NAME¶

std::filesystem::is_block_file - std::filesystem::is_block_file

Synopsis¶

Defined in header <filesystem>
bool is_block_file( std::filesystem::file_status s ) noexcept; (1) (since C++17)
bool is_block_file( const std::filesystem::path& p ); (2) (since C++17)
bool is_block_file( const std::filesystem::path& p, (3) (since C++17)
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.

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

Parameters¶

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

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.

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.

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¶

status determines file attributes
symlink_status determines file attributes, checking the symlink target
(C++17) (function)
(C++17)
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 argument 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)
checks whether the directory entry refers to block device
is_block_file (public member function of std::filesystem::directory_entry)