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)