将文件中的数据读入多个类对象C++

Question

如何使用默认类构造函数创建多个新类对象？

对于一个项目，我不得不编写一个将三个类对象写入文件的程序。我已经完成了......接下来的部分是能够使用readData函数将数据读回到三个单独的类对象中，然后显示数据。我完全失去了如何做到这一点，所以我没有readData函数中的任何代码。

下面是对象在写入文件时的样子。

employee name(21, "first last", "45 East State", "661-9000", 30, 12.00); 

这里是我的代码的大部分雇员类是相当基本的，但这里是默认的类构造函数。

employee::employee(); 
employee::employee(int locEmpNumber, string locName, string locaddress, string locphone, double locHrWorked, double locHrWage) 



#include "employee.h" 
#include <string> 
#include <iomanip> 
#include <iostream> 
#include <fstream> 
using namespace std; 

void writeData (const employee& e); 
void readData (const employee& e); 
void printCheck (const employee& e); 


int main() 
{ 
//Declarations 
const int ONE = 1; 
const int TWO = 2; 

int userInput; 

cout << "This program has two options:" << endl; 
cout << "1 - Create a data files called 'EmployeeInfo.txt', or" << endl; 
cout << "2 - Read data from a file and print paychecks." << endl; 
cout << "Please enter (1) to create a file or (2) to print checks: "; 

cin >> userInput; 

if (userInput == ONE) 
{ 
    //Create employee objects: 
    employee joe(37, "Joe Brown", "123 Main St.", "123-6788", 45, 10.00); 
    employee sam(21, "Sam Jones", "45 East State", "661-9000", 30, 12.00); 
    employee mary(15, "Mary Smith", "12 High Street", "401-8900", 40, 15.00); 

    ofstream empFile ("EmployeeInfo.txt"); 

    //Employee objects to write themselves out to the file. 
    writeData(joe); 
    writeData(sam); 
    writeData(mary); 

    //Close the file. 
    empFile.close(); 

    //Print an message that creation of the file is complete. 
    system("CLS"); 
    cout << "\nCreation of 'EmployeeInfo.txt' has completed.\n"; 
    cout << "\nYou can now run option 2.\n"; 

    //Exit. 
    system("PAUSE"); 
    return 0; 
} 
else if (userInput == TWO) 
{ 
    //Create three new Employee objects, using the default Employee constructor. 

    //Open the file that you just saved. 

    //Have each object read itself in from the file. 

    //Call the printCheck() function for each of the three new objects, just as you did in the previous project. 
} 
else 
{ 
    system("CLS");  
    cout << "Incorrect entry.... Please try again and follow directions closely! \n" << endl; 
    system("PAUSE"); 
    return 0; 
} 


} 

void writeData(const employee& e) 
{ 
fstream empFile; 
empFile.open ("EmployeeInfo.txt", ios::app); 

empFile << e.getEmpNumber() << "\n"; 
empFile << e.getName() << "\n"; 
empFile << e.getAddress() << "\n"; 
empFile << e.getPhone() << "\n"; 
empFile << e.getHrWorked() << "\n"; 
empFile << e.getHrWage() << "\n"; 
} 

void readData(const employee& e) 
{ 
fstream empFile;  
empFile.open ("EmployeeInfo.txt", ios::in); 

if(empFile.fail()) 
{ 
    cout << "File could not be open. Please try option 1 then option 2.\n" << endl; 
    return; 
} 

} 

Answer 1

很高兴看到您已经努力解决问题。但是，您在问题中提出的内容与代码中的某些注释之间存在不匹配。在我看来很清楚，你的简介的一个关键部分是员工对象本身必须能够自己写入文件并从文件中读回自己。

您已经编写了将对象内容写入文件的代码，而不是将对象写入文件。这看起来好像是我在分裂头发，但这是面向对象编程的本质。封装对象本身的功能是这里的真正目标。

我已经在下面包含一些代码来帮助你。希望这对你有好处。

class employee 
{ 
private: 
    int _locEmpNumber; 
    std::string _locName; 
    std::string _locAddress; 
    std::string _locPhone; 
    double _locHrWorked; 
    double _locHrWage; 

public: 
    employee(); 
    employee(int locEmpNumber, std::string locName, std::string locAddress, std::string locPhone, double locHrWorked, double locHrWage); 

    //object should be able to save itself as per your project brief. 
    void writeData(std::ofstream &empFile); 

