std::hash(std::vector<bool>)

 

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std::vector<bool>

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eraseerase_if (C++20)(C++20)

operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

Helper classes

std::hash (C++11)

Deduction guides(C++17)

 

Defined in header <vector>
template< class Allocator > struct hash<std::vector<bool, Allocator>>;		(since C++11)

The template specialization of std::hash for std::vector<bool> allows users to obtain hashes of objects of type std::vector<bool>.

Example

Run this code

#include <iostream>
#include <unordered_set>
#include <vector>
 
using vb = std::vector<bool>;
 
vb to_vector_bool(unsigned n)
{
    vb v;
    do
    {
        v.push_back(n & 1);
        n >>= 1;
    }
    while(n);
    return v;
}
 
auto print(const vb& v, bool new_line = true)
{
    for (std::cout << "{ "; const bool e : v)
        std::cout << e << ' ';
    std::cout << '}' << (new_line ? '\n' : ' ');
}
 
int main()
{
    for (auto i{0U}; i != 8; ++i)
    {
        std::cout << std::hex << std::uppercase;
        vb v = to_vector_bool(i);
        std::cout << std::hash<vb>{}(v) << ' ' << std::dec;
        print(v);
    }
 
    // std::hash for vector<bool> makes it possible to keep them in
    // unordered_* associative containers, such as unordered_set.
 
    std::unordered_set v{ vb{0}, vb{0, 0}, vb{1}, vb{1}, vb{1, 0}, vb{1, 1} };
 
    for (vb const& e : v)
        print(e, 0);
}

Possible output:

6D09EE26D5863619 { 0 }
3C27D9F591D20E49 { 1 }
E74D3F72B7599C63 { 0 1 }
EE3BE81F55123770 { 1 1 }
3AAD2A2EDBEC6C35 { 0 0 1 }
EB057F773CB64C43 { 1 0 1 }
6E1354730102BE00 { 0 1 1 }
E2E622597C18899D { 1 1 1 }
{ 1 1 } { 1 0 } { 1 } { 0 0 } { 0 }

See also

hash (C++11)

hash function object (class template)