如何使用< system_error>将errno转换为异常 [英] How to convert errno to exception using <system_error>

问题描述

我阅读了周到的关于C ++ 11中的新的< system_error> 标题的一系列博客文章。它表示头部定义了代表操作返回的特定错误值（例如系统调用）的 error_code 类。它表示标题定义了一个 system_error 类，它是一个异常类（继承自 runtime_exception ），用于包裹 error_codes s。

I read a thoughtful series of blog posts about the new <system_error> header in C++11. It says that the header defines an error_code class that represents a specific error value returned by an operation (such as a system call). It says that the header defines a system_error class, which is an exception class (inherits from runtime_exception) and is used to wrap error_codess.

我想知道的是如何将系统错误从 errno 到一个 system_error ，所以我可以把它。例如，POSIX 打开函数通过返回-1并设置 errno 来报告错误，所以如果我想抛出例外我应该如何完成下面的代码？

What I want to know is how to actually convert a system error from errno into a system_error so I can throw it. For example, the POSIX open function reports errors by returning -1 and setting errno, so if I want to throw an exception how should I complete the code below?

void x()
{
    fd = open("foo", O_RDWR);
    if (fd == -1)
    {
        throw /* need some code here to make a std::system_error from errno */;
    }
}

我随机尝试：

errno = ENOENT;
throw std::system_error();

但是，当 what（）被调用。

我知道我可以做 throw errno; 但是我想这样做方式，使用新的< system_error> 头。

I know I could do throw errno; but I want to do it the right way, using the new <system_error> header.

有一个 system_error 将单个 error_code 作为参数，所以如果我可以只转换 errno 到 error_code 然后其他应该是显而易见的。

There is a constructor for system_error that takes a single error_code as its argument, so if I can just convert errno to error_code then the rest should be obvious.

这似乎是一个非常基本的事情，所以我不知道为什么我找不到一个很好的教程。

This seems like a really basic thing, so I don't know why I can't find a good tutorial on it.

我在ARM处理器上使用gcc 4.4.5，如果这很重要。

I am using gcc 4.4.5 on an ARM processor, if that matters.

推荐答案

你在正确的轨道上，只传递错误代码和一个 std :: system_category 对象 std :: system_error 构造函数，它应该可以工作：

You are on the right track, just pass the error code and a std::system_category object to the std::system_error constructor and it should work:

示例：

#include <iostream>
#include <system_error>

int main()
{
    try
    {
        throw std::system_error(EFAULT, std::system_category());
    }
    catch (std::system_error& error)
    {
        std::cout << "Error: " << error.code() << " - " << error.what() << '\n';
    }
}

我系统上面的程序的输出是

Output from the above program on my system is

Error: system:14 - Bad address

这篇关于如何使用< system_error>将errno转换为异常的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！