std::unordered_set max_size() method

since C++11

// Const version only
size_type max_size() const noexcept;

Returns the maximum number of elements the container is able to hold due to system or library implementation limitations, i.e. std::distance(begin(), end()) for the largest container.

Parameters

(none)

Return value

Maximum number of elements.

Complexity

Constant - O(1).

Exceptions

(none)

Notes

This value typically reflects the theoretical limit on the size of the container, at most std::numeric_limits<difference_type>::max(). At runtime, the size of the container may be limited to a value smaller than max_size() by the amount of RAM available.

Example

Main.cpp

#include <iostream>
#include <locale>
#include <unordered_set>
 
int main()
{
    std::unordered_set<char> q;
    std::cout.imbue(std::locale("en_US.UTF-8"));    
    std::cout << "Maximum size of a std::unordered_set is " << q.max_size() << '\n';
}

Possible output

Maximum size of a std::unordered_set is 768,614,336,404,564,650