Classes

[Rascal]

Hi,

I am working on the question below.

Consider the following class declaration:

class Employee
{
public:
Employee ();
string getName();
private:
bool citizen();
string lastName;
string firstName;
string employeeNumber;
};

Explain what is wrong with the following code fragment:

int main()
{
Employee e;
……
string eNumber = e.employeeNumber;
return 0;
}

I have attempted to merge the 2 pieces of code with omitting the ......, but this errored out as there was no:
#include <iostream>
#include <string>
using namespace std;

so i have added these in to have the code below.

#include <iostream>
#include <string>

using namespace std;

class Employee
{
public:
Employee ();
string getName();
private:
bool citizen();
string lastName;
string firstName;
string employeeNumber;
};

int main()
{
Employee e;
string eNumber = e.employeeNumber;
return 0;
}

which at line 15 I receive:
error: 'std::string Employee::employeeNumber' is private'
and at line 21:
error: within this context

Could anyone help with the detail that the instructor would be looking for to answer this question as I don't think that the extracts from the line errors above is what is expected.

Thanks again.

[zb0S216C]

"Employee::employeeNumber" is private. In general, private data-members cannot be read from or written to by a function or class that's neither a friend class, friend function or member-function.

You have a few choices to overcome this problem:

1) Friends. A friend of a class is either a function or another class that's allowed to read or write to private data-members directly. Here's an example:

class Something
{
  int X;

  public:
    friend int ReadXFromSomething( Something &Object );
};

int ReadXFromSomething( Something &Object )
{
  return( Object.X );
}

Here, "ReadXFromSomething( )" is a friend of "Something" and is allowed direct access to the data-members of another "Something" object.

2) Getters. Getters are the counterpart of setters. Getters obtain the value of a data-member. It's common practice (and preferred) for getters member-functions to return either a non-constant copy or a constant reference to some data-member.

class Something
{
  private:
    int X;

  public:
    int GetXCopy( ) const
    {
      return( X );
    }
};

Here, "Something::GetXCopy( )" is a getter. Note the "const" qualifier; it's used to tell the compiler that the data-members will not be modified during the call to "Something::GetXCopy( )". It's common for getters to be declared this way.

Both of the above solutions respect the encapsulation concept when applied correctly. Please, in the future, avoid setters at all costs.

_Wazzak