C++ multiset equal_range()
C++ multiset equal_range()
C++ multiset 合 equal_range()函数用于返回包含容器中所有元素的范围边界等于val。
如果val与容器中的任何值都不匹配，则返回值范围将为长度0，并且两个迭代器均指向大于val的最近值。否则，如果val大于容器中的所有元素，则指向结束。
语法
pair<const_iterator,const_iterator> equal_range (const value_type& val) const;
pair<iterator,iterator> equal_range (const value_type& val);
范围由两个迭代器定义，一个指向不小于值val的第一个元素，另一个指向大于值val的第一个元素。
参数
val : 要在 multiset 容器中搜索的值。
返回值
此函数返回对。其中pair :: first位于范围的下边界，具有与lower_bound(val)将返回的值相同的值，pair :: second是与upper_bound(val)将返回的值相同，它对应的范围的上限。
复杂度
大小为对数。
迭代器有效性
没有变化。
数据争用
访问容器(无论是const还是非const版本都不能修改容器)。
同时访问 multiset 的元素是安全的。
异常安全性
如果引发异常，则在
示例1
让我们看一个简单的示例:
#include <iostream>
#include <set>
using namespace std;
int main(void) {
multiset<char> m = {'a','b','c','a'};
auto ret = m.equal_range('b');
cout << "Lower bound of b is: " << *ret.first<< endl;
cout << "Upper bound of b is: " << *ret.second<< endl;
return 0;
}
输出:
Lower bound of b is: b
Upper bound of b is: c
在上面的示例中，b的下限是b，b的上限是c。
示例2
我们来看一个简单的示例:
#include <iostream>
#include <set>
using namespace std;
int main()
{
// initialize container
multiset<int> mp;
// insert elements in random order
mp.insert( 4 );
mp.insert( 1 );
mp.insert( 4 );
pair<multiset<int>::const_iterator,multiset<int>::const_iterator> ret;
ret = mp.equal_range(10);
cout << "The lower bound is: " << *ret.first;
cout << "\nThe upper bound is: " << *ret.second;
return 0;
}
输出:
The lower bound is 3
The upper bound is 3
在上面的示例中，equal_range()函数返回到end()，即3，因为它试图查找10在 multiset mp中不存在的值，因此，它返回到结尾。
示例3
让我们看一个简单的示例:
#include <set>
#include <iostream>
int main( )
{
using namespace std;
typedef multiset<int, less< int > > IntMultiset;
IntMultiset s1;
multiset <int, less< int > > :: const_iterator s1_RcIter;
s1.insert( 10 );
s1.insert( 20 );
s1.insert( 30 );
pair <IntMultiset::const_iterator, IntMultiset::const_iterator> p1, p2;
p1 = s1.equal_range( 20 );
cout << "The upper bound of the element with "
<< "a key of 20 in the multiset s1 is: "
<< *(p1.second) << "." << endl;
cout << "The lower bound of the element with "
<< "a key of 20 in the multiset s1 is: "
<< *(p1.first) << "." << endl;
// Compare the upper_bound called directly
s1_RcIter = s1.upper_bound( 20 );
cout << "A direct call of upper_bound( 20 ) gives "
<< *s1_RcIter << "," << endl
<< "matching the 2nd element of the pair"
<< " returned by equal_range( 20 )." << endl;
p2 = s1.equal_range( 40 );
// if no match is found for the key,
// both elements of the pair return end( )
if ( ( p2.first == s1.end( ) ) && ( p2.second == s1.end( ) ) )
cout << "The multiset s1 doesn't have an element "
<< "with a key less than 40." << endl;
else
cout << "The element of multiset s1 with a key >= 40 is: "
<< *(p1.first) << "." << endl;
return 0;
}
输出:
The upper bound of the element with a key of 20 in the multiset s1 is: 30.
The lower bound of the element with a key of 20 in the multiset s1 is: 20.
A direct call of upper_bound( 20 ) gives 30,
matching the 2nd element of the pair returned by equal_range( 20 ).
The multiset s1 doesn't have an element with a key less than 40.
示例4
让我们看一个简单的示例:
#include <iostream>
#include <set>
using namespace std;
int main ()
{
std::multiset<int> mymultiset;
for (int i=1; i<=5; i++) mymultiset.insert(i*10); // mymultiset: 10 20 30 40 50
pair<std::multiset<int>::const_iterator,multiset<int>::const_iterator> ret;
ret = mymultiset.equal_range(30);
cout << "the lower bound points to: " << *ret.first << '\n';
cout << "the upper bound points to: " << *ret.second << '\n';
return 0;
}
输出:
the lower bound points to: 30
the upper bound points to: 40
