I am using VC++ 2005. I have a class template located in the file "SchemaParser.h" which defines a static member:

template <typename _alloc>
class SchemaParser
{
protected:
    static SaxBaseNoTemp* rootNode;
};

Then I define the static variable in "SchemaParser.cpp":

#include "SchemaParser.h"

template<typename _alloc> smiXML::SaxBaseNoTemp* smiXML::SchemaParser<_alloc>::rootNode = 0;

But when I include and use SchemaParser in main.cpp, I get the following message: error LNK2001: unresolved external symbol "protected: static class smiXML::SaxBaseNoTemp * smiXML::SchemaParser<class DAll>::rootNode" I suspect it has something to do with the compiler having to make copies of the template, but I haven't found anything on Google to confirm this. I've only found the suggestion that I define a static in the header's corresponding source file. If I move the definition of rootNode to the bottom of SchemaParser.h, it works fine. Does anyone know why this is happening? And why is it giving me a linker error when I define rootNode in SchemaParser.cpp? EDIT: To clarify, I am placing the same line

template<typename _alloc> smiXML::SaxBaseNoTemp* smiXML::SchemaParser<_alloc>::rootNode = 0;

in two different places, and only one (in SchemaParser.cpp) gives me a linker error. What has me perplexed is that only one of them works. [Edited by - Guru2012 on May 20, 2006 3:03:09 AM]

Yes, if it really comes down to doing it your way, I definitely will as it seems to be of minimal hassle. I'm just hoping there's a more "generic" way to do it.

Template classes are a bit different than normal classes. In the case of static variables u either need to intialize them in the class definition itself, or outside the class but still in the header file (not in a separate C file).

For example:

template <typename T> class Bob {

static const int i = 0;

};


or you could do:

template <typename T> class Bob {

static int i;

};

template<typename T> int Bob<T>::i = 0;


But in either case it must be in the header file. Why? Well a template class isn't actaully a class its mearly a template that the compiler uses to build a class. So it needs the whole template to build the class properly. It seems in your case the lack of a proper static variable definition caused the linker error. Also it seems u have given it an explicit specialization, whereas the code above is a generic specialization (ehh, I hope I didn't butcher the terminology).