c++ - 为什么我的对象 vector 中的元素在调用对象成员函数之一时没有更新？

Question

很长一段时间以来，我一直在尝试使用 visual studio 调试器对此进行调试，但我无法弄清楚为什么我的函数 emp.setHoursWorked(hWorked);在 recordHoursWorkedForEmployee似乎只是更新 numOfHoursWorked而在 recordHoursWorkedForEmployee , 一旦程序退出函数 numOfHoursWorked vector 中的所有员工返回 0。下面是有问题的代码。任何帮助将不胜感激。

#ifndef PAYROLLSYSTEM   
#define PAYROLLSYSTEM
#include "Employee.h"
#include "Paycheck.h"
#include <string>
#include <vector>

using namespace std;

class PayRollSystem
{
public:

    //custom constructor gets company name
    PayRollSystem(string);
    void createEmployee(string, string,string, double);
    void removeEmployee(string);
    void recordHoursWorkedForEmployee(string);
    void issuePaychecks();


private:
    string companyName;
    vector<Employee> companyEmployees;
};
#endif



void PayRollSystem::createEmployee(string empId, string fName, string lName, double hWage)
{
    Employee temEmp = Employee(empId, fName, lName, hWage);
    companyEmployees.push_back(temEmp);

}


void PayRollSystem::recordHoursWorkedForEmployee(string empId)
{

    for (Employee emp : companyEmployees)
    {

        if (emp.getEmployeeId() == empId)
        {
            int hWorked = 0;
            cout << "What are the hours the worked for " + emp.getEmployeeId() + " during current pay period?" << endl;
            cin >> hWorked;

            //TODO: For some reason this line is not updating the hours worked. Must fix!
            emp.setHoursWorked(hWorked);
            cout << "Hours for " + emp.getEmployeeId() + " have been changed to " << emp.getHoursWorked() << endl;
        }
    }

}

我在这里排除头文件是为了不粘贴太多与我面临的问题无关的东西，只提供与所提供问题相关的成员函数的实现

//Overloaded constructor to be used with PayRollSystem
Employee::Employee(string empId, string fName, string lName, double hWage)
{
    employeeId = empId;
    firstName = fName;
    lastName = lName;
    hourlyWage = hWage;
    numOfHoursWorked = 0;

}

void Employee::setHoursWorked(int hWorked)
{
    if (hWorked >= 0)
        numOfHoursWorked = hWorked;
    else
    {
        cout << "Invalid number of hours worked." << endl;
        exit(EXIT_FAILURE);
    }
}

string Employee::getEmployeeId() const
{
    return employeeId;
}

Answer 1

此行复制每个员工:

for (Employee emp : companyEmployees)

变量emp 是容器中对象的拷贝。因此，如果您更新它，您只是在更新拷贝。每次迭代您都会将一个新值复制到 emp 中，但任何更改都不会反射(reflect)在原始对象中。

你的意思可能是:

for (Employee& emp : companyEmployees)
            ^^^

这里的 emp 是对 vector 内部对象的引用。如果你修改它，你就是在修改 vector 中的原始值。