c++ - difference_type が見つかりません

Answer 1

必要な型/演算子をすべて定義しようとしましたか?

#include <iterator>

struct nit
{
  typedef std::random_access_iterator_tag iterator_category;
  typedef int value_type;
  typedef int difference_type;
  typedef int* pointer;
  typedef int& reference;

  bool operator==(nit const&)
  {
    return true;
  }

  bool operator!=(nit const&)
  {
    return false;
  }

  int operator-(nit const&)
  {
    return 0;
  }

  nit()
  {
  }
};

int main()
{
  nit const test1;
  std::distance(test1, test1);

  return 0;
}

Answer 2

std::iterator_traits が期待するクラスですべての typedef (std::iterator の助けを借りて、または使わずに) を提供するか、std::iterator_traits を自分で特殊化する必要があります。

このバージョンの GCC は他のエラー メッセージを出力しますが、コードが違法であるという事実は変わりません。

prog.cpp: In function ‘int main()’:
prog.cpp:9: error: uninitialized const ‘test1’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++v4/bits/stl_iterator_base_types.h: At global scope:
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h: In instantiation of ‘std::iterator_traits<nit>’:
prog.cpp:10:   instantiated from here
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h:133: error: no type named ‘iterator_category’ in ‘class nit’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h:134: error: no type named ‘value_type’ in ‘class nit’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h:136: error: no type named ‘pointer’ in ‘class nit’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h:137: error: no type named ‘reference’ in ‘class nit’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_funcs.h: In function ‘typename std::iterator_traits<_Iterator>::difference_type std::distance(_InputIterator, _InputIterator) [with _InputIterator = nit]’:
prog.cpp:10:   instantiated from here
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_funcs.h:119: error: no matching function for call to ‘__iterator_category(nit&)’