Difference between revisions of "cpp/filesystem/equivalent"

Revision as of 12:02, 26 November 2016

Checks whether the paths p1 and p2 refer to the same file or directory and have the same file status as determined by status (symlinks are followed).

If neither p1 nor p2 exists, or if both exist but neither is a file, directory, or symlink (as determined by is_other), an error is reported.

The non-throwing overload returns false on errors.

Parameters

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.
The overload that does not take a std::error_code& parameter 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. 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.

Notes

Two paths are considered to resolve to the same file system entity if st_dev and st_ino of their POSIX stat structure, obtained as if by POSIX stat, are equal. (meaning, the files are locate on the same device at the same location)

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

#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
    fs::path p3 = "/lib/libc.so.6";
    fs::path p4 = p3.parent_path() / fs::read_symlink(p3);
    if(fs::equivalent(p3, p4))
        std::cout << p3 << " is equivalent to " << p4 << '\n';
}

"." is equivalent to "/var/tmp/test"
"/lib/libc.so.6" is equivalent to "/lib/libc-2.12.so"

See also