std::filesystem::directory_entry::is_block_file

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C++
 
Filesystem library
Classes
Functions
File types
 
std::filesystem::directory_entry
Member functions
Modifiers
Observers
directory_entry::is_block_file
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Non-member functions
 
bool is_block_file() const;
 (1) (since C++17)
bool is_block_file( std::error_code& ec ) const noexcept;
 (2) (since C++17)

Checks whether the pointed-to object is a block device. Effectively returns:

1) std::filesystem::is_block_file(status()).
2) std::filesystem::is_block_file(status(ec)).

Parameters

ec - out-parameter for error reporting in the non-throwing overload

Return value

true if the referred-to filesystem object is a block device, false otherwise.

Exceptions

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

1) 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.
2) 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 <functional>
#include <iostream>
#include <memory>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <unistd.h>
 
namespace fs = std::filesystem;
 
void print_entry_type(const std::filesystem::directory_entry& entry)
{
    std::cout << entry.path() << ": ";
 
    if (!entry.exists())
        std::cout << "does not exist ";
    if (entry.is_block_file())
        std::cout << "is a block device ";
    if (entry.is_character_file())
        std::cout << "is a character device ";
    if (entry.is_directory())
        std::cout << "is a directory ";
    if (entry.is_fifo())
        std::cout << "is a named IPC pipe ";
    if (entry.is_regular_file())
        std::cout << "is a regular file ";
    if (entry.is_socket())
        std::cout << "is a named IPC socket ";
    if (entry.is_symlink())
        std::cout << "(a symlink)";
    if (entry.is_other())
        std::cout << "(an `other` file)";
 
    std::cout << '\n';
}
 
template<typename Type, typename Fun>
class scoped_cleanup
{
    std::unique_ptr<Type, std::function<void(const Type*)>> u;
 
public:
    scoped_cleanup(Type* ptr, Fun fun) : u{ptr, std::move(fun)} {}
};
 
int main()
{
    // Create files of different kinds.
    std::filesystem::current_path(fs::temp_directory_path());
    const std::filesystem::path sandbox{"sandbox"};
    scoped_cleanup remove_all_at_exit{&sandbox, [](const fs::path* p)
    {
        std::cout << "cleanup: remove_all(" << *p << ")\n";
        fs::remove_all(*p);
    }};
    std::filesystem::create_directory(sandbox);
    std::ofstream{sandbox/"file"}; // Creates a regular file
    std::filesystem::create_directory(sandbox/"dir");
 
    mkfifo((sandbox/"pipe").string().data(), 0644);
    struct sockaddr_un addr; addr.sun_family = AF_UNIX;
 
    std::strcpy(addr.sun_path, (sandbox/"sock").string().data());
    int fd{socket(PF_UNIX, SOCK_STREAM, 0)};
    scoped_cleanup close_socket_at_exit{&fd, [](const int* f)
    {
        std::cout << "cleanup: close socket #" << *f << '\n';
        close(*f);
    }};
    bind(fd, reinterpret_cast<sockaddr*>(std::addressof(addr)), sizeof addr);
 
    fs::create_symlink("file", sandbox/"symlink");
 
    for (std::filesystem::directory_entry entry: fs::directory_iterator(sandbox))
        print_entry_type(entry);
 
    // Request file system objects status directly:
    for (const char* str : {"/dev/null", "/dev/cpu", "/usr/include/c++",
                            "/usr/include/asm", "/usr/include/time.h"})
        print_entry_type(fs::directory_entry{str});
 
} // Cleanup via scoped_cleanup objects

Possible output: 

"sandbox/symlink": is a regular file (a symlink) 
"sandbox/sock": is a named IPC socket (an `other` file) 
"sandbox/pipe": is a named IPC pipe (an `other` file) 
"sandbox/dir": is a directory 
"sandbox/file": is a regular file 
"/dev/null": is a character device (an `other` file) 
"/dev/cpu": does not exist 
"/usr/include/c++": is a directory 
"/usr/include/asm": is a directory (a symlink) 
"/usr/include/time.h": is a regular file 
cleanup: close socket #3
cleanup: remove_all("sandbox")

See also

(C++17)
 checks whether the given path refers to block device
(function)
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