c++ - 多次从 std::cin 读取——Linux 和 Mac OS X 上的不同行为

Question

我想从标准输入中读取一些数字，处理它们，然后读取下一组数字。

我想到了读取 EOF 中的 char 字符并清除 eofbit、failbit 和 badbit 的解决方案。以下代码适用于带有 GCC 4.9.2 的 Ubuntu 14.04:

#include <iostream>
#include <vector>

int main() {
    std::vector<double> a;
    std::vector<double>::iterator it;
    double x;
    while(std::cin >> x) {
        a.push_back(x);
    }
    std::cout << "First bunch of numbers:" << std::endl;
    for (it = a.begin(); it != a.end(); ++it) {
        std::cout << *it << std::endl;
    }

    // get crap out of buffer
    char s;
    std::cin >> s;
    std::cin.clear();

    // go for it again
    while (std::cin >> x) {
        a.push_back(x);
    }
    std::cout << "All the numbers:" << std::endl;
    for (it = a.begin(); it != a.end(); ++it) {
        std::cout << *it << std::endl;
    }

    return 0;
}

所以，在 Ubuntu 上，我可以输入 1<Return>2<Return>^D ，得到一些输出，输入 3<Return>4<Return>^D ，得到更多输出，然后程序终止。

在 Mac OS 10.10 但是，使用相同的 GCC 版本，程序不会接受第二轮输入，而是在命中 ^D 后两次输出第一个数字序列第一次。

• 为什么会出现不一致的行为？是否可以解决它？
• 接受两次输入的惯用方法是什么？
• 在我的用例中，第一组数字最终可能会从文件或管道中读取。在那种情况下，我如何以交互方式请求额外的输入。

Answer 1

我不是很熟悉，但是这个人有一个类似的问题:Signal EOF in mac osx terminal

By default, OS X (formerly Mac OS X) terminals recognize EOF when control-D is pressed at the beginning of a line.

In detail, the actual operation is that, when control-D is pressed, all bytes in the terminal’s input buffer are sent to the running process using the terminal. At the start of a line, no bytes are in the buffer, so the process is told there are zero bytes available, and this acts as an EOF indicator.

This procedure doubles as a method of delivering input to the process before the end of a line: The user may type some characters and press control-D, and the characters will be sent to the process immediately, without the usual wait for enter/return to be pressed. After this “send all buffered bytes immediately” operation is performed, no bytes are left in the buffer. So, when control-D is pressed a second time, it is the same as the beginning of a line (no bytes are sent, and the process is given zero bytes), and it acts like an EOF.

You can learn more about terminal behavior by using the command “man 4 tty” in Terminal. The default line discipline is termios. You can learn more about the termios line discipline by using the command “man termios”.

Eric Postpischil 接受的答案

我没有 OSX 来测试，但也许这可以解释行为