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