    //object should be able to read itself from file as per your project brief 
    void readData(std::ifstream &empFile); 
}; 

employee::employee() 
{ 
    _locEmpNumber = 0; 
    _locHrWorked = _locHrWage = 0; 
} 


employee::employee(int locEmpNumber, std::string locName, std::string locAddress, std::string locPhone, double locHrWorked, double locHrWage) 
{ 
    _locEmpNumber = locEmpNumber; 
    _locName = locName; 
    _locAddress = locAddress; 
    _locPhone = locPhone; 
    _locHrWorked = locHrWorked; 
    _locHrWage = locHrWage; 
} 

// 
//From what I can glean from your brief ... 
//Employee objects to write themselves out to the file!!! 
void employee::writeData(std::ofstream &empFile) 
{ 
    empFile << _locEmpNumber << std::endl; 
    empFile << _locName << std::endl; 
    empFile << _locAddress<< std::endl; 
    empFile << _locPhone << std::endl; 
    empFile << _locHrWorked << std::endl; 
    empFile << _locHrWage << std::endl; 
} 

// 
//Again, from what I can glean from your brief ... 
//Have each object read itself in from the file!!! 
void employee::readData(std::ifstream &empFile) 
{ 
    //Normally you would have error handling in a method like this and 
    //would either return a response that indicates that the operation 
    //succeded or failed. You might alternatively use exception handling 
    //or indeed a combination of both. 
    // 
    //Normally you would reset all members to initial/empty values before 
    //reading values into them from your file. In this case we will omit that 
    //for the purposes of simplicity. The main reason you would reset members 
    //is to ensure that when reusing an object you don't end up with partial 
    //data from the current "read" operation mixed with partial data that 
    //was already in the object before you started reading. 
    std::string inputStr; 
    std::getline(empFile, inputStr); 
    _locEmpNumber = atoi(inputStr.c_str()); 
    std::getline(empFile, _locName); 
    std::getline(empFile, _locAddress); 
    std::getline(empFile, _locPhone); 
    std::getline(empFile, inputStr); 
    _locHrWorked = atof(inputStr.c_str()); 
    std::getline(empFile, inputStr); 
    _locHrWage = atof(inputStr.c_str()); 
} 


int main(int argc, char* argv[]) 
{ 
    //Declarations 
    const int ONE = 1; 
    const int TWO = 2; 

    int userInput; 

    std::cout << "This program has two options:" << std::endl; 
    std::cout << "1 - Create a data files called 'EmployeeInfo.txt', or" << std::endl; 
    std::cout << "2 - Read data from a file and print paychecks." << std::endl; 
    std::cout << "Please enter (1) to create a file or (2) to print checks: "; 

    std::cin >> userInput; 

    if (userInput == ONE) 
    { 
     //Create employee objects: 
     employee joe(37, "Joe Brown", "123 Main St.", "123-6788", 45, 10.00); 
     employee sam(21, "Sam Jones", "45 East State", "661-9000", 30, 12.00); 
     employee mary(15, "Mary Smith", "12 High Street", "401-8900", 40, 15.00); 

     std::ofstream empFile ("EmployeeInfo.txt"); 

     //Employee objects to write themselves out to the file. 
     joe.writeData(empFile); 
     sam.writeData(empFile); 
     mary.writeData(empFile); 
//  writeData(joe); 
//  writeData(sam); 
//  writeData(mary); 

     //Close the file. 
     empFile.close(); 

     //Print an message that creation of the file is complete. 
     system("CLS"); 
     std::cout << "\nCreation of 'EmployeeInfo.txt' has completed.\n"; 
     std::cout << "\nYou can now run option 2.\n"; 

     //Exit. 
     system("PAUSE"); 
     return 0; 
    } 
    else if (userInput == TWO) 
    { 
     //Create three new Employee objects, using the default Employee constructor. 
     employee joe; 
     employee sam; 
     employee mary; 

     //Open the file that you just saved. 
     std::ifstream empFile("EmployeeInfo.txt"); 

     //Have each object read itself in from the file. 
     joe.readData(empFile); 
     sam.readData(empFile); 
     mary.readData(empFile); 

     empFile.close(); 

     //Call the printCheck() function for each of the three new objects, just as you did in the previous project. 

     //I'll leave it to you to add this yourself. 
    } 
    else 
    { 
     system("CLS");  
     std::cout << "Incorrect entry.... Please try again and follow directions closely! \n" << std::endl; 
     system("PAUSE"); 
     return 0; 
    } 
    return 0; 
}