NAME¶

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

Synopsis¶

bool is_block_file() const; (since C++17)
bool is_block_file( std::error_code& ec ) const noexcept;

Checks whether the pointed-to object is a block device. Effectively returns
std::filesystem::is_block_file(status()) or
std::filesystem::is_block_file(status(ec)), respectively.

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¶

The overload that does not take a std::error_code& parameter throws
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. Any overload not marked
noexcept may throw std::bad_alloc if memory allocation fails.

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(std::filesystem::directory_entry const& 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);
}

// direct calls to status:
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¶

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