I have the following code which compiles successfully in c++14.
template<class T, class ...Args> class B { public: using AbcData = int; }; template<typename ...Args> class D : public B<float, Args...> { public: AbcData m_abc; }; But when compiled in c++17, it gives the following error.
error C2061: syntax error: identifier 'AbcData' What is wrong with the code and how to fix this?
When the base class B class depends upon the template parameters, even though derived class D here type alias AbcData inherited from the B, using simply AbcData in D class, is not enough.
You need to be explicit, from where you have it
template<typename ...Args> class D : public B<float, Args...> { public: typename B<float, Args...>::AbcData m_abc; // --> like this }; 
AbcData is not ambiguous, you can use D itself instead of the base class B<float, Args...> to make the name dependent. That might be more straight-forward.AbcData multiple times so i used using AbcData = B<float, Args...>::AbcData. it's working now. is there better alternative that is shorter and less specifying too much redundant details? i also have other data types from base class not just AbcData.typename before B and you can use using typename B<float, Args...>::AbcData; instead.
/Za, maybe they have an extension or something.