std::filesy...mlink_status(3)

🎀 NAME 🎀

okay so bestie, this is the std::filesy...mlink_status(3) page from the C++ Standard Libary (yes, that spelling is in the header — iconic, we keep it 💅). It's all about std::filesystem::directory_entry::status and std::filesystem::directory_entry::symlink_status.

The NAME line literally says: std::filesystem::directory_entry::status,std::filesystem::directory_entry::symlink_status - std::filesystem::directory_entry::status,std::filesystem::directory_entry::symlink_status. Yes it repeats itself, no cap, and we're not erasing that.

✨ Synopsis ✨

Here's the exact signature lineup, with the (since C++17) tags and all:

std::filesystem::file_status status() const;
(1) (since C++17)
std::filesystem::file_status status( std::error_code& ec ) const
(2) (since C++17)
noexcept;
std::filesystem::file_status symlink_status() const;
(3) (since C++17)
std::filesystem::file_status symlink_status( std::error_code& ec )
(4) (since C++17)
const noexcept;

Then:

• 1,2) Returns status of the entry, as if determined by a filesystem::status call (symlinks are followed to their targets).
• 3,4) Returns status of the entry, as if determined by a filesystem::symlink_status call (symlinks are not followed).

💖 Parameters 💖

• ec — out-parameter for error reporting in the non-throwing overload.

🌸 Return value 🌸

The status of the file referred to by the entry. That's the whole vibe. 🫶

🔥 Exceptions 🔥

• Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.
• 1,3) Throws std::filesystem::filesystem_error on underlying OS API errors, constructed with p as the first path argument and the OS error code as the error code argument.
• 2,4) 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 🦋

Many low-level OS APIs for directory traversal retrieve file attributes along with the next directory entry. The constructors and the non-const member functions of std::filesystem::directory_iterator store these attributes, if any, in the pointed-to std::filesystem::directory_entry without calling directory_entry::refresh, which makes it possible to examine the attributes of the directory entries as they are being iterated over, without making additional system calls. ngl that's kind of a slay — cached attributes, no extra syscalls. ✨

💅 Example 💅

// Run this code

        #include <cstdio>
        #include <cstring>
        #include <filesystem>
        #include <fstream>
        #include <iostream>
        #include <sys/socket.h>
        #include <sys/stat.h>
        #include <sys/un.h>
        #include <unistd.h>

        namespace fs = std::filesystem;

        void demo_status(const fs::path& p, fs::file_status s)
        {
            std::cout << p;
            // alternative: switch(s.type()) { case fs::file_type::regular:
       ...}
            if (fs::is_regular_file(s))
                std::cout << " is a regular file\n";
            if (fs::is_directory(s))
                std::cout << " is a directory\n";
            if (fs::is_block_file(s))
                std::cout << " is a block device\n";
            if (fs::is_character_file(s))
                std::cout << " is a character device\n";
            if (fs::is_fifo(s))
                std::cout << " is a named IPC pipe\n";
            if (fs::is_socket(s))
                std::cout << " is a named IPC socket\n";
            if (fs::is_symlink(s))
                std::cout << " is a symlink\n";
            if (!fs::exists(s))
                std::cout << " does not exist\n";
        }

        int main()
        {
            // create files of different kinds
            fs::create_directory("sandbox");
            fs::create_directory("sandbox/dir");
            std::ofstream{"sandbox/file"}; // create regular file
            fs::create_symlink("file", "sandbox/symlink");

            mkfifo("sandbox/pipe", 0644);
            sockaddr_un addr;
            addr.sun_family = AF_UNIX;
            std::strcpy(addr.sun_path, "sandbox/sock");
            int fd = socket(PF_UNIX, SOCK_STREAM, 0);
            bind(fd, reinterpret_cast<sockaddr*>(&addr), sizeof addr);

            // demo different status accessors
            for (auto it{fs::directory_iterator("sandbox")}; it !=
       fs::directory_iterator(); ++it)
                demo_status(*it, it->symlink_status()); // use cached status
       from directory entry
            demo_status("/dev/null", fs::status("/dev/null")); // direct calls
       to status
            demo_status("/dev/sda", fs::status("/dev/sda"));
            demo_status("sandbox/no", fs::status("/sandbox/no"));

            // cleanup (prefer std::unique_ptr-based custom deleters)
            close(fd);
            fs::remove_all("sandbox");
        }

🍓 Possible output 🍓

"sandbox/file" is a regular file
"sandbox/dir" is a directory
"sandbox/pipe" is a named IPC pipe
"sandbox/sock" is a named IPC socket
"sandbox/symlink" is a symlink
"/dev/null" is a character device
"/dev/sda" is a block device
"sandbox/no" does not exist

🌈 See also 🌈

• refresh — updates the cached file attributes (public member function)
• exists — checks whether directory entry refers to existing file system object (public member function)
• is_block_file — checks whether the directory entry refers to block device (public member function)
• is_character_file — checks whether the directory entry refers to a character device (public member function)
• is_directory — checks whether the directory entry refers to a directory (public member function)
• is_fifo — checks whether the directory entry refers to a named pipe (public member function)
• is_other — checks whether the directory entry refers to an other file (public member function)
• is_regular_file — checks whether the directory entry refers to a regular file (public member function)
• is_socket — checks whether the directory entry refers to a named IPC socket (public member function)
• is_symlink — checks whether the directory entry refers to a symbolic link (public member function)
• file_size — returns the size of the file to which the directory entry refers (public member function)
• hard_link_count — returns the number of hard links referring to the file to which the directory entry refers (public member function)
• last_write_time — gets the time of the last data modification of the file to which the directory entry refers (public member function)

source + version + date check, as promised: this page comes from http://cppreference.com, dated 2024.06.10, and it's the std::filesy...mlink_status(3) page. byeee bestie, go check those symlink statuses responsibly 💖🦋