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std::hash(3)		       C++ Standard Libary		    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 al-
     lows 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)

http://cppreference.com 	   2024.06.10			    std::hash(3)
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