重置流的状态 [英] Resetting the State of a Stream

问题描述

我有一个问题，在这个问题上稍微类似于stackoverflow std :: cin.clear（）无法恢复良好状态的输入流，但是提供的答案不适用于我。

I have a question which is slightly similar to this question on stackoverflow std::cin.clear() fails to restore input stream in a good state, but the answer provided there does not work for me.

问题是：如何重置一个流的状态为好？

The question is: how can I reset the state of a stream to 'good' again?

这是我的代码如何尝试，从来没有设置好。

Here is my code how I try it, but the state is never set to good again. I used both of the lines ignore separately.

int _tmain(int argc, _TCHAR* argv[])
{
    int result;
    while ( std::cin.good() )
    {
        std::cout << "Choose a number: ";
        std::cin >> result;

        // Check if input is valid
        if (std::cin.bad())
        {
            throw std::runtime_error("IO stream corrupted");
        }
        else if (std::cin.fail())
        {
            std::cerr << "Invalid input: input must be a number." << std::endl;
            std::cin.clear(std::istream::failbit);
            std::cin.ignore();
            std::cin.ignore(INT_MAX,'\n');
            continue;
        }
        else
        {
            std::cout << "You input the number: " << result << std::endl;
        }
    }
    return 0;
}

推荐答案

>

The code here

std::cin.clear(std::istream::failbit);

实际上不会清除失败位，它会取代当前状态

doesn't actually clear the failbit, it replaces the current state of the stream with failbit.

要清除所有位，只需调用 clear 。

To clear all the bits, just call clear().

标准中的描述是一个复杂的，函数

The description in the standard is a but convoluted, stated as the result of other functions

void clear（iostate state = goodbit）;

后置条件：如果 rdbuf（）！= 0 then state == rdstate （）; 否则 rdstate（）==（state | ios_base :: badbit）。

Postcondition: If rdbuf()!=0 then state == rdstate(); otherwise rdstate()==(state | ios_base::badbit).

这基本上意味着下一次调用 rdstate（）将返回传递给 clear（） 。除了有其他一些问题，在这种情况下你也可能得到一个 badbit 。

Which basically means that the next call to rdstate() will return the value passed to clear(). Except when there are some other problems, in which case you might get a badbit as well.

清除<

cin.clear(cin.rdstate() & ~ios::failbit);

但是，如果清除一个标志，而其他标志仍保留，您仍然无法从流中读取。所以这种使用是相当有限的。

However, if you clear one flag and others remain, you still cannot read from the stream. So this use is rather limited.

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