[英]overloaded assignment operator not working
我有一個 class員工。 (當我添加成員任務和任務列表時,我的一些評論沒有更新;對此我深表歉意。)
員工.h
#include <string>
#include <iostream>
using namespace std;
class Employee {
private:
string employee_name;
string employee_ssn;
string * taskList; //stores an array of tasks for the employee to do
int tasks; //stores the number of tasks an employee needs to do
public:
//constructors
Employee(); //default - nothing
Employee(string, string, string a[], int numOfTasks); //sets both ssn and name
~Employee(); //destructor
//copy constructor:
Employee(const Employee &emp);
Employee & operator =(const Employee& source);
void set_name(string); //sets name in program
void set_ssn(string); //sets ssn in program
string get_ssn(); //returns ssn as string
string get_name(); //returns emp name as string
void display(); //displays both on two separate lines
};
雇員.cpp
#include "Employee.h"
//constructors
//default constructor makes the object empty
Employee::Employee() {
taskList = nullptr;
return;
}
//constructor sets both name and ssn
Employee::Employee(string x, string y, string a[], int numOfTasks) {
employee_name = x;
employee_ssn = y;
tasks = numOfTasks;
taskList = a;
return;
}
//destructor
Employee::~Employee() {
delete [] taskList;
}
//copy constructor
Employee::Employee(const Employee & source) {
//copy simple member variables
employee_name = source.employee_name;
employee_ssn = source.employee_ssn;
tasks = source.tasks;
//allocate new dynamic array for taskList
taskList = new string[source.tasks];
//copy values from one taskList to another
for (int i = 0; i < tasks; i++)
taskList[i] = source.taskList[i];
return;
}
//assignment operator overloading
Employee & Employee::operator =(const Employee& source) {
cout << "Calling the assignment operator overloader.\n";
//check for self assignment
if (this == &source)
return *this; //avoid doing extra work
employee_name = source.employee_name;
employee_ssn = source.employee_ssn;
tasks = source.tasks;
cout << "Substituting 'task list'\n";
//delete former taskList
//if (taskList != nullptr)
delete[] taskList;
cout << "TaskList deleted.\n";
//allocate new one with same capacity
taskList = new string[source.tasks];
//copy values from one to the oher
for (int i = 0; i < tasks; i++)
taskList[i] = source.taskList[i];
cout << "Function complete.\n";
return *this;
}
//postcon: name is set to inputted string
void Employee::set_name(string s) {
employee_name = s;
return;
}
//postcon: ssn is set to inputted string
void Employee::set_ssn(string s) {
employee_ssn = s;
return;
}
//returns ssn as string
string Employee::get_ssn() {
return employee_ssn;
}
//returns employee name as string
string Employee::get_name() {
return employee_name;
}
//precon: name and ssn are both assigned
//postcon: name and ssn printed to the screen w/ labels on two lines
void Employee::display() {
cout << "Name: " << employee_name << endl;
cout << "SSN: " << employee_ssn << endl;
cout << "Tasks:\n";
for (int i = 0; i < tasks; i++)
cout << i + 1 << ". " << taskList[i] << endl;
return;
}
我們被指示實現復制構造函數和賦值重載,並且還特別指示我們在主程序中動態分配單個 Employee 對象。
我似乎遇到的問題是使用賦值重載進行交換。
員工驅動程序.cpp
#include "Employee.h"
#include <iostream>
int main() {
//tasks for each employee to do:
//Tasks to be assigned to Marcy:
string tasks[2] = {"Send emails", "Prepare meeting brief"};
//Taks to be assigned to Michael:
string tasks2[3] = {"Stock up on pens", "Send emails", "Organize union"};
Employee *emp1 = new Employee("Marcy", "678091234", tasks, 2);
Employee *emp2 = new Employee("Michael", "123994567", tasks2, 3);
//display data before swap
emp1->display();
cout << endl;
emp2->display();
cout << endl;
//swap employees
Employee temp(*emp1); //using copy constructor to copy first employee into temporary
*emp1 = *emp2;
*emp2 = temp; //uses overloaded assignment operator to copy values of temp into emp2; Marcy's data is now in Michael's pointer
//display after swap
cout << "\n\nAfter swap:\n\n";
emp1->display();
cout << endl;
emp2->display();
//free heap
delete emp1;
delete emp2;
//delete emp3;
return 0;
}
有問題的問題似乎發生在這里: *emp1 = *emp2;
(朝向主程序的底部),但我不知道為什么; 任何幫助,將不勝感激。 我可以繞過它,但我認為這不是練習的目的,我想知道為什么這個語句不能正常工作。
謝謝。
在構造函數內
Employee::Employee(string x, string y, string a[], int numOfTasks) {
employee_name = x;
employee_ssn = y;
tasks = numOfTasks;
taskList = a;
return;
}
您只需將傳遞的指針a
存儲在數據成員taskList
中,
主要是 arrays
string tasks[2] = {"Send emails", "Prepare meeting brief"};
//Taks to be assigned to Michael:
string tasks2[3] = {"Stock up on pens", "Send emails", "Organize union"};
不是動態分配的。 所以你可能不會在復制賦值運算符中調用運算符 delete [] 為這樣的 arrays
delete[] taskList;
您需要在構造函數中為數組動態分配一個指針,該指針作為參數傳遞給構造函數。
另請注意,在默認構造函數中,您需要將數據成員tasks
設置為 0。
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