Creating multiple objects in a class

Question

I'm confused on how to put numerous objects into a class. So we are required to read in a file that contains a timestamp, employee ID, location number, event code. An example of the input is:

10039865 WHITE99 1 OP
10039876 WHITE99 1 EN
10047500 PINK01 1 EN
10047624 SMITH01 3 EX
10047701 TAN07 2 EN
10048567 DIITZ01 2 OP
10048577 DIITZ01 2 OP
10048587 DIITZ01 2 OP

how do I set those information into objects in a class? here is what I got so far, and stuck from here. We are required to write a program using an array of pointers to objects.

class Employee {

    long timestamp;
    string staffID;
    int locNum;
    string eventCode;

public:
    void setValues (long, string, int, string);

};

void Employee::setValues(long timestamp, string staffID, int locNum, string eventCode) {
    this->timestamp = timestamp;
    this->staffID = staffID;
    this->locNum = locNum;
    this->eventCode = eventCode;
}

Create an object, and call the setValues member with the correct values from one line? — Some programmer dude
– Some programmer dude, Commented Aug 22, 2017 at 3:50
Off topic: "We are required to write a program using an array of pointers to objects" Complete the assignment as required, but know this: You will almost never want to do this in real programming. Also explains why this poor sucker looks like they are trying to code their way into a deep hole. — user4581301
– user4581301, Commented Aug 22, 2017 at 3:56
On topic: Zip on down to the section on Bitshift Operators (used for Stream I/O) and give it a read. Build into the >> operator Option 2 from this answer and you should be on your way with code that looks something like while(file >> emplyeelist[count]) count++; — user4581301
– user4581301, Commented Aug 22, 2017 at 4:01
"We are required to write a program using an array of pointers to objects." Well then, create an array of pointers to Employee objects, read from the file line-by-line to create and fill an Employee object and then insert its address into the array created earlier. — CinCout
– CinCout, Commented Aug 22, 2017 at 4:17
Can you show me how to do that? I'm still new at coding, so I'm not really sure how to implement this. — futilecheese28
– futilecheese28, Commented Aug 22, 2017 at 6:59

NonCreature0714 · Accepted Answer · 2017-08-22 07:21:50Z

0

I'm going to leave out a few things, since this looks like homework, but this will get you far.

A couple of things to watch out for:

You aren't using a constructor. Sure a default constructor is nice, but it can help to make your own, especially when starting out.
You should probably use vector instead of an array.

For example:

// Note that I'm making the members public - this is only for demonstration so I don't have to write getters and setters.
class Employee {
    public:
    Employee(long, std::string, int, std::string);
    long timestamp;
    std::string staffID;
    int locNum;
    std::string eventCode;
};

// Here is the constructor.
Employee::Employee(long l, std::string s, int n, std::string s2): timestamp(l), staffID(s), locNum(n),  eventCode(s2){}

As for an array - it may be wiser to stick to using a vector of Employee pointers. Such as:

typedef Employee * EmployeePointer;    
EmployeePointer employeePtr;
std::vector<EmployeePointer> employeeVec;

Then .push_back() new Employees using your fancy new constructor with a pointer.

employeePtr = new Employee(181213, "Bob", 22, "OP");
employeeVec.push_back(employeePtr);

And simply re-use the employeePtr for new employees.

employeePtr = new Employee(666732, "Sue", 21, "MA");
employeeVec.push_back(employeePtr);

And you will see that a vector (which most other languages refer to as an Array anyway) of pointers to employee objects is created:

for(auto it = employeeVec.begin(); it != employeeVec.end(); it++){
    std::cout << (*it)->timestamp << " " << (*it)->staffID << " " << (*it)->locNum << " " << (*it)->eventCode << std::endl;
}

Which displays:

181213 Bob 22 OP
666732 Sue 21 MA

If you can't use vector for whatever reason then implementing this with an array isn't that different, except.

EmployeePointer empPtrArr;

// You'll need to know the size of your array of pointers or else dynamically allocate it, which I don't think you want to do.
empPtrArr = * new EmployeePointer[2];

And You'll have to use a basic for-loop, and not that fancy for(auto ... ) one I used.

Final comments:

For every 'new' there is a 'delete', or you'll have a memory leak
There is at least one #include I left out for you to figure out, which shouldn't be difficult to find

edited Aug 22, 2017 at 7:21

answered Aug 22, 2017 at 7:02

NonCreature0714

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4 Comments

NonCreature0714 Over a year ago

@Macmade agreed! Though OP needs a collection of pointers to objects, and I don't know OP's experience or restrictions - so thought it was a simple way to appease a starting level should vectors be ruled out. What is your alternative?

futilecheese28 Over a year ago

Thank you! This helped me a lot. Our professor is limiting us in using arrays since we have not discussed vectors or maps in class yet. I have a question about the pointers to employee objects. Since I am using an array, how would I do it?

NonCreature0714 Over a year ago

@futilecheese28 stackoverflow.com/questions/620843/… I believe the second answer will get you were you want. You'll notice this question is similar to your own ;)

NonCreature0714 Over a year ago

@Macmade that does make things more simple - I'll update it soon

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