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std::hash<std::filesystem::path>

From cppreference.com
< cpp‎ | filesystem‎ | path
 
 
 
 
Defined in header <filesystem>
template<>
struct hash<std::filesystem::path>;
(since C++17)

The template specialization of std::hash for std::filesystem::path allows users to obtain hash values of std::filesystem::path.

The operator() of this specialization is noexcept. For every std::filesystem::path value p, std::hash<std::filesystem::path>{}(p) is equal to std::filesystem::hash_value(p).

[edit] Example

#include <cassert>
#include <cstddef>
#include <iomanip>
#include <iostream>
#include <filesystem>
#include <unordered_set>
namespace fs = std::filesystem;
 
void show_hash(fs::path const& p)
{
    std::cout << std::hex << std::uppercase << std::setw(16)
              << std::hash<fs::path>{}(p) << " : " << p << '\n';
}
 
int main()
{
    auto tmp1 = fs::path{"/tmp"};
    auto tmp2 = fs::path{"/tmp/../tmp"};
    assert( ! (tmp1 == tmp2) );
    assert( fs::equivalent(tmp1, tmp2) );
    show_hash( tmp1 );
    show_hash( tmp2 );
 
    for (auto s : {"/a///b", "/a//b", "/a/c", "...", "..", ".", ""})
        show_hash(s);
 
    std::unordered_set<fs::path, std::hash<fs::path>> dirs {
        "/bin", "/bin", "/lib", "/lib", "/opt", "/opt", "/tmp", "/tmp/../tmp"
    };
    for (fs::path const& p: dirs) { std::cout << p << ' '; }
}

Possible output:

6050C47ADB62DFE5 : "/tmp"
62795A58B69AD90A : "/tmp/../tmp"
FF302110C9991974 : "/a///b"
FF302110C9991974 : "/a//b"
FD6167277915D464 : "/a/c"
C42040F82CD8B542 : "..."
D2D30154E0B78BBC : ".."
D18C722215ED0530 : "."
               0 : ""
"/tmp/../tmp" "/opt" "/lib" "/tmp" "/bin"

[edit] See also

(C++11)
hash function object
(class template) [edit]
calculates a hash value for a path object
(function) [edit]