Expected template-name before ‘<’ token.Template class inheritance and virtual method

[famat]

Hi all,
I have C++ source code that compiles on windows-MS VS2005 without any problem. I am trying to compile it in Linux gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4) and I ran into the following compiler error:

error: expected template-name before ‘<’ token
error: expected `{' before ‘<’ token
error: expected unqualified-id before ‘<’ token

(the error points to the line containing class myMarchingSurface3D:public CMarchingSurface3D<U> in the derived class)

I have looked in other threads and it seems inheritance with template classes gives some portability problems. I attach the code here:

template<class U> 
class CMarchingSurface3D
{
   [...other methods]
public:
  inline virtual CVector3D<TV3DFLOAT> GetVoteDir(CPoint3D<INT16> &p, CTokenGroup3D<U>& tokengroup) { return CVector3D<TV3DFLOAT>(0,0,0); }
 
}
 
// implement the virtual functions here for
    // marching surface.
class myMarchingSurface3D:public CMarchingSurface3D<U>{
    public:
 
      [...othe rmethods]
        inline CVector3D<TV3DFLOAT> GetVoteDir(CPoint3D<INT16>& p, CTokenGroup3D<U>& tokengroup) {
            //collect the the stick vote from neighbour
            CTensorVote3D<TV3DFLOAT> vote=
                m_kernal->GetAllStickVotesTensor(p,tokengroup,*m_stickfield);
            vote.Split();
            // we use the sqrt(Lambda1)-sqrt(Lambda2) for voxel strength
            m_lastSal=sqrt(vote.GetLambda1())-sqrt(vote.GetLambda2());
            return vote.GetE1();
        }
    };

Thanks for your help in advance,
Fernando

[weaknessforcats]

class myMarchingSurface3D:public CMarchingSurface3D<U>{
public:

[...othe rmethods]

You need to declare this class as a template to support inheriting from CMarchingSurface3D<U>. Otherwise, the compiler thinks U is a real type:

template <class U>
class myMarchingSurface3D:public CMarchingSurface3D<U>{
public:
 
[...othe rmethods]
 

Also, there are no inline virtual functions. Virtual functions have their addresses kept in a virtual function table (VTBL) to support polymorphism.

Inline functions are merely copied inline where they are called. They don't have addresses. Since C++ sees the inline keyword as a suggestion by you, it doesn't necessarily have to agree to it. In this case, the inline is ignored in favor of the virtual keyword.

Personally, I would remove the inline keyword from the templates.

[famat]

You need to declare this class as a template to support inheriting from CMarchingSurface3D<U>. Otherwise, the compiler thinks U is a real type:

template <class U>
class myMarchingSurface3D:public CMarchingSurface3D<U>{
public:
 
[...othe rmethods]
 

Also, there are no inline virtual functions. Virtual functions have their addresses kept in a virtual function table (VTBL) to support polymorphism.

Inline functions are merely copied inline where they are called. They don't have addresses. Since C++ sees the inline keyword as a suggestion by you, it doesn't necessarily have to agree to it. In this case, the inline is ignored in favor of the virtual keyword.

Personally, I would remove the inline keyword from the templates.

Hi,
Thanks for the quick reply and the tips. I added template<class U> as suggested but I still get the same error from the gcc compiler. Any idea what can be the problem?

Thanks,
Fernando

[weaknessforcats]

No. I got it to compile using Visual Studio.NET 2005. I know very little about gcc. I assume you are compiling as g++ to get the C++ compiler?

[famat]

No. I got it to compile using Visual Studio.NET 2005. I know very little about gcc. I assume you are compiling as g++ to get the C++ compiler?

Hi,
Yes, I am using g++. The problem seems to be somehow with the standards. As I said in my first post I compile without any problem using MS-VS. However, GNU gcc wants things different. But after trying many different things I don't know how to put them different. Any suggestion?

Thanks,
Fernando

[Laharl]

I fixed a similar problem by templating with

template<typename U>
class A {
 

Using typename rather than class or classname seems to make g++ happier for some reason...

[famat]

I fixed a similar problem by templating with

template<typename U>
class A {
 

Using typename rather than class or classname seems to make g++ happier for some reason...

Hi,
Where do I have to change template<class U> by template<typename U>? Everywhere (in all the .cpp implementing the methods for teh template class?)? What is the difference between typename and class?

I tried to change class U by typename U only in the declaration and teh compiler still gives the same error.

Thanks,
Fernando

[Laharl]

Everywhere you have template<class U>, change it to template<typename U>.

I can't guarantee this will work, but I've had success with it, as the book I learned from used <classname U> and that gave me errors until I switched to typename.

[famat]

Everywhere you have template<class U>, change it to template<typename U>.

I can't guarantee this will work, but I've had success with it, as the book I learned from used <classname U> and that gave me errors until I switched to typename.

Hi,
I tried to change it everywhere and still gives the same error. However, the code compiles with gcc-3.3.5 (I just tried it) but not with gcc-4.1.2. Any idea what happens? This is very frustrating:(

Thanks,
Fernando

[Laharl]

Frankly, I can't tell you any more, though I have had some issues with templates on later versions of gcc.

[weaknessforcats]

Everywhere you have template<class U>, change it to template<typename U>.

I can't guarantee this will work, but I've had success with it, as the book I learned from used <classname U> and that gave me errors until I switched to typename.

class U and typename U are equivalent. typename is generally used by template writers whio are not using classes.

There is no such thing as classname. That is a synrtax error.

On g++, has anyone tried the -pedantic switch? That disables non-ANSI extensions to C++.