template error.

[mylea]

I wrote a template class named "Class3". i also define a class "CNode" in class "Class3". all these code are written in file "mytemplate.h". when compiled, errors happens, just like:
testTemplate.obj : error LNK2001: unresolved external symbol "public: __thiscall Class3<int>::CNode::CNode(class Class3<int>::CNode *)" (??0CNode@?$Class3@H@@QAE@PAV01@@Z)
testTemplate.obj : error LNK2001: unresolved external symbol "public: __thiscall Class3<int>::CNode::~CNode(void)" (??1CNode@?$Class3@H@@QAE@XZ)
Debug/testTemplate.exe : fatal error LNK1120: 2 unresolved externals
Error executing link.exe.

but when put constructor define of class "CNode" ,inside of declare of class "Class3",there are no errors. why?
template <class TYPE>
class Class3 : public CObject
{
public:
Class3();// Construction
virtual ~Class3();

class CNode
{
public:
CNode(CNode* pNodeParrent = NULL);
~CNode();
CNode* pParent;
CNode* pChild[10];
TYPE data;
};
};

template <class TYPE>
Class3<TYPE>::Class3()
{

}

template<class TYPE>
Class3<TYPE>::~Class3()
{


}

template<class TYPE>
Class3<TYPE>::CNode::CNode(CNode* pNodeParrent)
{
pParent = pNodeParrent;
for( int i=0; i<10; ++i) {
pChild[i] = NULL;
}
ZeroMemory(&data, sizeof(TYPE));

}
template<class TYPE>
Class3<TYPE>::CNode::~CNode()
{
pParent = NULL;
for( int i=0; i<10; ++i)
if( pChild[i]) {
delete pChild[i];
pChild[i] = NULL;
}

};