C ++输入验证 [英] C++ input validation

问题描述

我正在开始C ++编程，并且必须做很多输入验证.我发现此功能似乎普遍适用，但是在一个方面遇到了麻烦.如果我输入-90，则程序不会给出错误.我的问题是:1.如何添加输入不能小于等于0的情况?2.有没有更好的方法来限制用户的输入?也许是C ++中的库?

I am beginning C++ programming, and have to do a lot of input validation. I have found this function that seems universally applicable, but am having trouble with one aspect; If I were to type -90, the program doesn't give an error. my question(s) are: 1. How can I add the circumstance that input cannot be <= 0? 2. Is there a better way to limit users input? Maybe a library within C++?

感谢您的帮助或建议.

#include <ios>  // Provides ios_base::failure
#include <iostream>  // Provides cin

template <typename T>
T getValidatedInput()
{
    // Get input of type T
    T result;
    cin >> result;

    // Check if the failbit has been set, meaning the beginning of the input
    // was not type T. Also make sure the result is the only thing in the input
    // stream, otherwise things like 2b would be a valid int.
    if (cin.fail() || cin.get() != '\n')
    {
        // Set the error state flag back to goodbit. If you need to get the input
        // again (e.g. this is in a while loop), this is essential. Otherwise, the
        // failbit will stay set.
        cin.clear();

        // Clear the input stream using and empty while loop.
        while (cin.get() != '\n')
            ;

        // Throw an exception. Allows the caller to handle it any way you see fit
        // (exit, ask for input again, etc.)
        throw ios_base::failure("Invalid input.");
    }

    return result;
}

用法

inputtest.cpp

#include <cstdlib>  // Provides EXIT_SUCCESS
#include <iostream>  // Provides cout, cerr, endl

#include "input.h"  // Provides getValidatedInput<T>()

int main()
{
    using namespace std;

    int input;

    while (true)
    {
        cout << "Enter an integer: ";

        try
        {
            input = getValidatedInput<int>();
        }
        catch (exception e)
        {
            cerr << e.what() << endl;
            continue;
        }

        break;
    }

    cout << "You entered: " << input << endl;

    return EXIT_SUCCESS;
}

推荐答案

std :: istream :: operator>> 是根据 strtol ， strtoul 和表亲*，不幸的是，甚至对于无符号类型也总是接受减号.

std::istream::operator >> is defined in terms of strtol, strtoul, and cousins*, which unfortunately all invariably accept a minus sign even for unsigned types.

基本上，您所能做的就是接受带符号的int输入并将结果与​​零进行比较. std :: cin.setf(std :: ios :: failbit)人为地引发转换异常，因此您可以对转换函数在出现错误时应如何表现进行排序，但可能并非如此有很大帮助.

Essentially all you can do is accept signed int input and compare the result to zero. std::cin.setf( std::ios::failbit ) artificially raises a conversion exception, so you can sort-of emulate how the conversion function should behave on error, but that might not really be much help.

* operator>> 是根据 std :: num_get 定义的，而则是根据 scanf 定义的.根据 strto * 定义.每个人都刚刚通过，但是 strtoul 肯定是有缺陷的.

* operator >> is defined in terms of std::num_get, which is defined in terms of scanf, which is defined in terms of strto*. Everyone just passed the buck, but strtoul is pretty surely defective.

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