包含测试 [英] Test for inclusion
问题描述
我有两个已分类的容器，我想知道第二个容器中是否存在来自一个
容器的任何项目。
标准库中有什么要做的吗？
谢谢
I have two sorted containers, and I wish to know if any items from one
container exist in the second container. Is there anything in the
standard library to do this?
Thanks
推荐答案
set_intersection怎么样？
http://www.sgi.com/tech/stl/set_intersection.html
Moohoo写道：
How about set_intersection?
http://www.sgi.com/tech/stl/set_intersection.html
Moohoo wrote:
我有两个已分类的容器，我想知道第二个容器中是否存在来自一个
容器的任何项目。
标准库中有什么要做的吗？
谢谢
I have two sorted containers, and I wish to know if any items from one
container exist in the second container. Is there anything in the
standard library to do this?
Thanks
Moohoo写道：
Moohoo wrote:
我有两个已分类的容器，我想知道第二个容器中是否有来自一个
容器的任何物品。
标准库中有什么可以做到的吗？
I have two sorted containers, and I wish to know if any items from one
container exist in the second container. Is there anything in the
standard library to do this?
您可以使用std :: set_intersection（）。如果你只对
的交集感兴趣，你可以使用一个output_iterator，当std :: set_intersection（）写入第一个元素时，它会立即抛出
：
#include< set>
#include< algorithm>
#include< iterator>
模板< typename T>
struct throwing_iterator
：public std :: iterator< std :: output_iterator_tag，void，void，void，void>
{
struct flag_type {};
throw_iterator& operator =（T const& value）{
throw（flag_type（））;
}
throwing_iterator& operator *（void）{
return（* this）;
}
throwing_iterator& operator ++（void）{
return（* this）;
}
throwing_iterator& operator ++（int）{
return（* this）;
}
}; // throwing_iterator
template< typename Iterator>
bool has_intersection（Iterator from1，Iterator to1，
Iterator from2，Iterator to2）{
typedef typename std :: iterator_traits< ; Iterator> :: value_type value_type;
throwing_iterator< value_type t_iter;
尝试{
std :: set_intersection（from1，to1，from2，to2，t_iter）;
}
catch（typename throwing_iterator< value_type> :: flag_type）{
return（true）;
}
return（false ）;
}
请注意，这有点不正统。
更传统的方法是迭代一个范围并使用一个
的各种二进制搜索方法（std :: lower_bound（），std :: upper_bound，
std :: binary_search（））来查找元素另一个范围。
最好
Kai-Uwe Bux
You could use std::set_intersection(). If you are only interested in whether
the intersection is empty, you could use an output_iterator that throws as
soon as the std::set_intersection() writes the first element:
#include <set>
#include <algorithm>
#include <iterator>
template < typename T >
struct throwing_iterator
: public std::iterator< std::output_iterator_tag, void, void, void, void >
{
struct flag_type {};
throwing_iterator & operator= ( T const & value ) {
throw ( flag_type() );
}
throwing_iterator & operator* ( void ) {
return ( *this );
}
throwing_iterator & operator++ ( void ) {
return ( *this );
}
throwing_iterator & operator++ ( int ) {
return ( *this );
}
}; // throwing_iterator
template < typename Iterator >
bool has_intersection ( Iterator from1, Iterator to1,
Iterator from2, Iterator to2 ) {
typedef typename std::iterator_traits< Iterator >::value_type value_type;
throwing_iterator< value_type t_iter;
try {
std::set_intersection( from1, to1, from2, to2, t_iter );
}
catch ( typename throwing_iterator< value_type >::flag_type ) {
return ( true );
}
return ( false );
}
Note that this is a little unorthodox.
An more conventional method would be to iterate over one range and use one
of the various binary search methods (std::lower_bound(), std::upper_bound,
std::binary_search()) to find the element in the other range.
