istream_iterator 在读取字符时忽略 EOF (Ctrl+D)

发布于 2024-12-03 13:21:53 字数 1033 浏览 1 评论 0原文

我正在尝试使用 istream_iterator 从 cin 读取字符。我读到按 Ctrl+D 会发送一个 EOF 字符来结束输入流。不幸的是，它出了点问题。这是我的代码：

#include <iterator>
int main()
{
  using namespace std;

  istream_iterator<char> it(cin), eos;
  while (it != eos) clog << *(it++);
}

我正在运行它并输入：as df，然后按Ctrl+D。它仅输出 asd 而没有最后一个 f，然后挂起等待输入。当我输入 gh 并再次按 Ctrl+D 时，它最后会打印剩余的 f 和 < code>g 来自下一个输入，但同样没有最后一个 h。当我最终按下 Ctrl+D 而不输入任何内容时，它会打印剩余的 h 并退出。

我希望它读取 asdf 并退出，因为我已经在第一个序列末尾按下了 Ctrl+D 。

为什么获取EOF后还在等待输入？
为什么它不打印 EOF 之前读取的最后一个字符？
为什么只有当我按 Ctrl+D 且之前没有输入任何内容时它才会退出？
这个循环需要如何改变才能使其按照我期望的方式运行？（即在输入中获取 Ctrl+D 序列后立即停止阅读，无论我之前是否输入过任何内容，并向上读取所有个字符到EOF）。

原文

I'm trying to use istream_iterator for reading characters from cin. I've read that pressing Ctrl+D sends an EOF character which ends the input stream. Unfortunately, something is going wrong with it. Here's my code:

#include <iterator>
int main()
{
  using namespace std;

  istream_iterator<char> it(cin), eos;
  while (it != eos) clog << *(it++);
}

I'm running it and typing: as df, then pressing Ctrl+D.
It outputs only asd without the last f and then hangs waiting for input. When I type gh and press Ctrl+D again, it prints the remaining f at last, and the g from next input, but again without the last h. And when I finally press Ctrl+D without typing anything, it prints the remaining h and exits.

I expected it to read asdf and exit, since I already pressed Ctrl+D at the end of this first sequence.

Why is it still waiting for input after getting EOF?
Why it doesn't print the last character read before EOF?
And why it exits only when I press Ctrl+D without typing anything before?
How does this loop need to change to make it behave in the way I expect? (i.e. stop reading immediately after getting Ctrl+D sequence in the input, no matter I typed anything before or not, and reading all characters up to the EOF).

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好多鱼好多余 2024-12-10 13:21:53

输入迭代器需要特别小心。以这种方式重写循环，其行为将变得与任何其他字符输入循环类似：

while (it != eos)
{
    clog << *it;
    it++;
}

这将解决“为什么它不打印最后一个字符”

PS：至于行中间的 EOF，它是 < a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap11.html#tag_11_01_09" rel="nofollow">POSIX 强制行为：

收到后，所有等待读取的字节立即传递给进程，无需等待换行符，并且 EOF 被丢弃。因此，如果没有字节等待（即 EOF 发生在行的开头），则 read() 应返回字节计数为零，表示文件结束指示。

Input iterators require special care. Rewrite your loop this way and the behavior will become similar to any other character input loop:

while (it != eos)
{
    clog << *it;
    it++;
}

That will take care of "Why it doesn't print the last character"

PS: as for EOF in the middle of the line, it is the POSIX-mandated behavior:

When received, all the bytes waiting to be read are immediately passed to the process without waiting for a newline, and the EOF is discarded. Thus, if there are no bytes waiting (that is, the EOF occurred at the beginning of a line), a byte count of zero shall be returned from the read(), representing an end-of-file indication.

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