std::cin 不会在错误输入时引发异常 [英] std::cin doesn't throw an exception on bad input

问题描述

我只是想写一个简单的程序，从cin读取，然后验证输入是一个整数.如果是这样，我将跳出我的 while 循环.如果没有，我会再次要求用户输入.

I am just trying to write a simple program that reads from cin, then validates that the input is an integer. If it does, I will break out of my while loop. If not, I will ask the user for input again.

我的程序编译并运行得很好，这很棒.但是如果我输入一个非数值，它不会提示输入新的内容.什么给?

My program compiles and runs just fine, which is great. But it doesn't prompt for new input if I enter a non numeric value. What gives?

#include <iostream>
using namespace std;

int main() {
    bool flag = true;
    int input;
    while(flag){
        try{ 
            cout << "Please enter an integral value 
";
            cin >> input;
            if (!( input % 1 ) || input == 0){ break; }
        }
        catch (exception& e)
        { cout << "Please enter an integral value"; 
        flag = true;}
    }
    cout << input;
    return 0;
}

推荐答案

C++ iostreams 不使用异常，除非你告诉他们使用 cin.exceptions(/* 异常条件 */).

C++ iostreams don't use exceptions unless you tell them to, with cin.exceptions( /* conditions for exception */ ).

但是您的代码流更自然，无一例外.只需执行 if (!(cin >> input)) 等

But your code flow is more natural without the exception. Just do if (!(cin >> input)), etc.

还要记得在重试之前清除失败位.

Also remember to clear the failure bit before trying again.

整个事情可以是:

int main()
{
    int input;
    do {
       cout << "Please enter an integral value 
";
       cin.clear();
       cin.ignore(std::numeric_limits<std::streamsize>::max(), '
');
    } while(!(cin >> input));
    cout << input;
    return 0;
}

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