unordered_map max_size in C++ STL

The unordered_map::max_size is a built in function in C++ STL. It returns maximum number of elements which unordered_map can hold. Maximum number of elements in any container depends upon system and library implementation.
Syntax

size unordered_map.max_size()

Parameters: It does not accept any parameters.

Return type: Unsigned integer a container can hold maximum elements.

Example 1

// C++ program to illustrate the
// unordered_map::max_size function
#include <bits/stdc++.h>
using namespace std;

int main()
{

    // declaration of unordered_map
    unordered_map<int, int> sample;

    cout << " Current size is :  " << sample.size() << endl;
    cout << " max size is : " << sample.max_size() << endl;

    // insert elements
    sample.insert({ 1, 10 });
    sample.insert({ 2, 10 });
    sample.insert({ 3, 10 });
    sample.insert({ 4, 10 });

    cout << " Current size is :  " << sample.size() << endl;
    cout << " max size is : " << sample.max_size() << endl;

    return 0;
}

Output:

Current size is :  0
 max size is : 1152921504606846975
 Current size is :  4
 max size is : 1152921504606846975

Example 2

// C++ program to illustrate the
// unordered_map::max_size function
#include <bits/stdc++.h>
using namespace std;

int main()
{

    // declaration of unordered_map
    unordered_map<char, int> sample;

    cout << " Current size is :  " << sample.size() << endl;
    cout << " max size is : " << sample.max_size() << endl;

    // insert elements
    sample.insert({ 'a', 10 });
    sample.insert({ 'b', 10 });
    sample.insert({ 'c', 10 });

    cout << " Current size is :  " << sample.size() << endl;
    cout << " max size is : " << sample.max_size() << endl;

    return 0;
}

Output:

Current size is :  0
 max size is : 1152921504606846975
 Current size is :  3
 max size is : 1152921504606846975

Complexity : Its complexity is constant.