cin.clear()和cin.ignore()不能工作

Question

我对这个问题做了大量的研究，找到了一些答案并修正了我的代码，但我仍然无法让cin.clear()和cin.ignore()工作。这是我所指的代码的一部分：

if(cityname1 == "Error" || cityname2 == "Error")
{
    cout << "**********ERROR! PLEASE ENTER 0-5 FOR YOU LOCATIONS**********" << endl << endl;
    cin.clear();
    cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    detailLoop();
}
else
{
    cout << "The distance from " << cityname1 << " to " << cityname2;
    cout << " is approximately " << cityarray[start][finish] << " miles." << endl << endl;
}

如果用户输入一个0-5以外的数字，就会输出错误消息，但是如果他们输入了一个字符，代码就会进入无限循环。在做完这项研究之后，我觉得这段代码应该可以工作，但不幸的是，我无法理解它。此外，我是一个初学者，所以如果有人对这是写的方式有意见，请批评！这是整个函数，如果这有帮助的话。我做了#include<limits>。

void detailLoop()
{
//initializes array(letters in comments stand for city;
//array values are the distances)
int cityarray[6][6] = {
    //DB-DB,DB-G,DB-J,DB-M,DB-Tall,DB-Tampa
    0,97,90,268,262,130,

    //G-DB,G-G,G-J,G-M,G-Tall,G-Tampa
    97,0,74,337,144,128,

    //J-DB,J-G,J-J,J-M,J-Tall,J-Tampa
    90,74,0,354,174,201,

    //M-DB,M-G,M-J,M-M,M-Tall,M-Tampa
    268,337,354,0,475,269,

    //Tall-DB,Tall-G,Tall-J,Tall-M,Tall-Tall,Tall-Tampa
    262,144,174,475,0,238,

    //Tampa-DB,Tampa-G,Tampa-J,Tampa-M,Tampa-Tall,Tampa-Tampa
    130,128,201,269,238,0
    };

//starting location
int start = 0;
//destination
int finish = 0;
//strings used to print city names
string cityname1;
string cityname2;
//menu block
cout << "Choose locations from the menu below:" << endl;
cout << "0 - Daytona Beach" << endl;
cout << "1 - Gainesville" << endl;
cout << "2 - Jacksonville" << endl;
cout << "3 - Miami" << endl;
cout << "4 - Tallahassee" << endl;
cout << "5 - Tampa" << endl << endl;

//user input for starting city
cout << "Enter your starting location: > "; cin >> start;

//user input for ending city
cout << "Enter your destination: > "; cin >> finish; cout << endl;

//assigns names to cityname1 so it can be printed
switch(start)
{
case 0:
    cityname1 = "Daytona Beach";
    break;
case 1:
    cityname1 = "Gainesville";
    break;
case 2:
    cityname1 = "Jacksonville";
    break;
case 3:
    cityname1 = "Miami";
    break;
case 4:
    cityname1 = "Tallahassee";
    break;
case 5:
    cityname1 = "Tampa";
    break;
default:
    cityname1 = "Error";
    break;
}

//assigns names to cityname2 so it can be printed
switch(finish)
{
case 0:
    cityname2 = "Daytona Beach";
    break;
case 1:
    cityname2 = "Gainesville";
    break;
case 2:
    cityname2 = "Jacksonville";
    break;
case 3:
    cityname2 = "Miami";
    break;
case 4:
    cityname2 = "Tallahassee";
    break;
case 5:
    cityname2 = "Tampa";
    break;
default:
    cityname2 = "Error";
    break;
}

if(cityname1 == "Error" || cityname2 == "Error")
{
    cout << "**********ERROR! PLEASE ENTER 0-5 FOR YOU LOCATIONS**********" << endl << endl;
    cin.clear();
    cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    detailLoop();
}
else
{
    cout << "The distance from " << cityname1 << " to " << cityname2;
    cout << " is approximately " << cityarray[start][finish] << " miles." << endl << endl;
}
}

Answer 1

您应该使用cin.fail()以及您的条件

if(cin.fail()||cityname1 == "Error" || cityname2 == "Error")
{
cout << "**********ERROR! PLEASE ENTER 0-5 FOR YOU LOCATIONS**********" << endl << endl;
cin.clear();
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
detailLoop();
}

Answer 2

最后，我发现所有这些打字的读者都是无用和疯狂的，他们试图为阅读交互式的输入而工作。你基本上结束了与终端和输入缓冲区的战斗。

在处理交互式会话的标准输入和解析-重新提示时，cin.clear()没有做任何合理的事情。你不应该这么叫。

用cin.getline()重写所有内容并解析产生的字符串，您将能够理解并修复这些失败模式。

Answer 3

如果您的代码工作很好，如果您的main()如下所示：

int main() { detailLoop(); }

我怀疑您是从循环中调用detailLoop，这将导致无限循环。