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map::clear() in C++ STL

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Map is dictionary like data structure. It is an associative array of (key, value) pair, where only single value is associated with each unique key. map::clear() clear() function is used to remove all the elements from the map container and thus leaving it’s size 0. Syntax:
map1.clear()
where map1 is the name of the map.

Parameters:
No parameters are passed.
Return Value: None Examples:
Input : map1 = { 
                {1, "India"},
                {2, "Nepal"},
                {3, "Sri Lanka"},
                {4, "Myanmar"}
               }
        map1.clear();
Output: map1 = {}

Input : map2 = {}
        map2.clear();
Output: map2 = {}
// CPP program to illustrate
// Implementation of clear() function
#include <bits/stdc++.h>
using namespace std;
  
int main()
{
    // Take any two maps
    map<int, string> map1, map2;
      
    // Inserting values
    map1[1] = "India";
    map1[2] = "Nepal";
    map1[3] = "Sri Lanka";
    map1[4] = "Myanmar";
      
    // Print the size of map
    cout<< "Map size before running function: \n";
    cout << "map1 size = " << map1.size() << endl;
    cout << "map2 size = " << map2.size() << endl;;
      
    // Deleting the map elements
    map1.clear();
    map2.clear();
      
    // Print the size of map
    cout<< "Map size after running function: \n";
    cout << "map1 size = " << map1.size() << endl;
    cout << "map2 size = " << map2.size();
    return 0;
}

                    
Output:
Map size before running function: 
map1 size = 4
map2 size = 0
Map size after running function: 
map1 size = 0
map2 size = 0
Time complexity: Linear i.e. O(n)

Last Updated : 20 Jan, 2018
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