noskipws对cin>的影响> [英] Effect of noskipws on cin>>
问题描述
根据我的理解，提取操作符在开始时跳过空格，并在遇到空格或字符串结尾时停止。 noskipws可以用来停止忽略前面的空格。
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.
我有以下程序，我使用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<<"\n";
cout<<"Enter another name ";
cin>>name;
cout<<"You entered "<<(int)name[0]<<"\n";
return 0;
}
我的查询是：
-
如果我输入John作为第一个输入，则第二个cin >>操作不等待输入，也不会将任何东西复制到目标，即名称数组。我期望第二个cin >>到至少一个换行或流结束，而不只是设置目标字符串为空。为什么会发生这种情况？
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，观察到同样的情况。为什么第二个cin >>语句不会将空格或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
>
推荐答案
字符串>> 的基本算法是： p>
The basic algorithm for >> of a string is:
skip whitespace
read and extract until next whitespace
如果使用 noskipws ，则跳过第一步。第一次读取后，您位于空白处，因此下一个（以及所有后续的）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.
;> 到字符串将永远不会将空格放入字符串。更一般地，使用>> 与 noskipws 有问题，因为空格总是>> ;它可能有意义的使用它准时，但它通常应该在使用后立即重置。 （在使用>> 到 char 时可能有意义的一次性情况在这种情况下， 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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