c++ - 超过 8 个字符的字符串会导致无限循环 C++

Question

我的 C++ 代码有问题，而且我还没有真正在网上找到任何描述为什么我有这个问题的信息。这是我的代码:

/*
Write a program using vectors and iterators that allows a user to main-
tain a list of his or her favorite games. The program should allow the
user to list all game titles, add a game title, and remove a game title.
*/

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
    vector<string> gamesList;
    gamesList.reserve(10);
    vector<string>::const_iterator iter;
    string menu = "1. List all games\n";
    menu += "2. Add a game title\n";
    menu += "3. Remove a game title\n";
    menu += "4. Quit\n";
    string newTitle = "", removeTitle = "";
    int choice = 0;

    while (choice != 4)
    {
        cout << menu;
        cout << "\nYour choice: ";
        cin >> choice;
        switch (choice)
        {
            case 1:
                for (iter = gamesList.begin(); iter != gamesList.end(); ++iter)
                {
                    cout << *iter << endl;
                }
                cout << "\nList capacity is " << gamesList.capacity() << endl;
                break;
            case 2:
                cout << "Please enter a game title :";
                cin >> newTitle;
                gamesList.push_back(newTitle);
                break;
            case 3:
                cout << "Which game title do you want to remove?\n";
                cin >> removeTitle;
                for (int i = 0; i < gamesList.size(); ++i)
                {
                    if (gamesList[i] == removeTitle)
                    {
                        gamesList.erase(gamesList.begin() + i);
                    }
                }
                break;
            case 4:
                cout << "Good bye!";
                break;
        }
    }
    return 0;
}

如果我运行该程序并在列表中输入 Pong、Breakout 和 Tetris，它运行良好。如果我运行该程序并输入 Half Life 或任何长度超过 8 个字符的标题，该程序将进入无限循环。任何帮助将不胜感激。

Answer 1

问题不在于长度，而是您尝试输入的名称中包含 空格。输入运算符 >>> 在空格上分隔。因此，如果您输入 Half Life 作为名称，输入运算符将只会读取 Half。

你可能应该使用 std::getline相反，阅读名称。

至于无限循环，这是因为由于部分名称仍在输入缓冲区中(带有前导空格)，因此当您尝试读取菜单项的数字时，输入将失败，将输入保留在缓冲区，你不会检测到它并进入一个无限循环，你想在其中读取一个整数，失败并不断...

使用 std::getline 将解决这两个问题。但是如果你想确保这种情况不会再次发生，你必须在读取菜单选项的整数时添加一些错误检查。这可以简单地类似于

while (!(cin >> choice))
{
    // Input of menu alternative failed, ignore input until the end of the line
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}

An std::istream::ignore reference .