# std::filesystem::is_socket

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< cpp‎ | filesystem

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 ); bool is_socket( const std::filesystem::path& p, std::error_code& ec ) noexcept; | (2) | (since C++17)

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

2) The overload that does not take a std::error_code& parameter throws `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. The overload taking a std::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. Any overload not marked `noexcept` may throw std::bad_alloc if memory allocation fails.

### 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 <iostream>
    #include <fstream>
    #include <cstdio>
    #include <cstring>
    #include <filesystem>
    #include <unistd.h>
    #include <sys/socket.h>
    #include <sys/un.h>
    #include <sys/stat.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");
        std::ofstream("sandbox/file"); // create regular file
        fs::create_directory("sandbox/dir");
        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);
        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 symlink_status (C++17)(C++17) | determines file attributes determines file attributes, checking the symlink target (function)
file_status (C++17) | represents file type and permissions (class)
status_known (C++17) | checks whether file status is known (function)
is_block_file (C++17) | checks whether the given path refers to block device (function)
is_character_file (C++17) | checks whether the given path refers to a character device (function)
is_directory (C++17) | checks whether the given path refers to a directory (function)
is_fifo (C++17) | checks whether the given path refers to a named pipe (function)
is_other (C++17) | checks whether the argument refers to an other file (function)
is_regular_file (C++17) | checks whether the argument refers to a regular file (function)
is_symlink (C++17) | checks whether the argument refers to a symbolic link (function)
exists (C++17) | checks whether path refers to existing file system object (function)
is_socket | checks whether the directory entry refers to a named IPC socket (public member function of `std::filesystem::directory_entry`)

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