NAME¶

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

Synopsis¶

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

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) 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¶

1)
noexcept specification:
noexcept
2,3) The overload that does not take a 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 a 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

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.

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

Example¶

// Run this code

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

See also¶

status determines file attributes
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_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_symlink checks whether the argument refers to a symbolic link
(function)
exists checks whether path refers to existing file system object
(function)
cached status of the file designated by this directory entry
status cached symlink_status of the file designated by this directory
symlink_status entry
(public member function of
std::experimental::filesystem::directory_entry)