Call object's method within template

Question

I have following code:

template<class T>
class TemplateA  : public virtual std::list<T>
{
protected:
    unsigned int iSize;
public:
    unsigned int getSize();
};
/////////////
template<class T>
unsigned int TemplateA<T>::getSize()
{
    return iSize;
}
/////////////
/////////////
/////////////
template<class T>
class TemplateB : public TemplateA<T>
{
public:
    unsigned int calcSize();
};
/////////////
template<class C>
unsigned int TemplateB<C>::calcSize()
{
    iSize = C.getSize;
    return iSize;
}
/////////////
/////////////
/////////////
// Class C (seperate file) has to contain function getSize()
class CMyClass
{
public:
    static const unsigned int getSize = 5;
};

This means, within class TemplateB I want to call the getSize method, which the passed class have defined.

I receive the following error message:

error C2275: 'C' : illegal use of this type as an expression
while compiling class template member function 'unsigned int TemplateB<C>::calcSize()'
1>          with
1>          [
1>              C=CMyClass
1>          ]

I'm quiet sure that this function worked under VS 2003... What's wrong with the method? Maybe a compiler setting? I don't know where to set what :(

Answer 1

You should say this->getSize or C::getSize; this will defer lookup to the second phase when the template arguments are known.

Answer 2

Hi you could simplify your code too whilst correcting, all you seem to have done is use C rather than TemplateB so if you do:

template<class C>
unsigned int TemplateB<C>::calcSize()
{
    return  c::getSize; //based on getSize being static
}

You will save the memory of an extra variable and it should work fine:)

Addendum: Here is a working code snippet using your code as a basis:

#include <iostream>
#include <list>

using namespace std;

template<class T>
class TemplateA  : public virtual std::list<T>
{
protected:
    unsigned int iSize;
public:
    unsigned int getSize();
};

template<class T>
unsigned int TemplateA<T>::getSize()
{
    return iSize;
}

template<class T>
class TemplateB : public TemplateA<T>
{
public:
    unsigned int calcSize();
};

template<class C>
unsigned int TemplateB<C>::calcSize()
{
    return C::getSize;
}

// Class C (seperate file) has to contain function getSize()
class CMyClass
{
public:
    static const unsigned int getSize = 5;
};
int main()
{
    CMyClass classme;
    TemplateB<CMyClass> test ;
    cout <<"Calc size outputs: "<< test.calcSize() << endl;

   return 0;
}

Apologies for the unchecked answer previously. Hope this one helps!