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std::filesy...::hash_value(3) C++ Standard Libarystd::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 sep-
       arately,	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
       argument-dependent
	  lookup or boost::hash_value where available).

Example
       // Run this code

	#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)
		      << 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 << '	'; }
	}

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  representa-
       tions of	two paths
	  compare			   lexicographically
					   (public member function)
	  operator==
	  operator!=
	  operator<
	  operator<=
	  operator>
	  operator>=			    lexicographically	compares   two
       paths
	  operator<=>			   (function)
	  (until C++20)
	  (until C++20)
	  (until C++20)
	  (until C++20)
	  (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::filesys-
       tem::path
	  (C++17)			   (class template specialization)

http://cppreference.com		  2022.07.31	 std::filesy...::hash_value(3)

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