Introducing a Template as a parametre of another Template

[Ruben]

Hi,

I'm trying to define a library which needs an undefined parametre to be passed as a template parametre. This is my code (sumarized):


template <typename V> struct INFO_ELEMENT
{
unsigned char TYPE[4];
unsigned char *LENGTH;
V *VALUE;

public:
INFO_ELEMENT(unsigned int L);

};

template <class V> INFO_ELEMENT<V>::INFO_ELEMENT(unsigned int L)
{
*LENGTH = new unsigned char[1];
LENGTH = (unsigned char)L;
*VALUE = new V[L];

}

template <typename T> struct LIST
{
unsigned char *Length;
T *Value;

public:
LIST(unsigned int L);

};

template <class T> LIST<T>::LIST(unsigned int L)
{
*Length = new unsigned char[1];
Length = (unsigned char)L;
*Value = new T[L];
/*...*/

}

typedef LIST<INFO_ELEMENT>* IR_BIN_DATA;


The error occurs at the last line, where the parametre INFO_ELEMENT passed as the parametre of the instantiation of the class LIST is forbidden. Is is because it expects a type instead of a template.Does anybody know how to solve this issue?

Thanks!

[jsmith]

INFO_ELEMENT is itself a template. Your typedef did not specify the template parameter of INFO_ELEMENT.

typedef LIST<INFO_ELEMENT<int> >* IR_BIN_DATA;

works for example.

[Ruben]

Yes,

I knew it worked, but I left it blank this way "typedef LIST<INFO_ELEMENT>* IR_BIN_DATA;" because I wanted to encapsulate a generic data type. Is it possible? How could I do it?

Thanks!

[jsmith]

Unfortunately you can't do that with a typedef.

[Ruben]

So, is there any other possibility? with or without typedef? anything similar (or not)? any idea?

Thanks!

[jsmith]

What about this? Does this work?

template< class T > 
class IR_BIN_DATA : public LIST< INFO_ELEMENT< T > >
{ 
   public:
       explicit IR_BIN_DATA( unsigned L ) : 
           LIST< INFO_ELEMENT<T> >( L ) {}
};

[Ruben]

Thank you jsmith! that's almost what I wanted. I didn't know I could implement it that way.

Thanks a lot!