如何在 C++ 中实现 istream 和重载？

Question

我无法获取此代码来输出文件信息。我将如何使用 ostream 重载来输出这个？还是我必须以其他方式做到这一点？我想不通。

哪种 C++ 排序算法最适合用于对信息升序排序？

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <stdlib.h> // needed to use atoi function to convert strings to integer

using namespace std;

struct Employees
{
   string employeeName;
   string employeeID;
   int rate;
   int hours;
};

istream& operator >> (istream& is, Employees& payroll)
{
    char payrollStuff[256];
    int pay = atoi(payrollStuff); // use atoi function to convert string to int

    is.getline(payrollStuff, sizeof(payrollStuff));
    payroll.employeeName = payrollStuff;

    is.getline(payrollStuff, sizeof(payrollStuff));
    payroll.employeeID = payrollStuff;

    is.getline(payrollStuff, sizeof(payrollStuff));
    payroll.rate = atoi(payrollStuff);

    is.getline(payrollStuff, sizeof(payrollStuff));
    payroll.hours = atoi(payrollStuff);

    return is;

};

int main()
{
    const int SIZE = 5; // declare a constant
    Employees payroll_size[5];

    ifstream myFile;
    myFile.open("Project3.dat");
    if(myFile.fail())            //is it ok?
   {
       cerr << "Input file did not open please check it" << endl;
   }
   else
   for (int i=0; i< 5; i++)
   {
       myFile >> payroll_size[i];
   }


   myFile.close();

   return 0;
}

Answer 1

只需像 >> 那样重载运算符即可。例如：

ostream& operator<<(ostream& os, Employees& payroll)
{
    os << payroll.employeeName << " " << payroll.employeeID << " " << payroll.rate << " " << payroll.hours << "\n";
    return os;
}

然后，在一个循环中，您可以遍历数组并使用<< 打印出每个Employees。

附带说明，如果您正在检查文件是否打开，最好使用专用函数std::ifstream::is_open。

对于您的条目进行排序，最好使用std::sort，并为您想要排序的任何标准使用自定义谓词。例如，如果您想根据 Employee 的姓名按字母顺序进行排序，您可以使用以下命令：

sort(payroll_size, payroll_size + 5, [](const Employee& a, const Employee& b) { return a.employeeName < b. employeeName; });