C++ multimap rend()
C++ multimap rend()函数
C++ multimap rend()函数用于将迭代器返回到multimap的末尾(而不是倒数第二个元素,最后一个过去的元素)。与非反转容器的第一个元素前面的元素相似。
注意: 注意: 这是一个占位符。此位置没有元素,尝试访问是未定义的行为。
语法
reverse_iterator rend(); //until C++ 11
const_reverse_iterator rend() const; //until C++ 11
reverse_iterator rend() nothrow; //since C++ 11
const_reverse_iterator rend() const nothrow; //since C++ 11
参数
无
返回值
它将反向迭代器返回到最后一个元素之后的元素
复杂度
常量。
迭代器有效性
否更改。
数据竞争
已访问容器。
异常安全
此函数从不抛出异常。
示例1
让我们看一下rend()函数的简单示例:
#include <iostream>
#include <map>
using namespace std;
int main ()
{
multimap<char,int> mymultimap;
mymultimap = {
{'a', 100},
{'b', 200},
{'c', 100},
{'b', 400}
};
// show content:
multimap<char,int>::reverse_iterator rit;
for (rit=mymultimap.rbegin(); rit!=mymultimap.rend(); ++rit)
cout << rit->first << " = " << rit->second << '\n';
return 0;
}
输出:
c = 100
b = 400
b = 200
a = 100
在上面的示例中,rend()函数用于将反向迭代器返回到反转容器的最后一个元素之后的元素。
因为 set 映射因此按键的排序顺序存储元素,则在 multimap 上进行迭代将导致上述顺序,即键的排序顺序。
示例2
让我们看一个简单的示例,以相反的顺序在 multimap 上进行迭代使用while循环:
#include <iostream>
#include <map>
#include <string>
#include <iterator>
using namespace std;
int main() {
// Creating & Initializing a multimap of String & Ints
multimap<string, int> multimapEx = {
{ "aaa", 10 },
{ "ddd", 11 },
{ "aaa", 12 },
{ "ccc", 13 }
};
// Create a multimap iterator and point to the end of multimap
multimap<string, int>::reverse_iterator it = multimapEx.rbegin();
// Iterate over the multimap using Iterator till beginning.
while (it != multimapEx.rend()) {
// Accessing KEY from element pointed by it.
string word = it->first;
// Accessing VALUE from element pointed by it.
int count = it->second;
cout << word << " :: " << count << endl;
// Increment the Iterator to point to next entry
it++;
}
return 0;
}
输出:
ddd :: 11
ccc :: 13
aaa :: 12
aaa :: 10
在上面的示例中,我们使用while循环以相反的顺序迭代 multimap 。
因为 multimap 按键的排序顺序存储元素,所以在 multimap 上迭代将导致顺序,即键的排序顺序。
示例3
让我们看一个简单的示例
#include <map>
#include <iostream>
int main( )
{
using namespace std;
multimap <int, int> m1;
multimap <int, int> :: iterator m1_Iter;
multimap <int, int> :: reverse_iterator m1_rIter;
multimap <int, int> :: const_reverse_iterator m1_crIter;
typedef pair <int, int> Int_Pair;
m1.insert ( Int_Pair ( 1, 10 ) );
m1.insert ( Int_Pair ( 2, 20 ) );
m1.insert ( Int_Pair ( 3, 30 ) );
m1_rIter = m1.rend( );
m1_rIter--;
cout << "The last element of the reversed multimap m1 is "
<< m1_rIter-> first << "." << endl;
// begin can be used to start an iteration
// through a multimap in a forward order
cout << "The multimap is: ";
for ( m1_Iter = m1.begin( ) ; m1_Iter != m1.end( ); m1_Iter++)
cout << m1_Iter-> first << " ";
cout << "." << endl;
// rbegin can be used to start an iteration
// throught a multimap in a reverse order
cout << "The reversed multimap is: ";
for ( m1_rIter = m1.rbegin( ) ; m1_rIter != m1.rend( ); m1_rIter++)
cout << m1_rIter-> first << " ";
cout << "." << endl;
// A multimap element can be erased by dereferencing to its key
m1_rIter =--m1.rend( );
m1.erase ( m1_rIter-> first );
m1_rIter = m1.rend( );
m1_rIter--;
cout << "After the erasure, the last element "
<< "in the reversed multimap is "
<< m1_rIter-> first << "." << endl;
return 0;
}
输出:
The last element of the reversed multimap m1 is 1.
The multimap is: 1 2 3 .
The reversed multimap is: 3 2 1 .
After the erasure, the last element in the reversed multimap is 2.
在上面的示例中, multimap 的元素以相反的顺序返回。
示例4
让我们看一个简单的示例来排序和计算最高薪水:
#include <iostream>
#include <string>
#include <map>
using namespace std;
int main ()
{
multimap<int,int> emp = {
{ 1000, 10},
{ 3500, 20 },
{ 4500, 30 },
{ 3000, 40 },
{ 3500, 50 }};
cout << "Salary" << " | " << "ID" << '\n';
cout<<"______________________\n";
multimap<int,int>::reverse_iterator rit;
for (rit=emp.rbegin(); rit!=emp.rend(); ++rit)
cout << rit->first << " | " << rit->second << '\n';
auto ite = emp.rbegin();
cout << "\nHighest salary: "<< ite->first <<" \n";
cout << "ID is: "<< ite->second << "\n";
return 0;
}
输出:
Salary | ID
______________________
4500 | 30
3500 | 50
3500 | 20
3000 | 40
1000 | 10
Highest salary: 4500
ID is: 30
在上面的示例中,实现了一个multimap emp,其中,ID作为值存储,而薪水作为键存储。这使我们能够利用多地图中的自动排序功能,并使我们能够确定薪水最高的元素的ID。