Skip to content

iterator-traits-struct.md

Latest commit

 

History

History
147 lines (119 loc) · 3.72 KB

iterator-traits-struct.md

File metadata and controls

147 lines (119 loc) · 3.72 KB
title iterator_traits Struct | Microsoft Docs
ms.custom
ms.date 11/04/2016
ms.reviewer
ms.suite
ms.technology
cpp-standard-libraries
ms.tgt_pltfrm
ms.topic article
f1_keywords
xutility/std::iterator_traits
iterator_traits
dev_langs
C++
helpviewer_keywords
iterator_traits struct
iterator_traits class
ms.assetid 8b92c2c5-f658-402f-8ca1-e7ae301b8514
caps.latest.revision 19
author corob-msft
ms.author corob
manager ghogen
translation.priority.ht
cs-cz
de-de
es-es
fr-fr
it-it
ja-jp
ko-kr
pl-pl
pt-br
ru-ru
tr-tr
zh-cn
zh-tw

iterator_traits Struct

A template helper struct used to specify all the critical type definitions that an iterator should have.

Syntax

struct iterator_traits {
   typedef typename Iterator::iterator_category iterator_category;
   typedef typename Iterator::value_type value_type;
   typedef typename Iterator::difference_type difference_type;
   typedef difference_type distance_type;
   typedef typename Iterator::pointer pointer;
   typedef typename Iterator::reference reference;
   };

Remarks

The template struct defines the member types

  • iterator_category: a synonym for Iterator::iterator_category.

  • value_type: a synonym for Iterator::value_type.

  • difference_type: a synonym for Iterator::difference_type.

  • distance_type: a synonym for Iterator::difference_type.

  • pointer: a synonym for Iterator::pointer.

  • reference: a synonym for Iterator::reference.

The partial specializations determine the critical types associated with an object pointer of type Type * or const Type *.

In this implementation you can also use several template functions that do not make use of partial specialization:

template <class Category, class Type, class Diff>
C _Iter_cat(const iterator<Category, Ty, Diff>&);

template <class Ty>
random_access_iterator_tag _Iter_cat(const Ty *);

template <class Category, class Ty, class Diff>
Ty *val_type(const iterator<Category, Ty, Diff>&);

template <class Ty>
Ty *val_type(const Ty *);

template <class Category, class Ty, class Diff>
Diff *_Dist_type(const iterator<Category, Ty, Diff>&);

template <class Ty>
ptrdiff_t *_Dist_type(const Ty *);

which determine several of the same types more indirectly. You use these functions as arguments on a function call. Their sole purpose is to supply a useful template class parameter to the called function.

Example

// iterator_traits.cpp  
// compile with: /EHsc  
#include <iostream>  
#include <iterator>  
#include <vector>  
#include <list>  
  
using namespace std;  
  
template< class it >  
void  
function( it i1, it i2 )  
{  
   iterator_traits<it>::iterator_category cat;  
   cout << typeid( cat ).name( ) << endl;  
   while ( i1 != i2 )  
   {  
      iterator_traits<it>::value_type x;  
      x = *i1;  
      cout << x << " ";  
      i1++;  
   };     
   cout << endl;  
};  
  
int main( )   
{  
   vector<char> vc( 10,'a' );  
   list<int> li( 10 );  
   function( vc.begin( ), vc.end( ) );  
   function( li.begin( ), li.end( ) );  
}  
\* Output:   
struct std::random_access_iterator_tag  
a a a a a a a a a a   
struct std::bidirectional_iterator_tag  
0 0 0 0 0 0 0 0 0 0   
*\

Requirements

Header: <iterator>

Namespace: std

See Also

<iterator>
Thread Safety in the C++ Standard Library
C++ Standard Library Reference