使用 cin 的良好输入验证循环 - C++
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Good input validation loop using cin - C++
提问by Alex
I'm in my second OOP class, and my first class was taught in C#, so I'm new to C++ and currently I am practicing input validation using cin. So here's my question:
我在上我的第二堂 OOP 课，我的第一堂课是用 C# 教授的，所以我是 C++ 的新手，目前我正在使用 cin 练习输入验证。所以这是我的问题：
Is this loop I constructed a pretty good way of validating input? Or is there a more common/accepted way of doing it?
我构建的这个循环是一种很好的验证输入的方法吗？或者有更常见/接受的方式吗？
Thanks!
谢谢！
Code:
代码：
int taxableIncome;
int error;
// input validation loop
do
{
error = 0;
cout << "Please enter in your taxable income: ";
cin >> taxableIncome;
if (cin.fail())
{
cout << "Please enter a valid integer" << endl;
error = 1;
cin.clear();
cin.ignore(80, '\n');
}
}while(error == 1);
回答by P-Nuts
I'm not a huge fan of turning on exceptions for iostreams. I/O errors aren't exceptional enough, in that errors are often very likely. I prefer only to use exceptions for less frequent error conditions.
我不太喜欢为 iostreams 打开异常。I/O 错误还不够特殊，因为错误通常很可能发生。我更喜欢只在不太频繁的错误情况下使用异常。
The code isn't bad, but skipping 80 characters is a bit arbitrary, and the error variable isn't necessary if you fiddle with the loop (and should be boolif you keep it). You can put the read from cindirectly into an if, which is perhaps more of a Perl idiom.
代码还不错，但是跳过 80 个字符有点随意，如果您摆弄循环，则不需要错误变量（bool如果您保留它应该是）。您可以将 read fromcin直接放入 an 中if，这可能更像是 Perl 习语。
Here's my take:
这是我的看法：
int taxableIncome;
for (;;) {
cout << "Please enter in your taxable income: ";
if (cin >> taxableIncome) {
break;
} else {
cout << "Please enter a valid integer" << endl;
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
}
}
Apart from only skipping 80 characters, these are only minor quibbles, and are more a matter of preferred style.
除了只跳过 80 个字符外，这些只是小问题，更多的是首选风格。
回答by ari-free
int taxableIncome;
string strInput = "";
cout << "Please enter in your taxable income:\n";
while (true)
{
getline(cin, strInput);
// This code converts from string to number safely.
stringstream myStream(strInput);
if ( (myStream >> taxableIncome) )
break;
cout << "Invalid input, please try again" << endl;
}
So you see I use string for input and then convert that to an integer. This way, someone could type enter, 'mickey mouse' or whatever and it will still respond.
Also #include <string>and <sstream>
所以你看到我使用字符串作为输入，然后将其转换为整数。这样，有人可以输入回车、“米老鼠”或其他任何东西，它仍然会响应。
还有#include<string>和<sstream>
回答by Mawg says reinstate Monica
Might you not consider try/catch, just to get you used to the concept of exception handling?
你可能不考虑 try/catch，只是为了让你习惯异常处理的概念？
If not, why not use a boolean, instead of 0 and 1? Get into the habit of using variables of the correct type (and of creating types where needed)
如果不是，为什么不使用布尔值，而不是 0 和 1？养成使用正确类型变量的习惯（并在需要时创建类型）
Cin.fail() is also discussed at http://www.cplusplus.com/forum/beginner/2957/
http://www.cplusplus.com/forum/beginner/2957/也讨论了 Cin.fail()
In fact, in many places ...
其实很多地方...
you might study some of those and try to follow the explanations of why things should be done a certain way.
您可能会研究其中的一些，并尝试遵循有关为什么应该以某种方式完成工作的解释。
But, sooner or later, you ought to understand exceptions...
但是，迟早你应该了解异常...
回答by R Samuel Klatchko
One minor quibble is that the error helper variable is completely redundant and is not needed:
一个小问题是错误辅助变量是完全多余的，不需要：
do
{
cin.clear();
cout << "Please enter in your taxable income: ";
cin >> taxableIncome;
if (cin.fail())
{
cout << "Please enter a valid integer" << endl;
cin.ignore(80, '\n');
}
}while(cin.fail());
