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C++ multimap::max_size() Function

The C++ std::multimap::max_size() function is used to returns the maximum number of elements a multimap container can hold based on available memory. It depends on the system and compiler implementation. It provides an upper limit for the containers capacity, allowing to manage memory efficiently and avoid potential overflow issues. The time complexity of this function is constant i.e. O(1).

Following is the syntax for std::multimap::max_size() function.

size_type max_size() const noexcept;

It does not accept any parameter.

This function returns the maximum numbers of elements a multimap can hold.

Let's look at the following example, where we are going to demonstrate the usage of max_size() function.

#include <iostream>
#include <map>
int main()
{
    std::multimap<int, char> a;
    std::cout << "Max_size of current multimap : " << a.max_size() << std::endl;
    return 0;
}

Following is the output of the above code −

Max_size of current multimap : 230584300921369395

Consider the following example, where we are going to get the current size and max_sixe of the multimap.

#include <iostream>
#include <map>
int main()
{
    std::multimap<int, char> a;
    a.insert({1, 'A'});
    a.insert({2, 'B'});
    std::cout << "Current_size : " << a.size() << std::endl;
    std::cout << "Max_size : " << a.max_size() << std::endl;
    return 0;
}

Output of the above code is as follows −

Current_size : 2
Max_size : 230584300921369395

In the following example, we are going to check whether is multimap is empty or not.

#include <iostream>
#include <map>
int main()
{
    std::multimap<int, std::string> a;
    if (a.max_size() == 0) {
        std::cout << "It cannot hold any elements." << std::endl;
    } else {
        std::cout << "It can hold elements." << std::endl;
    }
    return 0;
}

If we run the above code it will generate the following output −

It can hold elements.

multimap.htm

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