C++

参考

<unordered_map>

unordered_map

public member function
<unordered_map>

std::unordered_map::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_map container either a single element or a range of elements ([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_map.
成员类型const_iterator是一个 forward iterator 类型。
k
Key of the element to be erased.
成员类型key_type是容器中元素的键的类型，在 unordered_map 中定义为其第一个模板参数的别名（键).
first, last
Iterators specifying a range within the unordered_map 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_map 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, which in unordered_map containers (that have unique keys), this is1if an element with a key value of k existed (and thus was subsequently erased), and zero otherwise.

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_map::erase
#include <iostream>
#include <string>
#include <unordered_map>

int main ()
{
  std::unordered_map<std::string,std::string> mymap;

  // populating container:
  mymap["U.S."] = "Washington";
  mymap["U.K."] = "London";
  mymap["France"] = "Paris";
  mymap["Russia"] = "Moscow";
  mymap["China"] = "Beijing";
  mymap["Germany"] = "Berlin";
  mymap["Japan"] = "Tokyo";

  // erase examples:
  mymap.erase ( mymap.begin() );      // erasing by iterator
  mymap.erase ("France");             // erasing by key
  mymap.erase ( mymap.find("China"), mymap.end() ); // erasing by range

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

  return 0;
}
可能的输出
Russia: Moscow
Japan: Tokyo
U.K.: London


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

另见

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