c++ - use of undefined template type -

in following code

template<unsigned bits_count, typename ut_t, typename udt_t, template <typename> class meta_t> struct uint_t {     typedef uint_t<bits_count, ut_t, udt_t, meta_t> t;      typedef ut_t     ut;      typedef udt_t   udt;       typedef meta_t<t> meta;      ut comp[meta::array_count]; };  namespace mxi {  template<typename type> struct basic_info {     static const bool is_native = true;     static const bool is_signed = (type(-1) < type(0));      static const int num_of_bytes = sizeof(type);     static const int num_of_bits = sizeof(type) * 8; };  template<unsigned bits_count, typename ut_t, typename udt_t, template <typename> class meta_t> struct basic_info< uint_t<bits_count, ut_t, udt_t, meta_t> > {     static const bool is_native = false;     static const bool is_signed = false;      static const int num_of_bytes = bits_count / 8;     static const int num_of_bits = bits_count; };  template<typename t> struct isizeof {     static const int value = sizeof(t) * 8; };  template<typename t> struct num_of_dec_digits_in_type {     static const int value = int(isizeof<t>::value * 0.301f); };  template <typename type> struct default_meta {     static const int array_count = basic_info<type>::num_of_bits / isizeof<typename type::ut>::value;      static const int dec_digits_count = num_of_dec_digits_in_type<type>::value; };  }  int main() {     typedef uint_t<128, unsigned short int, unsigned int, mxi::default_meta> uint128_t;      int = uint128_t::meta::dec_digits_count;      int b = mxi::num_of_dec_digits_in_type<uint128_t>::value; } 

gcc 4.8.1 compiles without problem, visual c++ 2008 sp1 compile following error:

line (40): error c2027: use of undefined type 'uint_t<bits_count,ut_t,udt_t,meta_t>'         [         bits_count=128,         ut_t=unsigned short,         udt_t=unsigned int,         meta_t=mxi::default_meta     ]     line(46) : see reference class template instantiation 'mxi::isizeof<t>' being compiled         [         t=uint_t<128,unsigned short,unsigned int,mxi::default_meta>     ]     line(54) : see reference class template instantiation 'mxi::num_of_dec_digits_in_type<t>' being compiled         [         t=uint_t<128,unsigned short,unsigned int,mxi::default_meta>     ]     line(11) : see reference class template instantiation 'mxi::default_meta<type>' being compiled         [         type=uint_t<128,unsigned short,unsigned int,mxi::default_meta>     ]     line(63) : see reference class template instantiation 'uint_t<bits_count,ut_t,udt_t,meta_t>' being compiled         [         bits_count=128,         ut_t=unsigned short,         udt_t=unsigned int,         meta_t=mxi::default_meta     ] 

how uint_t not defined when it's first type defined in file?

note: i've stripped lot of code parts error, i.e. numbers here computed @ compile time, used them here directly keep focus in problem

well didn't understand why type not complete when i'm using complete type - i.e. uint128_t - able find 2 solutions:

1- in num_of_dec_digits_in_type replace isizeof<t>::value basic_info<t>::num_of_bits , it.

2- create new type num_of_dec_digits_in_type_size , use instead of num_of_dec_digits_in_type:

template<int size> struct num_of_dec_digits_in_type_size {     static const int value = int(size * 0.301f); };  template <typename type> struct default_meta {     .     .      static const int dec_digits_count = num_of_dec_digits_in_type_size< basic_info<type>::num_of_bits >::value; }; 

the 2nd solution modification of 1st solution.