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Defined in header <filesystem> | ||
std::size_t hash_value(conststd::filesystem::path& p)noexcept; | (since C++17) | |
Contents |
| p | - | astd::filesystem::path object |
A hash value such that if for two paths,p1== p2 thenhash_value(p1)== hash_value(p2).
The return value is consistent withstd::hash.
Equality of two paths is determined by comparing each component separately, so, for example"a//b" equals"a/b" and has the samehash_value.
hash_value originates from theBoost.filesystem library where it was used for interoperability with boost.hash (which callshash_value found byargument-dependent lookup orboost::hash_value where available).
#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)<< 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::pathconst& p)constnoexcept{return fs::hash_value(p);}};std::unordered_set<fs::path, PathHash> 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"
| compares the lexical representations of two paths lexicographically (public member function)[edit] | |
(C++17)(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) | lexicographically compares two paths (function)[edit] |
(C++17) | checks whether two paths refer to the same file system object (function)[edit] |
(C++11) | hash function object (class template)[edit] |
| hash support forstd::filesystem::path (class template specialization)[edit] |
