vector max_size() function in C++ STL

The vector::max_size() is a built-in function in C++ STL which returns the maximum number of elements that can be held by the vector container. 

Syntax:

vector_name.max_size()

Parameters: The function does not accept any parameters. 

Return value: The function returns the maximum numbers that can fit into the vector container. 

Time Complexity – Constant O(1) 

Program below illustrates the above function: 

CPP

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

int main()
{
    // initialize a vector
    vector<int> vec;

    // returns the max_size of vector
    cout << "max_size of vector 1 = " << vec.max_size() << endl;

    vector<int> vec1;

    // returns the max_size of vector
    cout << "max_size of vector 2 = " << vec1.max_size() << endl;
    return 0;
}

Output:

max_size of vector 1 = 4611686018427387903
max_size of vector 2 = 4611686018427387903