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

std::filesystem::is_block_file: std::filesystem::is_block_file

NAME

std::filesystem::is_block_file - std::filesystem::is_block_file

Synopsis

Defined in header <filesystem>
bool is_block_file( std::filesystem::file_status s ) noexcept; (1) (since C++17)
bool is_block_file( const std::filesystem::path& p ); (2) (since C++17)
bool is_block_file( const std::filesystem::path& p, std::error_code& ec ) noexcept;

Checks if the given file status or path corresponds to a block special file, as if determined by the POSIX S_ISBLK. Examples of block special files are block devices such as /dev/sda or /dev/loop0 on Linux.
1) Equivalent to s.type() == file_type::block.
2) Equivalent to is_block_file(status(p)) or is_block_file(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 block device. 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.

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