c++ - 使用 mingw 编译 websocketpp 示例代码时未定义对 `std::errc::operation_canceled` 的引用

Question

我正在尝试使用 websocketpp编写一个使用 websockets 进行通信的跨平台程序。我想使用 asio基于传输层。

我的理解是，如果我使用 C++11，我可以配置 asio独立于提升并使用std::thread ，那websocketpp在这种情况下类似地仅 header 。

但是，当我实际尝试编译 websocketpp 中的任何一个时这样的教程，比如 tutorials/utility_client ，它在 g++ 和 clang 上工作正常，但我在 mingw 上遇到奇怪的编译错误:

In file included from websocketpp-0.6.0/include/websocketpp/config/asio_no_tls_client.hpp:32:0,
                 from main.cpp:7:
websocketpp-0.6.0/include/websocketpp/transport/asio/endpoint.hpp: In member function ‘void websocketpp::transport::asio::endpoint<config>::handle_accept(websocketpp::transport::accept_handler, const error_code&)’:
websocketpp-0.6.0/include/websocketpp/transport/asio/endpoint.hpp:764:28: error: ‘operation_canceled’ is not a member of ‘std::errc’
             if (asio_ec == lib::asio::errc::operation_canceled) {
                            ^

我绞尽脑汁想知道这意味着什么以及如何解决这个问题。这似乎与缺乏提升无关——std::errc::operation_canceled根据 this, not always accurate, website 似乎是一个明确定义的 C++11 符号.这是否意味着我的工具链损坏/有缺陷？我尝试安装不同版本的 mingw 工具链，但它遇到了同样的问题。

我找不到任何对没有找到此符号有类似问题的人的引用，所以也许我配置库有误？这是我的编译行:

"$CXX" -std=c++11 -Iasio-1.10.6/include -Iwebsocketpp-0.6.0/include -D_WEBSOCKETPP_CPP11_THREAD_=1 -DASIO_STANDALONE=1 main.cpp -lpthread

I made a repository以协助重现我的确切设置，但这里没有太多进展——我从各自的 repo 协议(protocol)中下载了最新版本的两个库。由于编译死于其中一个包含 main.cpp 的正文似乎不是很相关，但我只是在使用他们的教程代码。

如果有人能就此给我留言，我将不胜感激。 :)

编辑:我不太确定，但我已将此报告为 mingw-w64 上的错误: http://sourceforge.net/p/mingw-w64/support-requests/105/

Answer 1

I have reported this as a bug at mingw-w64

mingw-w64 编译器在未定义此错误代码方面不符合 C++11，但人们已经知道了，这是故意的。 (虽然副手我不知道他们为什么不能修复它。)

相关的头文件是:

<toochain_dir>/mingw64/x86_64-w64-mingw32/include/c++/x86_64-w64-mingw32/bits/error_constants.h

这里是 enum class std::errc 的定义:

// Most of the commented-out error codes are socket-related and could be
// replaced by Winsock WSA-prefixed equivalents.
  enum class errc
    {
//    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,
#ifdef _GLIBCXX_HAVE_ECHILD
      no_child_process =            ECHILD,
#endif
//    no_link =                 ENOLINK,
      no_lock_available =           ENOLCK,
//    no_message_available =            ENODATA,
//    no_message =              ENOMSG,
//    no_protocol_option =          ENOPROTOOPT,
#ifdef _GLIBCXX_HAVE_ENOSPC
      no_space_on_device =          ENOSPC,
#endif
//    no_stream_resources =             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 =                ENOSTR,
//    not_connected =               ENOTCONN,
      not_enough_memory =           ENOMEM,
#ifdef _GLIBCXX_HAVE_ENOTSUP
      not_supported =               ENOTSUP,
#endif
//    operation_canceled =          ECANCELED,
//    operation_in_progress =           EINPROGRESS,
#ifdef _GLIBCXX_HAVE_EPERM
      operation_not_permitted =         EPERM,
#endif
//    operation_not_supported =         EOPNOTSUPP,
#ifdef _GLIBCXX_HAVE_EWOULDBLOCK
      operation_would_block =           EWOULDBLOCK,
#endif
//    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 =              ETIME,
//    text_file_busy =              ETXTBSY,
#ifdef _GLIBCXX_HAVE_ETIMEDOUT
      timed_out =               ETIMEDOUT,
#endif
      too_many_files_open_in_system =       ENFILE,
      too_many_files_open =             EMFILE,
      too_many_links =              EMLINK
//    too_many_symbolic_link_levels =       ELOOP,
#ifdef _GLIBCXX_HAVE_EOVERFLOW
    ,
      value_too_large =             EOVERFLOW
#endif
//    wrong_protocol_type =             EPROTOTYPE
   };

您看到 operation_canceled 是其中一个被注释掉的。

按照那里的建议，您将需要使用 winsock 错误代码 WSAECANCELLED，在 winerror.h 中定义。如果你想要便携性，当然你需要以主机操作系统的编译时确定为条件，而不是使用 std::errc::operation_canceled。