std::hash(3)

NAME
std::hash - std::hash

Synopsis
   Defined in header <filesystem>
   template<> (since C++17)
   struct hash<std::filesystem::path>;
   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).
   This specialization was absent from the C++17 standard publication, see LWG issue
   3657.

Example
// Run this code
 #include <cassert>
 #include <cstddef>
 #include <filesystem>
 #include <iomanip>
 #include <iostream>
 #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 << ' ';
     std::cout << '\n';
 }

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"

See also
   hash hash function object
   (C++11) (class template)
   hash_value calculates a hash value for a path object
   (C++17) (function)