std::filesy...aracter_file(3)

💅 character-device check, but make it filesystem ✨

okay so this is the std::filesy...aracter_file(3) page from the C++ Standard Libary — manual name exactly like that, typo and all, because that's what the header says 💀🫶. We're talking about std::filesystem::directory_entry::is_character_file, and it's lowkey iconic.

🌸 NAME 🌸

std::filesystem::directory_entry::is_character_file — and the NAME section says std::filesystem::directory_entry::is_character_file right back at you, so yes, the double-name repetition is canon 💖.

✨ Synopsis ✨

bool is_character_file() const;                               (1)
(since C++17)
bool is_character_file( std::error_code& ec ) const noexcept; (2)
(since C++17)

It checks whether the pointed-to object is a character device, periodt. Effectively it returns:

1. std::filesystem::is_character_file(status())
2. std::filesystem::is_character_file(status(ec))

🎀 Parameters 🎀

• ec — out-parameter for error reporting in the non-throwing overload. That's the whole parameter list, bestie.

💖 Return value 💖

true if the referred-to filesystem object is a character device, false otherwise. No cap.

😭 Exceptions 😭

Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails. Fr fr, that's the baseline.

1. 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. 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.

🧚 Example 🧚

This one is a whole demo, okay? Run this code:

// Run this code

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

namespace fs = std::filesystem;

void print_entry_type(const std::filesystem::directory_entry& entry)
{
    std::cout << entry.path() << ": ";

    if (!entry.exists())
        std::cout << "does not exist ";
    if (entry.is_block_file())
        std::cout << "is a block device ";
    if (entry.is_character_file())
        std::cout << "is a character device ";
    if (entry.is_directory())
        std::cout << "is a directory ";
    if (entry.is_fifo())
        std::cout << "is a named IPC pipe ";
    if (entry.is_regular_file())
        std::cout << "is a regular file ";
    if (entry.is_socket())
        std::cout << "is a named IPC socket ";
    if (entry.is_symlink())
        std::cout << "(a symlink)";
    if (entry.is_other())
        std::cout << "(an `other` file)";

    std::cout << '\n';
}

template<typename Type, typename Fun>
class scoped_cleanup
{
    std::unique_ptr<Type, std::function<void(const Type*)>> u;

public:
    scoped_cleanup(Type* ptr, Fun fun) : u{ptr, std::move(fun)} {}
};

int main()
{
    // Create files of different kinds.
    std::filesystem::current_path(fs::temp_directory_path());
    const std::filesystem::path sandbox{"sandbox"};
    scoped_cleanup remove_all_at_exit{&sandbox, [](const fs::path* p)
    {
        std::cout << "cleanup: remove_all(" << *p << ")\n";
        fs::remove_all(*p);
    }};
    std::filesystem::create_directory(sandbox);
    std::ofstream{sandbox/"file"}; // Creates a regular file
    std::filesystem::create_directory(sandbox/"dir");

    mkfifo((sandbox/"pipe").string().data(), 0644);
    struct sockaddr_un addr; addr.sun_family = AF_UNIX;

    std::strcpy(addr.sun_path, (sandbox/"sock").string().data());
    int fd{socket(PF_UNIX, SOCK_STREAM, 0)};
    scoped_cleanup close_socket_at_exit{&fd, [](const int* f)
    {
        std::cout << "cleanup: close socket #" << *f << '\n';
        close(*f);
    }};
    bind(fd, reinterpret_cast<sockaddr*>(std::addressof(addr)), sizeof
addr);

    fs::create_symlink("file", sandbox/"symlink");

    for (std::filesystem::directory_entry entry:
fs::directory_iterator(sandbox))
        print_entry_type(entry);

    // Request file system objects status directly:
    for (const char* str : {"/dev/null", "/dev/cpu",
"/usr/include/c++",
                            "/usr/include/asm", "/usr/include/time.h"})
        print_entry_type(fs::directory_entry{str});

} // Cleanup via scoped_cleanup objects

🌈 Possible output 🌈

"sandbox/symlink": is a regular file (a symlink)
"sandbox/sock": is a named IPC socket (an `other` file)
"sandbox/pipe": is a named IPC pipe (an `other` file)
"sandbox/dir": is a directory
"sandbox/file": is a regular file
"/dev/null": is a character device (an `other` file)
"/dev/cpu": does not exist
"/usr/include/c++": is a directory
"/usr/include/asm": is a directory (a symlink)
"/usr/include/time.h": is a regular file
cleanup: close socket #3
cleanup: remove_all("sandbox")

👀 See also 👀

• is_character_file checks whether the given path refers to a character device (C++17) (function)

mwah 💖 — source: http://cppreference.com; version/date: 2024.06.10; footer title: std::filesy...aracter_file(3).