noskipws对cin的影响

问题描述

据我所知，提取操作符会跳过开头的空格，并在遇到空格或流结尾时停止.noskipws 可用于停止忽略前导空格.

As I understand, the extraction operator skips the whitespace in the beginning and stops upon encountering a whitespace or end of stream. noskipws can be used to stop ignoring the leading whitespaces.

我在以下程序中使用了 noskipws.

I have the following program where I have used noskipws.

#include <iostream>
using namespace std;

int main()
{
    char name[128];

    cout<<"Enter a name ";
    cin>>noskipws>>name;
    cout<<"You entered "<<name<<"
";

    cout<<"Enter another name ";
    cin>>name;
    cout<<"You entered "<<(int)name[0]<<"
";

    return 0;
}

我的查询是:

1. 如果我输入John"作为第一个输入，那么第二个 cin>> 操作不会等待输入并且不会将任何内容复制到目标，即名称数组.我希望第二个 cin>> 至少传输一个换行符或流的结尾，而不是仅仅将目标字符串设置为空.为什么会发生这种情况?

1. If I enter "John" as the first input, then the second cin>> operation does not wait for input and does not copy anything to the destination i.e. the name array. I expected second cin>> to transfer at-least a newline or end of stream, instead of just setting the destination string to empty. Why is this happening ?

当我输入John Smith"作为第一个 cin>> 语句的输入时，观察到同样的事情.为什么第二个 cin>> 语句不将空格或Smith"复制到目标变量?

The same thing is observed when I enter "John Smith" as the input for first cin>> statement. Why doesn't the second cin>> statement copy the space or "Smith" to the destination variable ?

以下是程序的输出:

Enter a name John
You entered John
Enter another name You entered 0


Enter a name John Smith
You entered John
Enter another name You entered 0

谢谢！！！

推荐答案

>> 字符串的基本算法是:

The basic algorithm for >> of a string is:

skip whitespace
read and extract until next whitespace

如果您使用noskipws，则跳过第一步.第一次读取后，您被定位在一个空白处，因此下一次(以及所有后续)读取将立即停止，不提取任何内容.

If you use noskipws, then the first step is skipped. After the first read, you are positionned on a whitespace, so the next (and all following) reads will stop immediatly, extracting nothing.

>> 到字符串永远不会将空格放入字符串中.更一般地，将 >> 与 noskipws 一起使用是有问题的，因为空格始终是 >>> 的分隔符；准时使用它可能是有意义的，但通常应该在使用后立即重置.(一次可能有意义的情况是将 >> 用于 char.在这种情况下，流 always 提取一个字符.)

>> to a string will never put whitespace into the string. More generally, using >> with noskipws is problematic, since whitespace is always a separator for >>; it may make sense to use it punctually, but it should generally be reset immediately after it has been used. (The once case where it might make sense is when using >> to a char. In this case, the stream always extracts one character.)

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