std::filesystem::is_directory(3)

NAME
std::filesystem::is_directory - std::filesystem::is_directory

Synopsis
   Defined in header <filesystem>
   bool is_directory( std::filesystem::file_status s ) noexcept; (1) (since C++17)
   bool is_directory( const std::filesystem::path& p ); (2) (since C++17)
   bool is_directory( const std::filesystem::path& p, (3) (since C++17)
   std::error_code& ec ) noexcept;
   Checks if the given file status or path corresponds to a directory.
   1) Equivalent to s.type() == file_type::directory.
   2,3) Equivalent to is_directory(status(p)) or is_directory(status(p, ec)),
   respectively.

Parameters
   s - file status to check
   p - path to query
   ec - error code to modify in case of errors

Return value
   true if the file indicated by p or if the type indicated s refers to a directory,
   false otherwise. 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.

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_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_socket checks whether the argument refers to a named IPC socket
   (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 directory
   is_directory (public member function of std::filesystem::directory_entry)