random_access_iterator_tag 结构

一个为代表随机访问迭代器的 iterator_category 函数提供返回类型的类。

语法

struct random_access_iterator_tag    : public bidirectional_iterator_tag {};

备注

分类标记类用作算法选择的编译标记。 模板函数需要查找其迭代器参数的最特定的类别，以便可以在编译时使用最高效的算法。 对于每个 Iterator 类型的迭代器，iterator_traits<Iterator>::iterator_category 必须定义为最具体的分类标记，用于描述迭代器的行为。

当 Iter 描述一个可充当随机访问迭代器的对象时，其类型与 iterato<Iter>::iterator_category 相同。

示例

// iterator_rait.cpp
// compile with: /EHsc
#include <iterator>
#include <vector>
#include <iostream>
#include <list>

using namespace std;

int main( )
{
   vector<int> vi;
   vector<char> vc;
   list<char> lc;
   iterator_traits<vector<int>:: iterator>::iterator_category cati;
   iterator_traits<vector<char>:: iterator>::iterator_category catc;
   iterator_traits<list<char>:: iterator>::iterator_category catlc;

   // These are both random-access iterators
   cout << "The type of iterator for vector<int> is "
       << "identified by the tag:\n "
       << typeid ( cati ).name( ) << endl;
   cout << "The type of iterator for vector<char> is "
       << "identified by the tag:\n "
       << typeid ( catc ).name( ) << endl;
   if ( typeid ( cati ) == typeid( catc ) )
      cout << "The iterators are the same." << endl << endl;
   else
      cout << "The iterators are not the same." << endl << endl;

   // But the list iterator is bidirectinal, not random access
   cout << "The type of iterator for list<char> is "
       << "identified by the tag:\n "
       << typeid (catlc).name( ) << endl;

   // cout << ( typeid ( vi.begin( ) ) == typeid( vc.begin( ) ) ) << endl;
   if ( typeid ( vi.begin( ) ) == typeid( vc.begin( ) ) )
      cout << "The iterators are the same." << endl;
   else
      cout << "The iterators are not the same." << endl;
   // A random-access iterator is a bidirectional iterator.
   cout << ( void* ) dynamic_cast< iterator_traits<list<char>:: iterator>
          ::iterator_category* > ( &catc ) << endl;
}

示例输出

以下输出面向 x86。

The type of iterator for vector<int> is identified by the tag:
    struct std::random_access_iterator_tag
The type of iterator for vector<char> is identified by the tag:
    struct std::random_access_iterator_tag
The iterators are the same.

The type of iterator for list<char> is identified by the tag:
    struct std::bidirectional_iterator_tag
The iterators are not the same.
0012FF3B

要求

标头：<iterator>

命名空间： std

另请参阅

bidirectional_iterator_tag 结构
C++ 标准库中的线程安全
C++ 标准库参考