Template classes

Waldermort

I have defined a template class in a header file like so:

template <class _T> class TCollection {
public:
TCollection();
~TCollection();

Then try to declare the members in the cpp file like so:

TCollection::TCollection() : pData(0) , pCount(0)
{
}

TCollection::~TCollection()
{
clear();
}

Yet I am getting a compiler error 'TCollection' : use of class template requires template argument list Obviously it cannot be treated like a normal class, so what is the correct way of declaring the members?

toxcct

waldermort wrote:

template class TCollection

BTW, what is pData declared like ?

TOXCCT >>> GEII power

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prasad_som

Probably problem is you have used TCollection class object without using argument list. You need to use it like this,

TCollection<int> objTCollection;

Prasad Notifier using ATL

Waldermort

TCollection<class _T>::TCollection() That worked, thankyou.

Waldermort

I tell a lie, it worked for the c'tor and d'tor but not the other members. This is the header file:

template <class _T> class TCollection {
public:
TCollection();
~TCollection();
_T at(unsigned int iPos);
void add(_T T);
void clear();
int size();
bool empty();
private:
_T* pData;
int pCount;
};

And the cpp file looks something like this:

TCollection<class _T>::TCollection() : pData(0) , pCount(0)
{
}

TCollection<class _T>::~TCollection()
{
clear();
}

_T TCollection<class _T>::at(unsigned int iPos)
{
if (iPos >= 0 && iPos > pCount)
return pData[iPos];
else
return NULL;
}

void TCollection<class _T>::add(_T T)
{
if (pData) {
_T *tmp = new _T [pCount+1];
for (int i=0;i<pCount;i++)
tmp[i] = pData[i];
tmp[i] = T;
delete [] pData;
pData = tmp;
pCount++;
} else {
pData = new _T [1];
pData[0] = T;
pCount++;
}
}

I'm getting error like E:\Program\foo\TCollection.cpp(18) : error C2027: use of undefined type '_T' E:\Program\foo\TCollection.cpp(8) : see declaration of '_T' E:\Program\foo\TCollection.cpp(20) : error C2036: 'class _T *' : unknown size E:\Program\foo\TCollection.cpp(28) : error C2512: '_T' : no appropriate default constructor available This is only after a split it into seperate files, it worked in a single file.

toxcct

template<class _T>
_T TCollection::at(unsigned int iPos){...}

template<class _T>
void TCollection::add(_T T){...}

TOXCCT >>> GEII power

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Waldermort

Thanks for your help with this, but I am still getting errors.

template<class _T> _T TCollection::at(unsigned int iPos)
{
...
}

template<class _T> void TCollection::add(_T T)

Results in the first error: E:\Program\foo\TCollection.cpp(17) : error C2955: 'TCollection' : use of class template requires template argument list e:\program\foo\tcollection.h(24) : see declaration of 'TCollection' E:\Program\foo\TCollection.cpp(25) : error C2955: 'TCollection' : use of class template requires template argument list

toxcct

template<class _T>
_T TCollection**<_T>**::at(unsigned int iPos){...}

template<class _T>
void TCollection**<_T>**::add(_T T) {...}

TOXCCT >>> GEII power

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Waldermort

Thankyou that worked, but now having problems with the pData pointer. I thought it would be easy to use seperate files. Rather than messing about I have placed the whole thing in the single header file, it's only a small class.

toxcct

template classes inmplementations have to be in the header... what is the problem with pData exactly ?

TOXCCT >>> GEII power

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Waldermort

I can't remember eaxactly after putting it back in the header, it was something about an unknown class size when trying to delete it. Basicaly this is just a template similar to the vector class, with the exception it's smaller and calls the destructor.

Anonymuos

waldermort wrote:

I have defined a template class in a header file like so:

It's a class template, not a template class.

waldermort wrote:

Then try to declare the members in the cpp file like so:

You cannot define template members in a cpp file. Look up the C++ FAQ!

MayankT

When defining you must explicitly declare the function as template: template <class _T> TCollection<_T>::TCollection () : pData(0), pCount(0) { } template <class _T> TCollection<_T>::~TCollection () { clear(); }

---------------------- Mayank Thakore Learning C++ - since 1998 They didn't print my card right; so I resigned.

Waldermort

Well I do appologise if my English offends you, although it appears the other members (forum members that is and not class members before you get confused) here did not have such a hard time understanding me. May I ask, Mr.Anonymuos, do you use the same attitude when your customers come to you with a problem?

toxcct

well, you're right. indeed, i think i already answered him (if you read the previous posts...)

TOXCCT >>> GEII power

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Zac Howland

toxcct wrote:

template classes inmplementations have to be in the header.

This is only because there is no compiler out there that meets this part of the standard (mainly due to the insane complexity it takes to accomplish it). The standard allows for placing template definitions in header files and implementations in cpp files. To get around this problem, I generally either put the entire class definition and implementation into a single file, or I place a #include "myclass.cpp" at the bottom of my header file.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week Zac

toxcct

yes i know that, but that fact is that actually, so i didn't want to pollute the post with something that wouldn't have helped...

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Michael Dunn

Separating template classes into .h and .cpp files is too much of a headache when you're just starting out with templates. It's far easier to put everything in the .h file. See the C++ FAQ Lite[^] template section for more details.

--Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