如何使用来自< system_error>的system_category错误代码的通用错误代码枚举？ [英] How do I use the generic error codes enum with system_category error codes from <system_error>?

问题描述

我有这个代码（非常类似于这里有什么建议）引发异常：

I have this code (very similar to what is suggested here) that throws an exception:

int accept4(int sockfd, sockaddr *addr, socklen_t *addrlen, int flags)
{
   const int fd = ::accept4(sockfd, addr, addrlen, flags);
   if (fd < 0)
   {
       const auto tmp = errno;
       throw ::std::system_error(tmp, ::std::system_category(), "accept4(2)");
   }
   else
   {
      return fd;
   }
}

此代码用于测试特定异常原因：

And this code for testing for a particular exception reason:

catch (const ::std::system_error &e)
{
   static const auto block_err = ::std::system_error(EWOULDBLOCK,
                                                     ::std::system_category());

   const auto ecode = e.code(); 

   // EWOULBLOCK is fine, everything else, re-throw it.
   if (block_err.code() != ecode)
   {
      throw;
   }
}

这似乎是不必要的冗长，不是很正确做事情的方式有一般错误和整个枚举的全部想法（请参阅 ： ：std :: errc ），以及某些系统，应该在系统特定的错误代码和这些通用错误之间进行转换。

This seems kind of needlessly verbose and not quite the right way to do things. There's this whole idea of generic errors and a whole enum (see ::std::errc) full of them along with some kind of system that's supposed to convert between system specific error codes and these generic errors.

我想使用通用错误代码和类别，我似乎无法让他们工作。如何做这项工作？

I want to use the generic error codes and categories, and I can't seem to get them to work. How do I make that work?

推荐答案

在高质量 ^* 的实现中，足够了要执行

On an implementation of sufficiently high quality^*, it suffices to do

if (e.code() != std::errc::operation_would_block)
    throw;

如果没有，你被困在

if (e.code() != std::error_code(EWOULDBLOCK, std::system_category()))
    throw;

当然不需要构建另一个 system_error

There's certainly no need to construct another system_error just for the error code inside.

^* 需要实现 system_category（）的 default_error_condition 以将错误映射到 generic_category（）。

^* It needs to implement system_category()'s default_error_condition to appropriately map the error to generic_category().

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