavior when serializing empty vector
 (#122)

Since m_get_const_function calls `std::vector<T>::operator[]`, accessing the zeroth element causes undefined behavior. Instead, return a null pointer to make the function behave sanely when vector is empty.
Fix #120
---
 rmw_cyclonedds_cpp/src/TypeSupport2.hpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/rmw_cyclonedds_cpp/src/TypeSupport2.hpp b/rmw_cyclonedds_cpp/src/TypeSupport2.hpp
index 0beadc1..55fceb7 100644
--- a/rmw_cyclonedds_cpp/src/TypeSupport2.hpp
+++ b/rmw_cyclonedds_cpp/src/TypeSupport2.hpp
@@ -245,6 +245,8 @@ public:
   }
   const void * sequence_contents(const void * ptr_to_sequence) const override
   {
+    if(sequence_size(ptr_to_sequence) == 0)
+      return nullptr;
     return m_get_const_function(ptr_to_sequence, 0);
   }
 };