std::experi..._block_file(3)

💅 NAME 💅

std::experimental::filesystem::is_block_file — std::experimental::filesystem::is_block_file. Bestie, welcome to the std::experi..._block_file(3) page from the C++ Standard Libary manual. This is the little function that checks if a file status or path is a block special file. That’s the name section, periodt.

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✨ Synopsis ✨

Defined in header <experimental/filesystem>

bool is_block_file( file_status s );                          (1)
(filesystem TS)
bool is_block_file( const path& p );                          (2)
(filesystem TS)
bool is_block_file( const path& p, error_code& ec ) noexcept;

It 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.

• 1) Equivalent to s.type() == file_type::block.
• 2) 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 by s refers to a block device. The non-throwing overload returns false if an error occurs.

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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 information provided by this function is usually also provided as a byproduct of directory iteration. During directory iteration, calling is_block_file(*iterator) is less efficient than is_block_file(iterator->status()).

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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");
}

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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 (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_character_file — checks whether the given path refers to a character 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 (public member function of std::experimental::filesystem::directory_entry)

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🎀 Categories 🎀

• Noindexed pages
• unconditionally noexcept

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🙈 Hidden categories 🙈

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

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💖 That’s the whole page, bestie. Source/version: http://cppreference.com; date: 2024.06.10; page: std::experi..._block_file(3). Go check your block devices and slay. 🎀