[ovs-dev] [PATCH] util: Update OVS_TYPEOF macro for Windows.

[Archana Holla]

Thanks Ben for the review comments.
Please find my answers for the questions and could you please take a look at v2 of patch with review commented addressed.
    
    >>Does this solve a problem?
     Yes,
      #define OBJECT_CONTAINING(POINTER, OBJECT, MEMBER) \
         ((OVS_TYPEOF(OBJECT)) (void *) \
         ((char *) (POINTER) - OBJECT_OFFSETOF(OBJECT, MEMBER)))
        
      On using ovs macro OBJECT_CONTAINING(which references OVS_TYPEOF), following compilation error is observed on windows C++ application:
      "
      error C2440: '=': cannot convert from 'void *' to 'object *'
      note: Conversion from 'void*' to pointer to non-'void' requires an explicit cast
       "
      With "decltype" keyword, this issue isn't seen as object is type casted to the right type.
    
    >>decltype is a C++ feature.  How is it specific to Windows?
      Agree with the review comment, as decltype is a C++ construct we can use it for all C++ enabled application, addressed in patch V2.
                        
    >>Please use #elif instead of introducing a nested #if...#endif.
      Yes, taken care in patch V2.
    
Thanks,
Archana
    
    
        On 3/19/20, 10:35 AM, "dev on behalf of Ben Pfaff" <ovs-dev-bounces at openvswitch.org on behalf of blp at ovn.org> wrote:
        
            On Thu, Mar 19, 2020 at 10:03:15AM -0700, Archana Holla via dev wrote:
            > OVS_TYPEOF macro doesn’t return the type of object for non __GNUC__ platforms.
            > Updating it for _WIN32 platforms when used from C++ code.
            > 
            > Signed-off-by: Archana Holla <harchana at vmware.com>
            > ---
            >  include/openvswitch/util.h | 4 ++++
            >  1 file changed, 4 insertions(+)
            > 
            > diff --git a/include/openvswitch/util.h b/include/openvswitch/util.h
            > index 9189e64..af7d1b0 100644
            > --- a/include/openvswitch/util.h
            > +++ b/include/openvswitch/util.h
            > @@ -86,8 +86,12 @@ OVS_NO_RETURN void ovs_assert_failure(const char *, const char *, const char *);
            >  #ifdef __GNUC__
            >  #define OVS_TYPEOF(OBJECT) typeof(OBJECT)
            >  #else
            > +#if defined (__cplusplus) && defined(_WIN32)
            > +#define OVS_TYPEOF(OBJECT) decltype(OBJECT)
            > +#else
            >  #define OVS_TYPEOF(OBJECT) void *
            >  #endif
            > +#endif
            
            Thanks for submitting a patch.
            
            Does this solve a problem?
            
            decltype is a C++ feature.  How is it specific to Windows?
            
            Please use #elif instead of introducing a nested #if...#endif.
            
            Thanks,
            
            Ben.
            _______________________________________________
            dev mailing list
            dev at openvswitch.org
            https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.openvswitch.org%2Fmailman%2Flistinfo%2Fovs-dev&data=02%7C01%7Ckumaranand%40vmware.com%7C0a5436579e8649e0f82808d7cc2be960%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637202361299974072&sdata=9MXAsT5tmBCUNKNrccv0knGJe5MLeXy8RGWvpIncd9g%3D&reserved=0