Hello Experts!

I have been playing around a bit with this multiple inheritance and I wonder
why do I get a compile error
if I remove the virtual keyvord from the declaration of the Student class
and the Employee class.
I have removed all kind of data from all classes.
The compile error occur when I instansiate Person* p = new
TeachingAssistent;
The error I get is c:\Documents and
Settings\Tony\kau\cplusplus\test4\start.cpp(8): error C2594: 'initializing'
: ambiguous conversions from 'TeachingAssistent *' to 'Person *'

I know that if I have some data in the virtual base klass and not using the
virtual keyword I would get compile error because of having double defined
data in the TeachingAssistent() but I understand why so that's is no
problem.


#include <string>
using namespace std;

class Person
{
public:
Person() {}
string getName() const
{
return "rulle";
}
};

class Student : public Person
{
public:
Student() {}
};

class Employee : public Person
{
public:
Employee() {}
};

class TeachingAssistent : public Student, public Employee
{
public:
TeachingAssistent() {}
};

class GraduateAssistent : public TeachingAssistent
{
};

int main()
{
Person* p = new TeachingAssistent;
cout << p->getName() << endl;
}

Tony Johansson wrote:[color=blue]
> I have been playing around a bit with this multiple inheritance and I
> wonder why do I get a compile error
> if I remove the virtual keyvord from the declaration of the Student
> class and the Employee class.
> I have removed all kind of data from all classes.
> The compile error occur when I instansiate Person* p = new
> TeachingAssistent;
> The error I get is c:\Documents and
> Settings\Tony\kau\cplusplus\test4\start.cpp(8): error C2594:
> 'initializing'[color=green]
>> ambiguous conversions from 'TeachingAssistent *' to 'Person *'[/color]
>
> I know that if I have some data in the virtual base klass and not
> using the virtual keyword[/color]

How could you have a virtual base class without using 'virtual' keyword?
[color=blue]
> I would get compile error because of having
> double defined data in the TeachingAssistent() but I understand why
> so that's is no problem.[/color]

Since your 'TeachingAssistent' (BTW, in English it's spelled slightly
differently: 'TeachingAssistant') has _two_ copies of 'Person' class,
one from 'Student', and the other from 'Employee', the compiler cannot
decide to which 'Person' to convert the pointer to 'TeachingAssistent'.

[color=blue]
> #include <string>
> using namespace std;
>
> class Person
> {
> public:
> Person() {}
> string getName() const
> {
> return "rulle";
> }
> };
>
> class Student : public Person
> {
> public:
> Student() {}
> };
>
> class Employee : public Person
> {
> public:
> Employee() {}
> };
>
> class TeachingAssistent : public Student, public Employee
> {
> public:
> TeachingAssistent() {}
> };
>
> class GraduateAssistent : public TeachingAssistent
> {
> };
>
> int main()
> {
> Person* p = new TeachingAssistent;
> cout << p->getName() << endl;
> }[/color]

V

Tony Johansson wrote:[color=blue]
> Hello Experts!
>
> I have been playing around a bit with this multiple inheritance and I wonder
> why do I get a compile error
> if I remove the virtual keyvord from the declaration of the Student class
> and the Employee class.
> I have removed all kind of data from all classes.
> The compile error occur when I instansiate Person* p = new
> TeachingAssistent;
> The error I get is c:\Documents and
> Settings\Tony\kau\cplusplus\test4\start.cpp(8): error C2594: 'initializing'
> : ambiguous conversions from 'TeachingAssistent *' to 'Person *'
>[/color]
For more information take a look at virtual base class documentation.
For the time-being you can fix the problem
as shown below[color=blue]
>
>
> class Student : public Person[/color]
change to class Student : virtual public person[color=blue]
>
> class Employee : public Person[/color]
change to class Employee : virtual public person