std::filesystem::is_socket (3) - Linux Manuals

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

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& 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) 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_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);
      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