std::filesystem::equivalent(3)

NAME
std::filesystem::equivalent - std::filesystem::equivalent

Synopsis
   Defined in header <filesystem>
   bool equivalent( const std::filesystem::path& p1, (1) (since C++17)
                    const std::filesystem::path& p2 );
   bool equivalent( const std::filesystem::path& p1,
                    const std::filesystem::path& p2, (2) (since C++17)
                    std::error_code& ec ) noexcept;
   Checks whether the paths p1 and p2 resolve to the same file system entity.
   If either p1 or p2 does not exist, an error is reported.
   The non-throwing overload returns false on errors.

Parameters
   p1, p2 - paths to check for equivalence
   ec - out-parameter for error reporting in the non-throwing overload

Return value
   true if the p1 and p2 refer to the same file or directory and their file status is
   the same. false otherwise.

Exceptions
   Any overload not marked noexcept may throw std::bad_alloc if memory allocation
   fails.
   1) Throws std::filesystem::filesystem_error on underlying OS API errors, constructed
   with p1 as the first path argument, p2 as the second path argument, and the OS error
   code as the error code argument.
   2) Sets a std::error_code& parameter to the OS API error code if an OS API call
   fails, and executes ec.clear() if no errors occur.

Notes
   Two paths are considered to resolve to the same file system entity if the two
   candidate entities the paths resolve to are located on the same device at the same
   location. For POSIX, this means that the st_dev and st_ino members of their POSIX
   stat structure, obtained as if by POSIX stat(), are equal.
   In particular, all hard links for the same file or directory are equivalent, and a
   symlink and its target on the same file system are equivalent.

Example
// Run this code
 #include <cstdint>
 #include <filesystem>
 #include <iostream>
 namespace fs = std::filesystem;
 int main()
 {
     // hard link equivalency
     fs::path p1 = ".";
     fs::path p2 = fs::current_path();
     if (fs::equivalent(p1, p2))
         std::cout << p1 << " is equivalent to " << p2 << '\n';
     // symlink equivalency
     for (const fs::path lib : {"/lib/libc.so.6", "/lib/x86_64-linux-gnu/libc.so.6"})
     {
         try
         {
             p2 = lib.parent_path() / fs::read_symlink(lib);
         }
         catch (std::filesystem::filesystem_error const& ex)
         {
             std::cout << ex.what() << '\n';
             continue;
         }
         if (fs::equivalent(lib, p2))
             std::cout << lib << " is equivalent to " << p2 << '\n';
     }
 }

Possible output:
 "." is equivalent to "/var/tmp/test"
 filesystem error: read_symlink: No such file or directory [/lib/libc.so.6]
 "/lib/x86_64-linux-gnu/libc.so.6" is equivalent to "/lib/x86_64-linux-gnu/libc-2.23.so"
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 2937 C++17 error condition specified incorrectly corrected

See also
                        compares the lexical representations of two paths
   compare lexicographically
                        (public member function of std::filesystem::path)
   operator==
   operator!=
   operator<
   operator<=
   operator>
   operator>=
   operator<=> lexicographically compares two paths
   (C++17) (function)
   (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)
   status determines file attributes
   symlink_status determines file attributes, checking the symlink target
   (C++17) (function)
   (C++17)