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Template Classes

Started by NuffSaid Oct 7, 2001 at 3:35 PM 6 replies 400+ views

Original Post

Oct 7, 2001 at 3:35 PM

I''m having trouble with template classes under MSVC++. I seem to have to declare and define all the member functions of the class in the header file if I''m going to use templates. Is there something I''m doing wrong?

  
template <class T>
class A
{
protected:
  T *data;
public:
  A() : data(NULL){/*Do nothing*/}
  virtual ~A(){}
  void setData(T *newData);//I have to define this in the class

                           //definition and I can''t do this in a 

                           //.cpp file.

};

And another thing. A template class that compiles fine on MSVC++ doesn''t compile at all on g++. Is there some specific switch that I must use or does g++ not support templates well (I remember reading somewhere...).

Icarus3

Oct 7, 2001 at 3:48 PM

If you want to use it in the cpp file you have to do this:

      

//  In the header


template <class T>
class A
{
protected:  
    T *data;
public:  
    A() : data(NULL) {/*Do nothing*/}  
    virtual ~A(){}  
    void setData(T *newData); 
};

         
//  in the cpp file

#include "blaat.h"

template <class T>
A::setData(T* newData)
{
........
}

So for every function you want to implement you have to put template above it

Edited by - Icarus3 on October 7, 2001 4:52:14 PM

NuffSaid

Author

NuffSaid

Oct 7, 2001 at 3:59 PM

I''ve tried what you showed. It doesn''t work. I get compiler errors.

Here are some of the stuff I''ve done

  
//in the cpp file


//1. Doesn''t work

template <class T>
void A::setData(T *data)
{
}


//2. Doesn''t work either

template <class T>
void A<T>::setData(T *data)
{
}


//3. Doesn''t work and I was getting desperate :)

template <class T>
void A<T>::setData<T>(T *data)
{
}

Dactylos

Oct 7, 2001 at 4:14 PM

The reason it doesn''t work is because MSVC++ can''t handle separately compiled templates. That''s why you have to specify the function/method bodies in the header-files.

GCC/g++ generally has better template support than MSVC++ (unless you''re using a really old version of g++), IIRC g++ can even compile templates separately.

NuffSaid

Author

NuffSaid

Oct 7, 2001 at 4:19 PM

So, it is MSVC++''s fault then. Crummy compiler. Wonder if the new version fixes it....

p.s. No, I''m not switching to Borland just to get templates to work. Just a personal opinion but I dislike the interface.

donbonifacio

Oct 7, 2001 at 4:22 PM

you can not define template classes in cpp files, all template classes must be defined inline!!!
if you wanto to check, try opening the STL dir, you will see that there is no cpp...

g++ compiles templates well, VC++ don''t! there are many problems in VC++ because they didn''t went standard there... if you can not compile a template under g++, maybe there''s some parameters missing when you call the g++ (..) what do you write to compile?

about your code, you will have to do this:

template
class A{
protected:
T *data;
public:
A() : data(NULL){/*Do nothing*/}
virtual ~A(){}
void setData(T*newData);
};

template
void A::setData( T *data )
{
/* your code here */
}

Shannon Barber

Mod

368

Shannon Barber

Oct 7, 2001 at 9:17 PM

The only thing I''ve heard of that MSVC6 doesn''t support is partial template specialization.

Anyway, templates have to be defined inlined. They don''t produce any compilable code until you use them on something. I generally put template classes in a .hpp file; the MS STL files just don''t have an extention.

Magmai Kai Holmlor
- Not For Rent

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