Best
Kai-Uwe Bux
我不知道如果我鼓励使用例外 - 当然
空交叉口不是特殊状态，除非你在没有检查它是否包含任何内容的情况下访问它。
您可以制作一个临时容器，看看它被放入
吧。如果您持有非常大的对象，也许您可以将它们放在一个带有boost :: shared_ptr的容器中，以防止将一个大对象复制到一个临时集合中 -
只复制一个shared_ptr。
下限的东西也可以。
-J
Kai-Uwe Bux写道：
I don''t know if I would encourage this use of an exception - certainly
an empty intersection is not an exceptional state, unless you were
accessing it without checking to see if it contained anything.
You could just make a temporary container and see what gets put into
it. If you are holding very large objects, perhaps you could put them
in a container with boost::shared_ptr to prevent copying a large object
to a temporary set - you would only copy a shared_ptr.
The lower-bound thing would work, also.
-J
Kai-Uwe Bux wrote:
Moohoo写道：
Moohoo wrote:
我有两个已分类的容器，并且我想知道第二个容器中是否存在来自一个
容器的任何物品。
标准库中有什么可以做到的吗？
I have two sorted containers, and I wish to know if any items from one
container exist in the second container. Is there anything in the
standard library to do this?
您可以使用std :: set_intersection（）。如果你只对
的交集感兴趣，你可以使用一个output_iterator，当std :: set_intersection（）写入第一个元素时，它会立即抛出
：
#include< set>
#include< algorithm>
#include< iterator>
模板< typename T>
struct throwing_iterator
：public std :: iterator< std :: output_iterator_tag，void，void，void，void>
{
struct flag_type {};
throw_iterator& operator =（T const& value）{
throw（flag_type（））;
}
throwing_iterator& operator *（void）{
return（* this）;
}
throwing_iterator& operator ++（void）{
return（* this）;
}
throwing_iterator& operator ++（int）{
return（* this）;
}
}; // throwing_iterator
模板< typename Iterator>
bool has_intersection（Iterator from1，Iterator to1，
Iterator from2，Iterator to2）{
typedef typename std :: iterator_traits< ; Iterator> :: value_type value_type;
throwing_iterator< value_type t_iter;
尝试{
std :: set_intersection（from1，to1，from2，to2，t_iter）;
}
catch（typename throwing_iterator< value_type> :: flag_type）{
return（true）;
}
return（false ）;
}
请注意，这有点不正统。
更常规的方法是迭代一个范围并使用一个
的各种二进制搜索方法（std :: lower_bound（），std :: upper_bound，
std :: binary_search（））来找到其他范围内的元素。
最好
Kai-Uwe Bux
You could use std::set_intersection(). If you are only interested in whether
the intersection is empty, you could use an output_iterator that throws as
soon as the std::set_intersection() writes the first element:
#include <set>
#include <algorithm>
#include <iterator>
template < typename T >
struct throwing_iterator
: public std::iterator< std::output_iterator_tag, void, void, void, void >
{
struct flag_type {};
throwing_iterator & operator= ( T const & value ) {
throw ( flag_type() );
}
throwing_iterator & operator* ( void ) {
return ( *this );
}
throwing_iterator & operator++ ( void ) {
return ( *this );
}
throwing_iterator & operator++ ( int ) {
return ( *this );
}
}; // throwing_iterator
template < typename Iterator >
bool has_intersection ( Iterator from1, Iterator to1,
Iterator from2, Iterator to2 ) {
typedef typename std::iterator_traits< Iterator >::value_type value_type;
throwing_iterator< value_type t_iter;
try {
std::set_intersection( from1, to1, from2, to2, t_iter );
}
catch ( typename throwing_iterator< value_type >::flag_type ) {
return ( true );
}
return ( false );
}
Note that this is a little unorthodox.
An more conventional method would be to iterate over one range and use one
of the various binary search methods (std::lower_bound(), std::upper_bound,
std::binary_search()) to find the element in the other range.
Best
Kai-Uwe Bux
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