C++中标准输入流cin与Ctrl+Z使用时的问题

今天使用C++编写了一段小程序，练习使用标准库的算法，代码如下：

 1 #include 
 2 #include 
 3 #include 
 4 #include <string>
 5 
 6 using std::vector;
 7 using std::cin;
 8 using std::cout;
 9 using std::endl;
10 using std::string;
11 
12 int main() {
13     vector<string> vec;
14     string str;
15     cout << "Please enter some string..." << endl;
16     while (cin >> str) {
17         vec.push_back(str);
18     }
19     cout << "Please enter the key word: ";
20     cin >> str;
21     auto result = find(vec.cbegin(), vec.cend(), str);
22     if (result == vec.cend()) {
23         cout << "Failed to find the key word..." << endl;
24     } else {
25         cout << "Succeed to find the key word, it is the " << result - vec.cbegin() + 1 << "th word..." << endl;
26     }
27     system("pause");
28     return 0;
29 }

然而运行时却出现了问题，运行截图如下：

从运行结果来看，第20行的cin >> str;根本没有执行,于是输出cin的状态位看看出了什么问题:

1 cout << "cin.fail() = " << cin.fail() << endl;
2 cout << "cin.bad() = " << cin.bad() << endl;
3 cout << "cin.eof() = " << cin.eof() << endl;

可以看出，输入流cin的failbit以及eofbit已经被置位，但badbit没有置位，这说明cin流并没有崩溃，但是流已经到达了文件结束，IO操作失败，因此cin >> str;自然没有成功执行。

而问题出现的原因在于while(cin>>str)语句在结束输入时使用了Ctrl+Z，告诉cin用户已经结束了输入，所以eofbit与failbit被置位。

为了让程序正常运行，只需调用cin.clear()让cin的所有条件状态位复位，将状态设置为有效即可。

 1 #include 
 2 #include 
 3 #include 
 4 #include <string>
 5 
 6 using std::vector;
 7 using std::cin;
 8 using std::cout;
 9 using std::endl;
10 using std::string;
11 
12 int main() {
13     vector<string> vec;
14     string str;
15     cout << "Please enter some string..." << endl;
16     while (cin >> str) {
17         vec.push_back(str);
18         cout << "Push str = " << str << endl;
19     }
20     cout << "Please enter the key word: ";
21     cin.clear();
22     cin >> str;
23     cout << "str = " << str << endl;
24     cout << "cin.fail() = " << cin.fail() << endl;
25     cout << "cin.bad() = " << cin.bad() << endl;
26     cout << "cin.eof() = " << cin.eof() << endl;
27     auto result = find(vec.cbegin(), vec.cend(), str);
28     if (result == vec.cend()) {
29         cout << "Failed to find the key word..." << endl;
30     }
31     else {
32         cout << "Succeed to find the key word, it is the " << result - vec.cbegin() + 1 << "th word..." << endl;
33     }
34     system("pause");
35     return 0;
36 }

运行结果如下所示：

转载于:https://www.cnblogs.com/jzincnblogs/p/4994956.html