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Difference between revisions of "cpp/filesystem/is socket"

From cppreference.com
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Revision as of 11:49, 19 April 2017

 
C++
 
Filesystem library
Classes
Functions
File types
 
Defined in header <filesystem>
bool is_socket( std::filesystem::file_status s );
 (1) (since C++17)
bool is_socket( const std::filesystem::path& p );
bool is_socket( const std::filesystem::path& p, std::error_code& ec );
 (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)).

Contents

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) Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

The overload that does not take a std::error_code& parameter throws std::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.

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

(C++17)(C++17)
 determines file attributes
determines file attributes, checking the symlink target
(function) [edit]
(C++17)
 represents file type and permissions
(class) [edit]
(C++17)
 checks whether file status is known
(function) [edit]
(C++17)
 checks whether the given path refers to block device
(function) [edit]
(C++17)
 checks whether the given path refers to a character device
(function) [edit]
(C++17)
 checks whether the given path refers to a directory
(function) [edit]
(C++17)
 checks whether the given path refers to a named pipe
(function) [edit]
(C++17)
 checks whether the argument refers to an other file
(function) [edit]
(C++17)
 checks whether the argument refers to a regular file
(function) [edit]
(C++17)
 checks whether the argument refers to a symbolic link
(function) [edit]
(C++17)
 checks whether path refers to existing file system object
(function) [edit]
checks whether the directory entry refers to a named IPC socket
(public member function of std::filesystem::directory_entry) [edit]
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