为什么循环 for stringstream 两次给我最后一个词

Question

我试图在 stringstream 的帮助下逐字循环字符串，这是我的代码：

string str = "hello world";
stringstream ss(str);
string word;
while (ss)
{
    ss >> word;
    cout << word << endl;
}

然而，我得到的结果如下：

hello
world
world

为什么我得到了两次world？

Answer 1

while (ss) 看到 ss 还没有遇到问题，所以它运行循环体。（这就是当您将 ss 用作布尔值时发生的情况）
ss >> word; 读取 "hello"
cout << word << endl; 打印 "hello"
while (ss)看到ss还没有遇到问题，所以再次运行循环体。
ss >> word; 读取 "world"
cout << word << endl; 打印 "world"
while (ss)看到ss还没有遇到问题，所以再次运行循环体。
ss >> word;看到没有更多的数据，所以失败。 word不变，仍然包含"world"
cout << word << endl; 打印 "world"
while (ss) 发现 ss 遇到问题并停止循环。

您需要检查在读完这个词后是否停止循环。例如，使用：

while (true)
{
    ss >> word;
    if (!ss)
        break;
    cout << word << endl;
}

或简称：

while (ss >> word)
{
    cout << word << endl;
}

Answer 2

使用此代码片段：

while (ss) { ... }

您正在检查 string stream 的状态。如果它包含有效数据，循环将继续。这就是为什么您两次看到最后一个词的原因...

1^st iteration of loop:

while ( ss ) {             // checks if there is valid data in ss and for errors (true)
    ss >> word;            // ss inserts "hello" into word.
    cout << word << endl;  // cout prints "hello" to the console.
}

2^nd iteration of loop:

while ( ss ) {             // checks again if there is valid data (true)
    ss >> word;            // ss inserts "world" into word.
    cout << word << endl;  // cout prints "world" to the console.
}

3^rd iteration of loop:

while ( ss ) {             // checks again if there is valid data (true)
    ss >> word;            // ss already contains "world", may optimize or copy over...
    cout << word << endl;  // cout prints "world" to the console.
}

4^th iteration of loop:

while ( ss ) {             // ss encountered end of stream (false) exits loop.
    ss >> word;            // nothing inserted as loop has exited.
    cout << word << endl;  // nothing printed as loop has exited.
}

与其尝试将 stringstream 用作循环条件，不如尝试使用从 stringstream 中提取数据并将其转化为条件变量的过程。

while( ss >> word ) {
    cout << word << endl;
}

1^st iteration of loop:

while ( ss >> word ) {       // checks if ss inserted data into word
                             // ss inserts "hello" (true)
    cout << word << endl;    // cout prints "hello" to the console.
}

2^nd iteration of loop:

while ( ss >> word ) {      // checks again if ss inserted data into word
                            // ss inserts "world" into word (true)
    cout << word << endl;   // cout prints "world" to the console.
}

3^rd iteration of loop:

while ( ss >> word ) {      // checks again if ss inserted data into word
                            // ss fails to insert data (false) loop exits here
    cout << word << endl;   // nothing printed as loop exited
}

为什么循环 for stringstream 两次给我最后一个词

Why does loop for stringstream give me the last word twice

c++

string

stringstream