std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::max_bucket_count

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C++
 
Containers library
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(C++11)
(C++11)
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Unordered associative
(C++11)
(C++11)
(C++11)
(C++11)
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(C++20)
 
std::unordered_map
Member functions
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(C++17)
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Bucket interface
unordered_map::max_bucket_count
Hash policy
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Non-member functions
(until C++20)
(C++20)
Deduction guides(C++17)
 
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

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