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std::filesystem::directory_entry::is_block_file

来自 cppreference.com
 
C++
 
文件系统库
类
函数
文件类型
 
std::filesystem::directory_entry
成员函数
修改器
观察者
directory_entry::is_block_file
(直到 C++20)(直到 C++20)(直到 C++20)(直到 C++20)(直到 C++20)(C++20)
非成员函数
 
bool is_block_file() const;
 (1) (自 C++17 起)
bool is_block_file( std::error_code& ec ) const noexcept;
 (2) (自 C++17 起)

检查指向的对象是否为块设备。实际上返回

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

内容

[编辑] 参数

ec - 非抛出重载中用于错误报告的输出参数

[编辑] 返回值

true 如果引用的文件系统对象是块设备，否则为 false。

[编辑] 异常

任何未标记为 noexcept 的重载可能会在内存分配失败时抛出 std::bad_alloc。

1) 在底层 OS API 错误上抛出 std::filesystem::filesystem_error，使用 p 作为第一个路径参数，并使用 OS 错误代码作为错误代码参数进行构造。
2) 如果 OS API 调用失败，则将 std::error_code& 参数设置为 OS API 错误代码，如果未发生错误，则执行 ec.clear()。

[编辑] 示例

运行此代码
#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

可能的输出

"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")

[编辑] 另请参阅

(C++17)
 检查给定路径是否引用块设备
(函数) [编辑]
检索自 "https://cppreference.cn/mwiki/index.php?title=cpp/filesystem/directory_entry/is_block_file&oldid=158262"