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map::erase

Removes an element or a range of elements in a map from specified positions or removes elements that match a specified key.

iterator erase(
   const_iterator Where
);

iterator erase(
   const_iterator First,
   const_iterator Last
);

size_type erase(
   const key_type& Key
);

Parameters

  • Where
    Position of the element to be removed.

  • First
    Position of the first element to be removed.

  • Last
    Position just beyond the last element to be removed.

  • Key
    The key value of the elements to be removed.

Return Value

For the first two member functions, a bidirectional iterator that designates the first element remaining beyond any elements removed, or an element that is the end of the map if no such element exists.

For the third member function, returns the number of elements that have been removed from the map.

Example

// 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

Requirements

Header: <map>

Namespace: std

See Also

Reference

<map>

map Class

map::clear

map::max_size, map::clear, map::erase, and map::size

Standard Template Library