C++

参考

<unordered_map>

unordered_multimap

public member function
<unordered_map>

std::unordered_multimap::erase

by position (1)
iterator erase ( const_iterator position );
by key (2)
size_type erase ( const key_type& k );
range (3)
iterator erase ( const_iterator first, const_iterator last );
Erase elements
Removes from the unordered_multimap container either the elements whose key is k or those in a range ([first,last)).

This effectively reduces the container size by the number of elements removed, calling each element's destructor.

参数

position
Iterator pointing to a single element to be removed from the unordered_multimap.
成员类型const_iterator是一个 forward iterator 类型。
k
Key of the elements to be erased.
成员类型key_type是容器中元素的键的类型，在 unordered_multimap 中定义为其第一个模板参数（键).
first, last
Iterators specifying a range within the unordered_multimap container to be removed[first,last). i.e., the range includes all the elements between first and last, including the element pointed by first but not the one pointed by last.
Notice that unordered_multimap containers do not follow any particular order to organize its elements, therefore the effect of range deletions may not be easily predictable.
成员类型const_iterator是一个 forward iterator 类型。

返回值

Versions (1) and (3) return an iterator pointing to the position immediately following the last of the elements erased.
Version (2) returns the number of elements erased.

成员类型iterator是一个 forward iterator 类型。
成员类型size_type是一种无符号整型类型。

示例

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// unordered_multimap::erase
#include <iostream>
#include <unordered_map>

int main ()
{
  std::unordered_multimap<std::string,std::string> myumm = {
         {"strawberry","red"},
         {"banana","yellow"},
         {"orange","orange"},
         {"lemon","yellow"},
         {"apple","red"},
         {"apple","green"},
         {"pear","green"},
  };


  // erase examples:
  myumm.erase ( myumm.begin() );     // erasing by iterator
  myumm.erase ("apple");             // erasing by key (erases 2 elements)
  myumm.erase ( myumm.find("orange"), myumm.end() ); // erasing by range

  // show content:
  for ( auto& x: myumm )
    std::cout << x.first << ": " << x.second << std::endl;

  return 0;
}
可能的输出

banana: yellow
strawberry: red


复杂度

Average case: Linear in the number of elements removed (which is constant for versions (1) and (2)).
Worst case: Linear in the container size.

迭代器有效性

Only the iterators and references to the elements removed are invalidated.
The rest are unaffected.
The relative order of iteration of equivalent elements not removed by the operation is preserved.
The relative order of iteration of the elements not removed by the operation is preserved.

另见

unordered_multimap::clear
清除内容 (公开成员函数)
unordered_multimap::insert
插入元素 (公开成员函数)
unordered_multimap::find
获取指向元素的迭代器 (公共成员函数)