C++ map - clear() Function

The C++ map::clear function is used to clear all elements of the map. This function makes the map empty with a size of zero.

Syntax

C++98
C++11

void clear();

void clear() noexcept;

Parameters

No parameter is required.

Return Value

None.

Time Complexity

Linear i.e, Θ(n)

Example:

In the example below, the map::clear function is used to clear all elements of the map called MyMap.

#include <iostream>
#include <map>
using namespace std;
 
int main (){
  map<int, string> MyMap;
  map<int, string>::iterator it;

  MyMap[101] = "John";
  MyMap[102] = "Marry";
  MyMap[103] = "Kim";
  MyMap[104] = "Jo";
  MyMap[105] = "Ramesh";

  cout<<"Before clear() function: \nMyMap contains:\n";
  for(it = MyMap.begin(); it != MyMap.end(); ++it)
    cout<<it->first<<" "<<it->second<<"\n";
  cout<<"\nMyMap size is: "<<MyMap.size()<<"\n\n";

  MyMap.clear();

  cout<<"After clear() function: \nMyMap contains:\n";
  for(it = MyMap.begin(); it != MyMap.end(); ++it)
    cout<<it->first<<" "<<it->second<<"\n";
  cout<<"MyMap size is: "<<MyMap.size();

  return 0;
}

The output of the above code will be:

Before clear() function: 
MyMap contains:
101 John
102 Marry
103 Kim
104 Jo
105 Ramesh

MyMap size is: 5

After clear() function: 
MyMap contains:
MyMap size is: 0

❮ C++ <map> Library