std::errc

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std::errc
 
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在标头 <system_error> 定义
enum class errc;
 (C++11 起)
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有作用域枚举 std::errc 定义对应于 POSIX 错误码的可移植错误条件。

成员常量

名称 等价的 POSIX 错误
address_family_not_supported EAFNOSUPPORT
address_in_use EADDRINUSE
address_not_available EADDRNOTAVAIL
already_connected EISCONN
argument_list_too_long E2BIG
argument_out_of_domain EDOM
bad_address EFAULT
bad_file_descriptor EBADF
bad_message EBADMSG
broken_pipe EPIPE
connection_aborted ECONNABORTED
connection_already_in_progress EALREADY
connection_refused ECONNREFUSED
connection_reset ECONNRESET
cross_device_link EXDEV
destination_address_required EDESTADDRREQ
device_or_resource_busy EBUSY
directory_not_empty ENOTEMPTY
executable_format_error ENOEXEC
file_exists EEXIST
file_too_large EFBIG
filename_too_long ENAMETOOLONG
function_not_supported ENOSYS
host_unreachable EHOSTUNREACH
identifier_removed EIDRM
illegal_byte_sequence EILSEQ
inappropriate_io_control_operation ENOTTY
interrupted EINTR
invalid_argument EINVAL
invalid_seek ESPIPE
io_error EIO
is_a_directory EISDIR
message_size EMSGSIZE
network_down ENETDOWN
network_reset ENETRESET
network_unreachable ENETUNREACH
no_buffer_space ENOBUFS
no_child_process ECHILD
no_link ENOLINK
no_lock_available ENOLCK
no_message_available (弃用) ENODATA
no_message ENOMSG
no_protocol_option ENOPROTOOPT
no_space_on_device ENOSPC
no_stream_resources (弃用) ENOSR
no_such_device_or_address ENXIO
no_such_device ENODEV
no_such_file_or_directory ENOENT
no_such_process ESRCH
not_a_directory ENOTDIR
not_a_socket ENOTSOCK
not_a_stream (弃用) ENOSTR
not_connected ENOTCONN
not_enough_memory ENOMEM
not_supported ENOTSUP
operation_canceled ECANCELED
operation_in_progress EINPROGRESS
operation_not_permitted EPERM
operation_not_supported EOPNOTSUPP
operation_would_block EWOULDBLOCK
owner_dead EOWNERDEAD
permission_denied EACCES
protocol_error EPROTO
protocol_not_supported EPROTONOSUPPORT
read_only_file_system EROFS
resource_deadlock_would_occur EDEADLK
resource_unavailable_try_again EAGAIN
result_out_of_range ERANGE
state_not_recoverable ENOTRECOVERABLE
stream_timeout (弃用) ETIME
text_file_busy ETXTBSY
timed_out ETIMEDOUT
too_many_files_open_in_system ENFILE
too_many_files_open EMFILE
too_many_links EMLINK
too_many_symbolic_link_levels ELOOP
value_too_large EOVERFLOW
wrong_protocol_type EPROTOTYPE

非成员函数

(C++11)
 为 errc 枚举 e 创建错误码值
(函数) [编辑]
(C++11)
 为 errc 值 e 创建错误条件
(函数) [编辑]

辅助类

(C++11)
 扩充 std::is_error_condition_enum 类型特性，以鉴别 errc 值为某种错误条件
(函数模板) [编辑]

示例

运行此代码
#include <filesystem>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <string>
#include <system_error>
#include <thread>

void print_error(const std::string& details, std::error_code error_code)
{
    std::string value_name;
    if (error_code == std::errc::invalid_argument)
        value_name = "std::errc::invalid_argument";
    if (error_code == std::errc::no_such_file_or_directory)
        value_name = "std::errc::no_such_file_or_directory";
    if (error_code == std::errc::is_a_directory)
        value_name = "std::errc::is_a_directory";
    if (error_code == std::errc::permission_denied)
        value_name = "std::errc::permission_denied";

    std::cout << details << ":\n  "
              << std::quoted(error_code.message())
              << " (" << value_name << ")\n\n";
}

void print_errno(const std::string& details, int errno_value = errno)
{
    print_error(details, std::make_error_code(std::errc(errno_value)));
}

int main()
{
    std::cout << "脱离不是线程的线程...\n";
    try
    {
        std::thread().detach();
    }
    catch (const std::system_error& e)
    {
        print_error("脱离空线程时报错", e.code());
    }

    std::cout << "打开不存在的文件...\n";
    std::ifstream nofile{"nonexistent-file"};
    if (!nofile.is_open())
        print_errno("为读取打开不存在的文件时报错");

    std::cout << "将目录当作文件进行读取...\n";
    std::filesystem::create_directory("dir");
    std::ifstream dir_stream{"dir"};
    [[maybe_unused]] char c = dir_stream.get();
    if (!dir_stream.good())
        print_errno("从目录读取数据时报错");

    std::cout << "为写入打开只读文件...\n";
    std::fstream{"readonly-file", std::ios::out};
    std::filesystem::permissions("readonly-file", std::filesystem::perms::owner_read);
    std::fstream write_readonly("readonly-file", std::ios::out);
    if (!write_readonly.is_open())
        print_errno("为写入打开只读文件时报错");
}

可能的输出： 

脱离不是线程的线程...
脱离空线程时报错:
  "Invalid argument" (std::errc::invalid_argument)

打开不存在的文件...
为读取打开不存在的文件时报错:
  "No such file or directory" (std::errc::no_such_file_or_directory)

将目录当作文件进行读取...
从目录读取数据时报错:
  "Is a directory" (std::errc::is_a_directory)

为写入打开只读文件...
为写入打开只读文件时报错:
  "Permission denied" (std::errc::permission_denied)

缺陷报告

下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。

缺陷报告 应用于 出版时的行为 正确行为
LWG 3869 C++11 成员常量 no_message_available、no_stream_resources、
not_a_stream 和 stream_timeout 涉及了废弃的 POSIX STREAMS API[1] 		弃用这些成员常量
  1. ↑ 尽管对应的 POSIX 错误码 ENODATA、ENOSR、ENOSTR 和 ETIME 在 POSIX 2017 才被标为“即将废弃”，但以前的 POSIX 标准也不要求必须实现 STREAMS API（因为流行的类 Unix 系统拒绝实现它）。

参阅

(C++11)
 保有依赖于平台的错误码
(类) [编辑]
(C++11)
 保有可移植的错误码
(类) [编辑]