Template Inheritance Problem

[jayesah@gmail.com]

I have following code:

#include <iostream>
using namespace std;

template <class Tclass Parent
{
public:
void fun(const T a){ }
};

class myclass: public Parent<int*>
{
public:
void myclassfun(cons t int* a)
{
Parent<int*>::f un(a);
}
};
int main() {
myclass obj1;
int * ptr;
obj1.myclassfun (ptr);
return 0;
}

This gives me compilation error:
"In member function `void myclass::myclas sfun(const int*)':
error: invalid conversion from `const int*' to `int*'
error: initializing argument 1 of `void Parent<T>::fun( T) [with T =
int*]' "

Please tell me what is the problem here ?
I am not allowed to change Parent class interface.

Jayesh

[Ian Collins]

Re: Template Inheritance Problem

jayesah@gmail.c om wrote:

I have following code:
>
#include <iostream>
using namespace std;
>
template <class Tclass Parent
{
public:
void fun(const T a){ }
};
>
class myclass: public Parent<int*>
{
public:
void myclassfun(cons t int* a)
{
Parent<int*>::f un(a);

just write fun(a);

}
};
int main() {
myclass obj1;
int * ptr;
obj1.myclassfun (ptr);
return 0;
}
>
This gives me compilation error:
"In member function `void myclass::myclas sfun(const int*)':
error: invalid conversion from `const int*' to `int*'
error: initializing argument 1 of `void Parent<T>::fun( T) [with T =
int*]' "
>
Please tell me what is the problem here ?

Nothing to do with templates, you are passing a pointer to const int to
a function that expects a const int pointer. The two are different
types, the former is a mutable pointer to an immutable object, the
latter is an immutable pointer to a mutable objects.

--
Ian Collins.

[h.yuzhao@gmail.com]

Re: Template Inheritance Problem


"Ian Collins дµÀ£º
"

jayesah@gmail.c om wrote:

I have following code:

#include <iostream>
using namespace std;

template <class Tclass Parent
{
public:
void fun(const T a){ }
};

class myclass: public Parent<int*>
{
public:
void myclassfun(cons t int* a)
{
Parent<int*>::f un(a);

>
just write fun(a);
>

}
};
int main() {
myclass obj1;
int * ptr;
obj1.myclassfun (ptr);
return 0;
}

This gives me compilation error:
"In member function `void myclass::myclas sfun(const int*)':
error: invalid conversion from `const int*' to `int*'
error: initializing argument 1 of `void Parent<T>::fun( T) [with T =
int*]' "

Please tell me what is the problem here ?

>
Nothing to do with templates, you are passing a pointer to const int to
a function that expects a const int pointer. The two are different
types, the former is a mutable pointer to an immutable object, the
latter is an immutable pointer to a mutable objects.
>
--
Ian Collins.

No, I can't exactly agree with you...:)
I think this was caused by that int* and const int* are not the same.
Immutable pointer to int is declared as int* const p; but immutable int
of pointer shoud be const int* p.

[Ian Collins]

Re: Template Inheritance Problem

h.yuzhao@gmail. com wrote:

"Ian Collins дµÀ£º

>>
>>Nothing to do with templates, you are passing a pointer to const int to
>>a function that expects a const int pointer. The two are different
>>types, the former is a mutable pointer to an immutable object, the
>>latter is an immutable pointer to a mutable objects.
>>

>
No, I can't exactly agree with you...:)
I think this was caused by that int* and const int* are not the same.
Immutable pointer to int is declared as int* const p; but immutable int
of pointer shoud be const int* p.
>

Sorry, but the function sig was void fun(const T a) which instantiates
to int* const, a constant pointer, not a pointer to const.

--
Ian Collins.