C++ 指定来自 istream 的输入并测试它

Question

我有一个 class 基本上表示一个元组（双 x，双 y），我重载了 << 运算符，所以我可以打印 class。现在我想对 >> 做同样的事情，所以它只支持以下格式： x, (x) 和 (x,y).

我有以下代码：

std::ostream & operator<< (std::ostream &output, tuple &c){
    output << "(" << c.x << "," << c.y << ")" << endl;
    return output;
}

std::istream & operator>> (std::istream & input, tuple &c){
    // Check for following patterns: x, (x) or (x,y)
}

我可以循环输入和正则表达式匹配吗？那怎么办呢？另外我怎么能测试它是否真的有效，就像这样 std::cin >> “(10.2,5.5)”
还是我需要读取文件进行测试？

编辑：给出的答案确实解决了这个问题，但我想添加一种方法来测试它，因为它可能会使用除我以外的其他人：

tuple x(6,2);
stringstream ss;
ss << x;
ASSERT_EQUALS(ss.str(), "(6,2)\n");

Answer 1

正则表达式对于像这样的简单输入任务来说是不必要的。这是我的做法，不检查是否有效输入，只是解析：

std::istream & operator>> (std::istream & input, tuple &c){
    // Check for following patterns: x, (x) or (x,y)
    char firstCharacter;
    input >> firstCharacter; // See what the first character is, since it varies

    if (firstCharacter == '(')
    {   // The simplest case, since the next few inputs are of the form n,n)
        char delimiters;
        input >> c.x >> delimiters >> c.y >> delimiters;
        //        N        ,           N        )
        // You also here have to check whether the above inputs are valid, 
        // such as if the user enters a string instead of a number
        // or if the delimeters are not commas or parentheses
    }
    else if (isdigit(firstCharacter) || firstCharacter == '-')
    {   //                               For negative numbers
        char delimiters;
        input.unget(); // Put the number back in the stream and read a number
        input >> c.x >> delimiters >> delimiters >> c.y >> delimiters;
        //        N           ,         (            N          )
        // You also here have to check whether the above inputs are valid, 
        // such as if the user enters a string instead of a number
        // or if the delimeters are not commas or parentheses
    }
    else
    { 
        // Handle some sort of a parsing error where the first character 
        // is neither a parenthesis or a number
    }

    return input;
}

Answer 2

聚会有点晚了，但这是正则表达式解决方案。虽然它不漂亮，但它允许输入负数和科学记数法。它还将容忍数字之间的空格：

#include <iostream>
#include <regex>
#include <tuple>

std::istream &operator>> (std::istream &input, std::tuple<double, double> &t)
{
    std::smatch m;
    std::string s;
    if (std::getline(input, s))
    {
        if (std::regex_match(s, m, std::regex(R"(\s*([-+]?\d*\.?\d+(?:[eE][-+]?\d+)?)\s*)"))) //x
            t = std::move(std::make_tuple(std::stod(m[1]), 0.0));
        else if (std::regex_match(s, m, std::regex(R"(\s*\(\s*([-+]?\d*\.?\d+(?:[eE][-+]?\d+)?)\s*\)\s*)"))) //(x)
            t = std::move(std::make_tuple(std::stod(m[1]), 0.0));
        else if (std::regex_match(s, m, std::regex(R"(\s*\(\s*([-+]?\d*\.?\d+(?:[eE][-+]?\d+)?)\s*,\s*([-+]?\d*\.?\d+(?:[eE][-+]?\d+)?)\s*\)\s*)"))) //(x,y)
            t = std::move(std::make_tuple(std::stod(m[1]), std::stod(m[2])));
    }
    return input;
}


int main() 
{
    std::tuple <double, double> t;
    std::cout << "Enter data in format num, (num) or (num1,num2): ";
    std::cin >> t;
    std::cout << "Tuple 0: " << std::get<0>(t) << std::endl;
    std::cout << "Tuple 1: " << std::get<1>(t) << std::endl;

    return 0;

}

C++ 指定来自 istream 的输入并测试它

C++ Specify input from istream and test it

c++

c++11

testing

istream