C ++使用cin.get获取字符，但遇到EOF时不结束while循环

Question

The following is my code, that I want to read characters from stdin, and end when it meet an EOF(ctrl-z).

#include<iostream>
#include<fstream>
#include<stdio.h>
#include<string>
using namespace std;

int main()
{
    string article ;    
    char nextChar;
    while( cin.get(nextChar) ) {
        if( cin.eof() ) break ;
        article.append(1, nextChar) ;
    }

    cout << article ;

    system("pause") ;
}

I test an input like this:

I am a student.<ctrl-z>

And then I press enter, but it does not halt.

When I type another [ctrl-z], and then press neter.

It just can exit from the while loop.

Why the first [ctrl-z] not to signal the eof condition?

Answer 1

The following explanation is slightly simplified.

It's a feature of your operating system. This is how your operating system works.

An end of file is, really, the underlying read() system call returning 0. An end of file is not CTRL-Z . CTRL-Z gets interpreted by your operating system to flush its interactive key buffer, and have the process read() its contents.

When you type in a terminal, the process does not actually end up reading anything until Enter is pressed. At that time the read() system call completes, and returns everything that's been read. In general, before pressing Enter you can backspace and edit what you typed, and your program has no indication that you've edited anything, all that it read ()s is the final contents of the line after pressing Enter .

If you type something, and press CTRL-Z , the typed input is also read () by the program as if it was typed in.

Only if nothing is typed, and CTRL-Z is pressed, does the underlying read() system call returns 0, because nothing got typed in first; this is interpreted as an end-of-file indication. But if something gets typed in first, CTRL-Z needs to be entered twice, once to read() the typed in input, and clear the input buffer, then CTRL-Z a second time, to cause an read () of 0.

By the way, your code has a harmless bug. If cin.get() succeeds, cin.eof() can never be true.