map::erase

项目
06/09/2015

从指定位置的映射中移除一个元素或一定范围内的元映或移除与指定关键值匹配的元素。

iterator erase(
   const_iterator Where
);

iterator erase(
   const_iterator First,
   const_iterator Last
);

size_type erase(
   const key_type& Key
);

参数

Where
要移除的元素的位置。
First
要移除的第一个元素的位置。
Last
最后一个元素前面的要移除元素的位置。
Key
要移除元素的关键值。

返回值

对于前两个成员函数，指定保持在所有元素外的第一个元素中移除一双向迭代器或如果不存在这样的元素设置为末尾的元素。

为第三个成员函数，返回从集合中移除元素的数目。

示例

// map_erase.cpp
// compile with: /EHsc
#include <map>
#include <string>
#include <iostream>
#include <iterator> // next() and prev() helper functions
#include <utility>  // make_pair()

using namespace std;

using mymap = map<int, string>;

void printmap(const mymap& m) {
    for (const auto& elem : m) {
        cout << " [" << elem.first << ", " << elem.second << "]";
    }
    cout << endl << "size() == " << m.size() << endl << endl;
}

int main()
{
    mymap m1;

    // Fill in some data to test with, one at a time
    m1.insert(make_pair(1, "A"));
    m1.insert(make_pair(2, "B"));
    m1.insert(make_pair(3, "C"));
    m1.insert(make_pair(4, "D"));
    m1.insert(make_pair(5, "E"));

    cout << "Starting data of map m1 is:" << endl;
    printmap(m1);
    // The 1st member function removes an element at a given position
    m1.erase(next(m1.begin()));
    cout << "After the 2nd element is deleted, the map m1 is:" << endl;
    printmap(m1);

    // Fill in some data to test with, one at a time, using an intializer list
    mymap m2
    {
        { 10, "Bob" },
        { 11, "Rob" },
        { 12, "Robert" },
        { 13, "Bert" },
        { 14, "Bobby" }
    };

    cout << "Starting data of map m2 is:" << endl;
    printmap(m2);
    // The 2nd member function removes elements
    // in the range [First, Last)
    m2.erase(next(m2.begin()), prev(m2.end()));
    cout << "After the middle elements are deleted, the map m2 is:" << endl;
    printmap(m2);

    mymap m3;

    // Fill in some data to test with, one at a time, using emplace
    m3.emplace(1, "red");
    m3.emplace(2, "yellow");
    m3.emplace(3, "blue");
    m3.emplace(4, "green");
    m3.emplace(5, "orange");
    m3.emplace(6, "purple");
    m3.emplace(7, "pink");

    cout << "Starting data of map m3 is:" << endl;
    printmap(m3);
    // The 3rd member function removes elements with a given Key
    mymap::size_type count = m3.erase(2);
    // The 3rd member function also returns the number of elements removed
    cout << "The number of elements removed from m3 is: " << count << "." << endl;
    cout << "After the element with a key of 2 is deleted, the map m3 is:" << endl;
    printmap(m3);
}

Output

Starting data of map m1 is:
 [1, A] [2, B] [3, C] [4, D] [5, E]
size() == 5

After the 2nd element is deleted, the map m1 is:
 [1, A] [3, C] [4, D] [5, E]
size() == 4

Starting data of map m2 is:
 [10, Bob] [11, Rob] [12, Robert] [13, Bert] [14, Bobby]
size() == 5

After the middle elements are deleted, the map m2 is:
 [10, Bob] [14, Bobby]
size() == 2

Starting data of map m3 is:
 [1, red] [2, yellow] [3, blue] [4, green] [5, orange] [6, purple] [7, pink]
size() == 7

The number of elements removed from m3 is: 1.
After the element with a key of 2 is deleted, the map m3 is:
 [1, red] [3, blue] [4, green] [5, orange] [6, purple] [7, pink]
size() == 6