std::experi...racter_file(3)

🦋 NAME 🦋

Bestie, welcome to the C++ Standard Library manual (section 3, she's fancy 💅). Today's main character:

std::experimental::filesystem::is_character_file — std::experimental::filesystem::is_character_file

Yes, they wrote it twice. No notes. 🎀

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✨ SYNOPSIS ✨

Okay so this whole thing lives in the <experimental/filesystem> header:

Defined in header <experimental/filesystem>
bool is_character_file( file_status s );                 (1)
(filesystem TS)
bool is_character_file( const path& p );                 (2)
(filesystem TS)
bool is_character_file( const path& p, error_code& ec );

What's the vibe? It checks if a given file status or path corresponds to a character special file, as if determined by POSIX S_ISCHR. Character special files are character devices — think /dev/null, /dev/tty, /dev/audio, or /dev/nvram on Linux. 🐚

1. Equivalent to s.type() == file_type::character.
2. Equivalent to is_character_file(status(p)) or is_character_file(status(p, ec)), respectively.

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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, false otherwise. The non-throwing overload returns false if an error occurs.

🤨 And yes, the page really does say "block device" in the return value section of is_character_file. I'm quoting, not editorialising. I am simply the messenger, bestie. 🙈

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🔥 EXCEPTIONS 🔥

1. noexcept specification:

noexcept

2. The overload that does not take an error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first argument and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. The overload taking an 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. This overload has noexcept specification:

noexcept

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🌸 NOTES 🌸

The info this function gives you is usually also provided as a byproduct of directory iteration. So during directory iteration, calling is_character_file(*iterator) is less efficient than is_character_file(iterator->status()) — like, why redo the work when the answer's already right there? Efficiency queen behavior only 👑.

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🌈 EXAMPLE 🌈

// Run this code

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

namespace fs = std::experimental::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");
    std::ofstream("sandbox/file"); // create regular file
    fs::create_directory("sandbox/dir");
    mkfifo("sandbox/pipe", 0644);
    struct 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, (struct sockaddr*)&addr, sizeof addr);
    fs::create_symlink("file", "sandbox/symlink");

    // 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
    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

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🧚 SEE ALSO 🧚

• status — determines file attributes (function)
• symlink_status — determines file attributes, checking the symlink target (function)
• file_status — represents file type and permissions (class)
• status_known — checks whether file status is known (function)
• is_block_file — checks whether the given path refers to block device (function)
• is_directory — checks whether the given path refers to a directory (function)
• is_fifo — checks whether the given path refers to a named pipe (function)
• is_other — checks whether the argument refers to an other file (function)
• is_regular_file — checks whether the argument refers to a regular file (function)
• is_socket — checks whether the argument refers to a named IPC socket (function)
• is_symlink — checks whether the argument refers to a symbolic link (function)
• exists — checks whether path refers to existing file system object (function)
• status — cached status of the file designated by this directory entry
• symlink_status — cached symlink_status of the file designated by this directory entry

(those last two are a public member function of std::experimental::filesystem::directory_entry, iykyk 🫶)

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🎀 CATEGORIES 🎀

• Noindexed pages
• unconditionally noexcept

💀 Hidden categories 💀

• Pages with unreviewed unconditional noexcept template
• Pages with unreviewed noexcept template

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And that's the page, bestie! Source is cppreference.com, dated 2024.06.10, and the whole thing answers to std::experi...racter_file(3) in the C++ Standard Library manual. Slay, go check your /dev/null 💖✨🦋