c++ - Why can't i use struct nested in a struct as a type to declare variable in a class template? -

this question has answer here:

• where , why have put “template” , “typename” keywords? 5 answers

you see, structs, put structs inside structs , try use these nested structs in class template declare variables. problem is: doesn't seem work expected. minimal example code:

#include "stdafx.h" #include <iostream>  struct t1 {     struct nested     {         int var1 = 12345;     }; };  struct t2 {     struct nested     {         float var1 = 67890;     }; };   template <typename t > class proletarian { public:     t * t;                                       //works   //t::nested * tn;        ****** doesn't work! *******     proletarian<typename t>()     {         t::nested * tnested = new t::nested;     //works         std::cout << tnested->var1;     }  };  int _tmain(int argc, _tchar* argv[]) {     proletarian<t1> t1 = proletarian<t1>();     proletarian<t2> t2 = proletarian<t2>();      return 0; } 

i use visual studio 2013, intellisense ok code, won't compile these 2 errors:

[line 20 column 1] error c2143: syntax error : missing ';' before '*'

[line 20 column 1] error c4430: missing type specifier - int assumed. note: c++ not support default-int

i'm not @ c++, don't quite understand how templates work , why happens.

when compiler first passes on proletarian - before sees instantiation specific type t - need know t::nested refer type, can give using typename follows:

template <typename t> class proletarian {   public:     typename t::nested* tn;     proletarian<t>()     {         typename t::nested* tnested = new typename t::nested;         std::cout << tnested->var1;     } };