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📜  C++ STL-Multiset.erase()函数

📅  最后修改于: 2020-10-19 07:56:54             🧑  作者: Mango

C++ Multiset.erase()

C++ Multimultiset delete()函数用于从multiset容器中删除与给定键关联的单个元素或元素范围([first，last))。因此，将通过删除元素的数量来减小尺寸。

句法

void erase (iterator position);                             //until C++ 11
size_type erase (const value_type& val);              //until C++ 11
void erase (iterator first, iterator last);            //until C++ 11
iterator  erase (const_iterator position);          //since C++ 11
size_type erase (const value_type& val);          //since C++ 11    
iterator  erase (const_iterator first, const_iterator last); //since C++ 11

参数

position：迭代器，指向要从容器中删除的元素。

val：要从multiset容器中删除的值。

第一：擦除范围的开始。

last：要擦除范围的末尾。

返回值

delete()函数返回一个迭代器，该迭代器指向已删除元素的下一个元素或返回已删除元素的数量。

复杂度

擦除(位置)：摊销常数。

擦除(值)：容器大小的对数。

delete(first，last)：容器的第一个和最后一个之间的距离呈线性。

迭代器有效性

迭代器，引用和指向该函数删除的元素的指针均无效，其他所有迭代器，指针和引用均保持其有效性。

数据竞争

容器已修改。

删除的元素将被修改。尽管同时访问其他元素是安全的，但容器中的迭代范围并不安全。

异常安全

此函数不会引发异常。

如果指定了无效的范围或位置，则将导致未定义的行为。

例子1

让我们看一个简单的示例，该示例通过迭代器擦除元素。

#include 
#include 

using namespace std;

int main ()
{
  multiset mymultiset;
  multiset::iterator it;

  mymultiset = {10,20,30,20};
  
  cout<<"Before erasing the element: \n";
   for (it=mymultiset.begin(); it!=mymultiset.end(); ++it)
    cout << *it << '\n';

  it=mymultiset.find('b');
  mymultiset.erase (*it);                   // erasing by iterator

  cout<<"\nAfter erasing the element: \n";
  for (it=mymultiset.begin(); it!=mymultiset.end(); ++it)
    cout << *it << '\n';
    
  return 0;
}

输出：

Before erasing the element: 
10
20
20
30

After erasing the element: 
10
20
20
30

在上面的示例中，元素被迭代器“ it”擦除。

例子2

让我们看一个简单的示例，用给定的键值擦除multiset容器元素：

#include 
#include 

using namespace std;

int main ()
{
  multiset mymultiset;
  multiset::iterator it;

  mymultiset = {10, 20, 30, 40, 10, 30};
  
  cout<<"Before erasing the element: \n";
   for (it=mymultiset.begin(); it!=mymultiset.end(); ++it)
    cout << *it<< '\n';

   mymultiset.erase (30);                  // erasing by value

  cout<<"\nAfter erasing the element: \n";
  for (it=mymultiset.begin(); it!=mymultiset.end(); ++it)
    cout << *it<< '\n';
  return 0;
}

输出：

Before erasing the element: 
10
10
20
30
30
40

After erasing the element: 
10
10
20
40

在上面的示例中，delete(value)函数使用多重集中的值30。

例子3

让我们看一个简单的示例，以给定范围擦除元素：

#include 
#include 

using namespace std;

int main ()
{
  multiset mymultiset;
  multiset::iterator it;

  mymultiset = {10, 20, 30, 20};
  
  cout<<"Before erasing the element are: \n";
   cout<<"Size is: "<

输出：

Before erasing the element are: 
Size is: 3
10
20
30

After erasing the element are: 
Size is: 0

在上面的示例中，使用了Erase(first，last)函数来擦除具有给定范围(即开始到结束)的元素。

例子4

让我们看一个简单的示例，从multiset容器中删除所有奇数：

#include 
#include 

using namespace std;

int main()
{
    multiset m = {1,2,3,4,5,6,7,8,9,10,11,12,11,10,4};
                          
