Polymorphism

[Pieter]

Hello,


//I have the following situation:

//baseclass : Employee

class Employee{

private:
string name;

public :
Employee(string );
void SetName(string) ;
virtual double Earnings();

//********
derived classes: Manager , Salesman
//a Manager gets paid hourly ( a constant Wage),
//a Salesman gets a fixed wage + a Commission

class Manager : public Employee {

private:
int hours;
static double wage;

public:
Manager(string) ;
void getHours(int); // <-----
virtual double Earnings();


/*PROBLEM:

All the managers and salesmen are stored in a STL map
map<int,Employe e> ieMap; in an other class.

When I iterate this map, how can ik call getHours(int) from Manager
(supposed the iterator points to a Manager object,
or is it the whole "point" that the objects Manager and Salesman are stored
as an Employee???? I hope not..).

I tried RTTI, didn't work (probably my fault, but hey, I couldn't do it)

Is there a possibility with Polymorphism??? (and cleaner..)

Hints, tips??

kind regards,
Pieter

ps: sorry for my bad "inglisch"; )


*/

[Victor Bazarov]

Re: Polymorphism

"Pieter" <pieterdm@hotma il.com> wrote...[color=blue]
> //I have the following situation:
>
> //baseclass : Employee
>
> class Employee{
>
> private:
> string name;
>
> public :
> Employee(string );
> void SetName(string) ;
> virtual double Earnings();
>
> //********
> derived classes: Manager , Salesman
> //a Manager gets paid hourly ( a constant Wage),
> //a Salesman gets a fixed wage + a Commission
>
> class Manager : public Employee {
>
> private:
> int hours;
> static double wage;
>
> public:
> Manager(string) ;
> void getHours(int); // <-----
> virtual double Earnings();
>
>
> /*PROBLEM:
>
> All the managers and salesmen are stored in a STL map
> map<int,Employe e> ieMap; in an other class.
>
> When I iterate this map, how can ik call getHours(int) from Manager
> (supposed the iterator points to a Manager object,
> or is it the whole "point" that the objects Manager and Salesman are[/color]
stored[color=blue]
> as an Employee???? I hope not..).[/color]

You cannot. If you store _objects_, you get the situation known in C++
as _slicing_. Every time you get an instance of Manager and try to stuff
it into your map, the Employee part of the Manager gets stored and the
rest gets _sliced__off_.
[color=blue]
>
> I tried RTTI, didn't work (probably my fault, but hey, I couldn't do it)
>
> Is there a possibility with Polymorphism??? (and cleaner..)
>
> Hints, tips??[/color]


You need to store pointers to Employee:

map<int,Employe e*>

but make sure you create your Managers or Salesmen _dynamically_ and
dispose of them properly when you don't need them any longer. Also,
in order to do that, your Employee's destructor _must_ be virtual.

Search Google Groups for "polymorphi sm STL container" for more
information (no double quotes, of course).

Victor

[David White]

Re: Polymorphism

"Victor Bazarov" <v.Abazarov@com Acast.net> wrote in message
news:5pZFb.4354 14$Dw6.1334408@ attbi_s02...[color=blue]
> You need to store pointers to Employee:
>
> map<int,Employe e*>
>
> but make sure you create your Managers or Salesmen _dynamically_ and
> dispose of them properly when you don't need them any longer.[/color]

I agree that for most practical purposes you would have to create the
objects dynamically, but it's not a requirement as far as the map is
concerned. You could do something like this if you wanted:

int main()
{
// create a bunch of automatic Managers and Salesman objects
// (but not in a loop or nested scope)

// create the map

// add the addresses of all Employees to the map

// iterate over the map and do various polymorphic operations
// or pass the map to other functions

} // everything destroyed automatically

I just wanted to make sure the OP didn't misunderstand the reason for
creating the objects dynamically, which is that normally you wouldn't know
what Employee objects you'll need until run-time.

DW

[Cy Edmunds]

Re: Polymorphism

"Pieter" <pieterdm@hotma il.com> wrote in message
news:b4ZFb.9297 2$0l5.4170821@p hobos.telenet-ops.be...[color=blue]
> Hello,
>
>
> //I have the following situation:
>
> //baseclass : Employee
>
> class Employee{
>
> private:
> string name;
>
> public :
> Employee(string );
> void SetName(string) ;
> virtual double Earnings();
>
> //********
> derived classes: Manager , Salesman
> //a Manager gets paid hourly ( a constant Wage),
> //a Salesman gets a fixed wage + a Commission
>
> class Manager : public Employee {
>
> private:
> int hours;
> static double wage;
>
> public:
> Manager(string) ;
> void getHours(int); // <-----
> virtual double Earnings();
>
>
> /*PROBLEM:
>
> All the managers and salesmen are stored in a STL map
> map<int,Employe e> ieMap; in an other class.
>
> When I iterate this map, how can ik call getHours(int) from Manager
> (supposed the iterator points to a Manager object,
> or is it the whole "point" that the objects Manager and Salesman are[/color]
stored[color=blue]
> as an Employee???? I hope not..).
>
> I tried RTTI, didn't work (probably my fault, but hey, I couldn't do it)
>
> Is there a possibility with Polymorphism??? (and cleaner..)
>
> Hints, tips??
>
> kind regards,
> Pieter
>
> ps: sorry for my bad "inglisch"; )
>
>
> */[/color]

See the thread:

HELP: vector & polymorphism

The situation with std::map is the same.

Newsgroup: Can we PLEASE get this into the FAQ? It's bad enough that the
standard library support for polymorphism is so thin -- the workarounds need
to be documented.

--
Cy

http://home.rochester.rr.com/cyhome/