NAME¶

std::filesystem::is_socket - std::filesystem::is_socket

Synopsis¶

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

Checks if the given file status or path corresponds to a named IPC socket, as if
determined by the POSIX S_IFSOCK.

1) Equivalent to s.type() == file_type::socket.
2,3) Equivalent to is_socket(status(p)) or is_socket(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 named socket.
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.

Notes¶

Named sockets are UNIX domain sockets constructed with socket and bind POSIX APIs,
which may be used for advanced interprocess communication. In particular, they may
be used to transport open file descriptors from one running process to another.

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_block_file checks whether the given path refers to block device
(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_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 a named IPC socket
is_socket (public member function of std::filesystem::directory_entry)