问题描述

我正在尝试使用 istringstream 将一个简单的字符串拆分为一系列整数:

I'm trying to use istringstream to split a simple string into a series of integers:

#include <string>
#include <iostream>
#include <sstream>
#include <vector>

using namespace std;

int main(){

    string s = "1 2 3"; 
    istringstream iss(s);   

    while (iss)
    {
        int n;
        iss >> n;
        cout << "* " << n << endl;
    } 
}

我得到:

* 1
* 2
* 3
* 3

为什么最后一个元素总是出现两次?如何解决?

Why is the last element always coming out twice? How to fix it?

推荐答案

它出现了两次，因为你的循环是错误的，正如在 http://www.parashift.com/c++-faq-lite/input-output.html#faq-15.5 (在这种情况下，while (iss) 与 while (iss.eof()) 没有什么不同.

It's coming out twice because your looping is wrong, as explained (indirectly) at http://www.parashift.com/c++-faq-lite/input-output.html#faq-15.5 (while (iss) is not dissimilar from while (iss.eof()) in this scenario).

具体来说，在第三次循环迭代中，iss >>n 成功并获取您的 3，并使流保持良好状态.由于这种良好的状态，循环然后第四次运行，直到下一次(第四次)iss>>n 随后失败，循环条件被破坏.但是在第四次迭代结束之前，您仍然输出 n... 第四次.

Specifically, on the third loop iteration, iss >> n succeeds and gets your 3, and leaves the stream in a good state. The loop then runs a fourth time due to this good state, and it's not until the next (fourth) iss >> n subsequently fails that the loop condition is broken. But before that fourth iteration ends, you still output n... a fourth time.

试试:

#include <string>
#include <iostream>
#include <sstream>
#include <vector>

using namespace std;

int main()
{
    string s = "1 2 3"; 
    istringstream iss(s);   
    int n;

    while (iss >> n) {
        cout << "* " << n << endl;
    } 
}

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