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std::filesy...::hash_value(3)  C++ Standard Libary std::filesy...::hash_value(3)

NAME
     std::filesystem::hash_value - std::filesystem::hash_value

Synopsis
	Defined in header <filesystem>
	std::size_t  hash_value(  const  std::filesystem::path&  p  )  noexcept;
     (since C++17)

Parameters
	p - a std::filesystem::path object

Return value
	A hash value such that if for two paths, p1 == p2 then hash_value(p1) ==
	hash_value(p2).

	The return value is consistent with std::hash.

Notes
	Equality of two paths is determined by comparing  each	component  sepa-
     rately, so, for
	example "a//b" equals "a/b" and has the same hash_value.

	hash_value  originates	from  the  Boost.filesystem library where it was
     used for
	interoperability with boost.hash (which calls hash_value found by  argu-
     ment-dependent
	lookup or boost::hash_value where available).

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)
		    << fs::hash_value(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);

	  // A hash function object to work with unordered_* containers:
	  struct PathHash
	  {
	      std::size_t operator()(fs::path const& p) const noexcept
	      {
		  return fs::hash_value(p);
	      }
	  };
	  std::unordered_set<fs::path, PathHash> 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
					 compares the lexical representations of
     two paths
	compare 			 lexicographically
					 (public member function)
	operator==
	operator!=
	operator<
	operator<=
	operator>
	operator>=
	operator<=>			 lexicographically compares two paths
	(C++17) 			 (function)
	(C++17)(until C++20)
	(C++17)(until C++20)
	(C++17)(until C++20)
	(C++17)(until C++20)
	(C++17)(until C++20)
	(C++20)
	equivalent			 checks whether two paths refer  to  the
     same file
	(C++17) 			 system object
					 (function)
	hash				 hash function object
	(C++11) 			 (class template)
	std::hash<std::filesystem::path> hash support for std::filesystem::path
	(C++17) 			 (class template specialization)

http://cppreference.com 	   2024.06.10	   std::filesy...::hash_value(3)
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