C++ Creating Array of Objects

Question

I'm having an issue with making one array with 3 objects. I'm trying to display the information of employees and my issue is that I don't know where I would assign the strings to the appropriate members and how to keep one variable for name. My code and an example are below:

class employee
{
private:                
    string name;
    string idNumber;

public:                 
    void setName(string);
    void setIDnumber(string);
    string getName();
    string getIDnumber();

};

const int numEmployees = 3;

int main()
{

    employee employeeInfo [numEmployees];
}

I want to create a constructor for 3 employees and input(name, idNumber). for example, in employeeInfo[0], the first employee, I want to input "Tom Jones", "123456" and in employee[1], the second employee, "James Blyth", "QE123"

Are you familiar with the notions of constructor and Implicitly-declared default constructor — Karen Baghdasaryan
– Karen Baghdasaryan, Commented Aug 19, 2021 at 22:09
@David___S__ How would you initialize a single employeeInfo, let alone an array of them? You've seemed to have skipped over the basic concept of constructors. — PaulMcKenzie
– PaulMcKenzie, Commented Aug 19, 2021 at 22:13
Are you familiar with arrays generally? employeeInfo[0] will be the first employee in the array, employeeInfo[1] will be the second, etc. There's not really anything special about it being an array of employee objects as opposed to an array of ints or floats or something. — Nathan Pierson
– Nathan Pierson, Commented Aug 19, 2021 at 22:14
So for example you could call employeeInfo[0].setName("Tom Jones"); to set the name of the first employee in the array to "Tom Jones" and employeeInfo[1].setIDnumber("QE123") — Nathan Pierson
– Nathan Pierson, Commented Aug 19, 2021 at 22:16

Remy Lebeau · Accepted Answer · 2021-08-19 22:26:09Z

You can simply call the setter methods on the individual employee objects, eg:

int main()
{
    employee employeeInfo [numEmployees];

    employeeInfo[0].setName("Tom Jones");
    employeeInfo[0].setIDNumber("123456");

    employeeInfo[1].setName("James Blyth");
    employeeInfo[1].setIDNumber("QE123");

    // and so on...

    ...
}

If you really want to add a constructor, then it would look like this:

class employee
{
private:                
    string name;
    string idNumber;

public:                 
    employee() = default;
    employee(string name, string idNumber);

    ...
};

employee::employee(string name, string idNumber) {
    setName(name);
    setIDnumber(idNumber);
};

...

int main()
{
    employee employeeInfo [numEmployees];

    employeeInfo[0] = employee("Tom Jones", "123456");
    employeeInfo[1] = employee("James Blyth", "QE123");
    // and so on...
}

Just note that this will default-construct the array elements first, and then construct temporary objects to overwrite the array elements.

If you want to avoid the temporaries, but still want a fixed array of objects stored consecutively, you can use placement-new to construct the array members directly using your non-default constructor, eg:

#include <type_traits>

int main()
{
    std::aligned_storage_t<sizeof(employee), alignas(employee)> buffer[numEmployees];
    employee* employeeInfo = reinterpret_cast<employee*>(buffer);

    new(&employeeInfo[0]) employee("Tom Jones", "123456");
    new(&employeeInfo[1]) employee("James Blyth", "QE123");
    // and so on...

    ...

    for(int i = 0; i < numEmployees; ++i) {
        employeeInfo[i].~employee();
    }
}

Or, you can use a std::vector (if you don't mind the array being allocated in dynamic memory), eg:

#include <vector>

int main()
{
    std::vector<employee> employeeInfo;
    employeeInfo.reserve(numEmployees);

    employeeInfo.emplace("Tom Jones", "123456");
    employeeInfo.emplace("James Blyth", "QE123");
    // and so on...

    ...
}

Otherwise, create an array of pointers to objects instead, and then you can create the individual objects dynamically using new with your non-default constructor. The objects just won't be stored consecutively in memory, eg:

int main()
{
    employee* employeeInfo[numEmployees];

    employeeInfo[0] = new employee("Tom Jones", "123456");
    employeeInfo[1] = new employee("James Blyth", "QE123");
    // and so on...

    ...

    for(int i = 0; i < numEmployees; ++i) {
        delete employeeInfo[i];
    }
}

Which would be safer handled with std::unique_ptr, eg:

#include <memory>

int main()
{
    std::unique_ptr<employee> employeeInfo[numEmployees];

    employeeInfo[0] = std::make_unique<employee>("Tom Jones", "123456");
    employeeInfo[1] = std::make_unique<employee>("James Blyth", "QE123");
    // and so on...

    ...
}

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