std::hash<std::filesystem::path>
From cppreference.com
< cpp | filesystem | path
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
std::filesystem::path
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
hash<std::filesystem::path>
(C++26)
Defined in header
<filesystem>
template<>
struct hash<std::filesystem::path >;
(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.
[edit] 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"