c++ - while (_index != string::npos) 似乎并没有停止循环

Question

我的代码计算字符串 temp 中的空格，效果很好。在代码的后面，我有一个类似的循环，但没有按预期结束。

根据我的调试和一些研究，我确定 while 循环没有在应该停止的时候停止第二次，因此抛出异常(std::out_of_range )… 为什么？两个 while 循环的条件相同，所以它们的行为应该相同，对吧？也就是说，当 find() 没有找到空格时，它们都应该停止循环……

第一部分代码:

// Just find out how many spaces are in the temp string for now
// Find index (position in the string) of the first space in temp string
_index = temp.find( " " );

// Loop as long as there are still spaces in temp string
while (_index != string::npos) {
    // Find the index of the next space
    _index = temp.find(" ", _index + 1);

    // Keep track of how many spaces are in temp string
    count++;
}

稍后(不要介意我的调试代码穿插其中):

// If the amount of spaces is just right, i.e. there are exactly SIZE - 1 spaces
if (count == SIZE - 1) {
    cout << "\n\n  - Inside the if (count == SIZE - 1) block\n"
         << "  - temp = \"" << temp << "\", temp's size = " << temp.length()
         << "\n\n";

    // This time, we're removing the spaces from the temp string in order to
    // be able to search it for any non-number characters
    // Find index of the first space in the temp string
    _index = temp.find(" ");

    cout << "  - The first temp.find(\" \") yields: " << _index << "\n\n";

    // Loop as long as there are still spaces in temp string
    while (_index != string::npos) {
        cout << "  - Right before temp.replace() in the loop\n"
             << "  - _index = " << _index << "\n\n";

        // Remove the space in temp string
        temp.replace(_index, 1, "");

        // find the index of the next space
        _index = input.find(" ", _index + 1);
    }
    // …
}

Answer 1

在第二个循环中，您引用了一个变量 input 而不是 temp。

_index = input.find( " ", _index + 1 );`

因此循环永远不会终止。您不会在第一个 while 循环中执行此操作。