std::hash<std::filesystem::path>

 

C++

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Feature test macros(C++20)

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Concepts library(C++20)

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Metaprogramming library(C++11)

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Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Filesystem library

Classes
filesystem::path filesystem::filesystem_error filesystem::directory_entry filesystem::directory_iterator filesystem::recursive_directory_iterator    filesystem::file_status filesystem::space_info	filesystem::file_type filesystem::file_time_type filesystem::perms filesystem::perm_options filesystem::copy_options filesystem::directory_options
Functions
filesystem::absolute filesystem::canonicalfilesystem::weakly_canonical filesystem::relativefilesystem::proximate filesystem::copy filesystem::copy_file filesystem::copy_symlink filesystem::create_directory filesystem::create_directories filesystem::create_hard_link filesystem::create_symlink filesystem::create_directory_symlink filesystem::current_path filesystem::temp_directory_path	filesystem::exists filesystem::equivalent filesystem::file_size filesystem::hard_link_count filesystem::last_write_time filesystem::permissions filesystem::read_symlink filesystem::remove filesystem::remove_all filesystem::rename filesystem::resize_file filesystem::space filesystem::status filesystem::symlink_status
File types
filesystem::is_block_file filesystem::is_character_file filesystem::is_directory filesystem::is_empty filesystem::status_known	filesystem::is_fifo filesystem::is_other filesystem::is_regular_file filesystem::is_socket filesystem::is_symlink

 

std::filesystem::path

Member types
Member constants
path::native_formatpath::generic_formatpath::auto_format
Member functions
path::path path::~path path::operator= path::assign path::appendpath::operator/= path::concatpath::operator+= path::clear path::make_preferred path::remove_filename path::replace_filename path::replace_extension    path::swap path::compare path::beginpath::end	path::c_strpath::nativepath::operator string_type path::stringpath::u8stringpath::u16stringpath::u32stringpath::wstring path::generic_stringpath::generic_u8stringpath::generic_u16stringpath::generic_u32stringpath::generic_wstring path::lexically_normalpath::lexically_relativepath::lexically_proximate
Path decomposition
path::root_name path::root_directory path::root_path path::relative_path path::parent_path path::filename path::stem path::extension path::empty	path::has_root_pathpath::has_root_namepath::has_root_directorypath::has_relative_pathpath::has_parent_pathpath::has_filenamepath::has_stempath::has_extension path::is_absolutepath::is_relative
Non-member functions
operator==operator!=operator<operator<=operator>operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)	operator/ operator<<operator>> swap(std::filesystem::path) hash_value u8path
Helper classes
hash<std::filesystem::path>	formatter<std::filesystem::path> (C++26)

 

Defined in header <filesystem>
template<> struct hash<std::filesystem::path>;		(since C++17)

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.

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::pathconst& 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::pathconst& 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 (C++11)	hash function object (class template)
hash_value (C++17)	calculates a hash value for a path object (function)