    // erase all odd numbers from m
    cout<<"After erasing odd numbers,elements are:\n ";
    for(auto it = m.begin(); it != m.end(); )
        if(*it % 2 == 1)
            it = m.erase(it);
        else
            ++it;
    for(auto& p : m)
        cout << p << ", ";
}

输出：

After erasing odd numbers, elements are:
 2, 4, 4, 6, 8, 10, 10, 12,

在上面的示例中，所有奇数均已删除，并显示偶数。

例子5

让我们看另一个例子：

#include   
#include   
#include   
#include  // next() and prev() helper functions  
  
using namespace std;  
  
using mymultiset = multiset;  
  
void printmultiset(const mymultiset& s) {  
    for (const auto& iter : s) {  
        cout << " [" << iter << "]";  
    }  
    cout << endl << "size() == " << s.size() << endl << endl;  
}  
  
int main()  
{  
    mymultiset s1;  
  
    // Fill in some data to test with, one at a time  
    s1.insert("Bob");  
    s1.insert("Robert");  
    s1.insert("Rob");  
    s1.insert("Rob");  
    s1.insert("Bob");  
  
    cout << "Starting data of multiset s1 is:" << endl;  
    printmultiset(s1);  
    // The 1st member function removes an element at a given position  
    s1.erase(next(s1.begin()));  
    cout << "After the 2nd element is deleted, the multiset s1 is:" << endl;  
    printmultiset(s1);  
  
    // Fill in some data to test with, one at a time, using an intializer list  
    mymultiset s2{ "meow", "nikita", "nikita", "growl", "yellow" };  
  
    cout << "Starting data of multiset s2 is:" << endl;  
    printmultiset(s2);  
    // The 2nd member function removes elements  
    // in the range [First, Last)  
    s2.erase(next(s2.begin()), prev(s2.end()));  
    cout << "After the middle elements are deleted, the multiset s2 is:" << endl;  
    printmultiset(s2);  
  
    mymultiset s3;  
  
    // Fill in some data to test with, one at a time, using emplace  
    s3.emplace("C");  
    s3.emplace("C#");  
    s3.emplace("D");  
    s3.emplace("D#");  
    s3.emplace("E");  
    s3.emplace("E#");  
    s3.emplace("F");  
    s3.emplace("F#");  
    s3.emplace("G");  
    s3.emplace("G#");  
    s3.emplace("E");  
    s3.emplace("E#");  
    s3.emplace("B");  
  
    cout << "Starting data of multiset s3 is:" << endl;  
    printmultiset(s3);  
    // The 3rd member function removes elements with a given Key  
    mymultiset::size_type count = s3.erase("E#");  
    // The 3rd member function also returns the number of elements removed  
    cout << "The number of elements removed from s3 is: " << count << "." << endl;  
    cout << "After the element with a key of \"E#\" is deleted, the multiset s3 is:" << endl;  
    printmultiset(s3);  
}

输出：

Starting data of multiset s1 is:
 [Bob] [Bob] [Rob] [Rob] [Robert]
size() == 5

After the 2nd element is deleted, the multiset s1 is:
 [Bob] [Rob] [Rob] [Robert]
size() == 4

Starting data of multiset s2 is:
 [growl] [meow] [nikita] [nikita] [yellow]
size() == 5

After the middle elements are deleted, the multiset s2 is:
 [growl] [yellow]
size() == 2

Starting data of multiset s3 is:
 [B] [C] [C#] [D] [D#] [E] [E] [E#] [E#] [F] [F#] [G] [G#]
size() == 13

The number of elements removed from s3 is: 2.
After the element with a key of "E#" is deleted, the multiset s3 is:
 [B] [C] [C#] [D] [D#] [E] [E] [F] [F#] [G] [G#]
size() == 11