C++ map - max_size() Function

The C++ map::max_size function returns the maximum size the map can reach. The function returns the maximum potential size the map can reach due to known system or library implementation limitations.

Note: Map is an ordered data container which implies all its elements are ordered all the time.

Syntax

• C++98
• C++11

size_type max_size() const;

size_type max_size() const noexcept;

Parameters

No parameter is required.

Return Value

Maximum number of elements that can be held in a map.

Time Complexity

Constant i.e, Θ(1).

Example:

In the example below, the map::max_size function is used find out the maximum number of elements that a map can hold.

#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<<"The map contains:\n";
  for(it = MyMap.begin(); it != MyMap.end(); ++it)
     cout<<it->first<<"  "<<it->second<<"\n";

  cout<<"\nMap size is: "<<MyMap.size()<<"\n";
  cout<<"Maximum size of the Map: "<<MyMap.max_size()<<"\n"; 
  
  return 0;
}

A possible output could be:

The map contains:
101  John
102  Marry
103  Kim
104  Jo
105  Ramesh

Map size is: 5
Maximum size of the Map: 128102389400760775