std::unordered_map::max_bucket_count(3)

NAME
std::unordered_map::max_bucket_count - std::unordered_map::max_bucket_count

Synopsis
   size_type max_bucket_count() const; (since C++11)
   Returns the maximum number of buckets the container is able to hold due to system or
   library implementation limitations.

Parameters
   (none)

Return value
   Maximum number of buckets.

Complexity
   Constant.

Example
// Run this code
 #include <iostream>
 #include <unordered_map>
 int main()
 {
     struct Ha { std::size_t operator()(long x) const { return std::hash<long>{}(x); }; };
     auto c1 = std::unordered_map<char, long>{};
     auto c2 = std::unordered_map<long, long>{};
     auto c3 = std::unordered_map<long, long, std::hash<int>>{};
     auto c4 = std::unordered_map<long, long, Ha>{};
     std::cout
         << "Max bucket count of\n" << std::hex << std::showbase
         << "c1: " << c1.max_bucket_count() << '\n'
         << "c2: " << c2.max_bucket_count() << '\n'
         << "c3: " << c3.max_bucket_count() << '\n'
         << "c4: " << c4.max_bucket_count() << '\n'
         ;
 }

Possible output:
 Max bucket count of
 c1: 0xfffffffffffffff
 c2: 0xfffffffffffffff
 c3: 0xfffffffffffffff
 c4: 0xaaaaaaaaaaaaaaa

See also
   bucket_count returns the number of buckets
   (C++11) (public member function)