std::hashstd::filesystem::path - cppreference.com (original) (raw)

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

#include #include #include #include #include #include namespace fs = std::filesystem;   void show_hash(fs::path const& p) { std::cout << std::hex << std::uppercase << std::setw(16) << std::hashfs::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::hashfs::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"

[edit] See also

| | hash function object (class template) [edit] | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | calculates a hash value for a path object (function) [edit] |