std::filesy..._block_file(3)

🦋 NAME 🦋

std::filesystem::is_block_file — okay so the NAME is literally std::filesystem::is_block_file - std::filesystem::is_block_file, because she said it twice and honestly? iconic. This is the C++ Standard Libary manual page std::filesy..._block_file(3), and it’s all about checking block special files. Yes, “Libary” is the manual name — we don’t fix lore here 💀.

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✨ Synopsis ✨

Defined in header <filesystem>:

• (1) (since C++17) — bool is_block_file( std::filesystem::file_status s ) noexcept;
• (2) (since C++17) — bool is_block_file( const std::filesystem::path& p );
• (3) (since C++17) — bool is_block_file( const std::filesystem::path& p, std::error_code& ec ) noexcept;

Checks if the given file status or path corresponds to a block special file, as if determined by the POSIX S_ISBLK. Examples of block special files are block devices such as /dev/sda or /dev/loop0 on Linux. Slay, block devices. 💅

• 1) — Equivalent to s.type() == file_type::block.
• 2,3) — Equivalent to is_block_file(status(p)) or is_block_file(status(p, ec)).

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💖 Parameters 💖

• s — file status to check
• p — path to examine
• ec — out-parameter for error reporting in the non-throwing overload

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🌸 Return value 🌸

true if the file indicated by p or if the type indicated s refers to a block device. The non-throwing overload returns false if an error occurs.

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🎀 Exceptions 🎀

Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

2,3) 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.

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🧚 Example 🧚

Run this code, bestie — it’s giving “demo all the file types” energy:

#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");
}

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🌈 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

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👑 See also 👑

• status — determines file attributes — (C++17) (function)
• symlink_status — determines file attributes, checking the symlink target — (C++17) (function)
• file_status — represents file type and permissions — (C++17) (class)
• status_known — checks whether file status is known — (C++17) (function)
• is_character_file — checks whether the given path refers to a character device — (C++17) (function)
• is_directory — checks whether the given path refers to a directory — (C++17) (function)
• is_fifo — checks whether the given path refers to a named pipe — (C++17) (function)
• is_other — checks whether the argument refers to an other file — (C++17) (function)
• is_regular_file — checks whether the argument refers to a regular file — (C++17) (function)
• is_socket — checks whether the given path refers to a named IPC socket — (C++17) (function)
• is_symlink — checks whether the argument refers to a symbolic link — (C++17) (function)
• exists — checks whether path refers to existing file system object — (C++17) (function)
• is_block_file — checks whether the directory entry refers to block device — (public member function of std::filesystem::directory_entry)

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Source/version/date, so you can cite it in the group chat: http://cppreference.com, 2024.06.10, std::filesy..._block_file(3). That’s the whole page — go be a main character with your block devices 🫶💖