std::filesystem::equivalent

Defined in header `<filesystem>`
bool equivalent( const std::filesystem::path& p1, const std::filesystem::path& p2 ); bool equivalent( const std::filesystem::path& p1, const std::filesystem::path& p2, std::error_code& ec ) noexcept;		(since C++17)

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

The overload that does not take a std::error_code& parameter throws 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. The overload taking a std::error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur. Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

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 <iostream>
#include <cstdint>
#include <filesystem>
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

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External libraries

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