simple-binary-encoding: [C++] Undefined behaviour in generated code

The C++ code generator typically generates code like this for accessing integer fields:

    std::int32_t securityID(void) const
    {
        return SBE_LITTLE_ENDIAN_ENCODE_32(*((std::int32_t *)(m_buffer + m_offset + 24)));
    }

    NewOrderSingle &securityID(const std::int32_t value)
    {
        *((std::int32_t *)(m_buffer + m_offset + 24)) = SBE_LITTLE_ENDIAN_ENCODE_32(value);
        return *this;
    }

The compiler assumes that a pointer to a int32_t has the correct alignment. With this generated code the alignment requirement might not fulfilled. On amd64 this is fine as long as the compiler doesn’t try to use SSE or AVX instructions, but it’s not safe in general to assume it will work.

The solution is to use memcpy like this (https://chromium.googlesource.com/chromium/src.git/+/master/base/bit_cast.h):

template <class Dest, class Source>
inline Dest bit_cast(const Source& source) {
   static_assert(sizeof(Dest) == sizeof(Source),
   "bit_cast requires source and destination to be the same size");
   static_assert(base::is_trivially_copyable<Dest>::value,
   "bit_cast requires the destination type to be copyable");
   static_assert(base::is_trivially_copyable<Source>::value,
   "bit_cast requires the source type to be copyable");
    
   Dest dest;
   memcpy(&dest, &source, sizeof(dest));
   return dest;
}

This should optimize to a single load load on amd64, guaranteed not to use instructions requiring alignment.