I wrote a class which take two components, an random class type T and an integer, I implement it like following: In Test.h like:

    template <class A, int B>class Test { // two components, 
    private: 
        A first;
        int second;

    public:
        Test();
        Test (A,int);
    }

In Test.cpp I did:

    template <class T,int i> Test<T,i>::Test() {}
    template <class A,int i>Test<A,i>::Test(T a, int b):first(a) {second=b;}

But in Main function:

    Test<int, int >  T1; //It can not be passed
    Test<int, 4> T2; //It can not be passed 
    int x = 8;
    Test<int, x> T3 (3,4);// can not be passed

How I can declare an object instance from the above generic class?

• c++

You forgot the semicolon at the end of the class template definition.

template <class T,int i> Test<T,i>::Test() {}
template <class A,int i>Test<A,i>::Test(T a, int b):first(a) {second=b;}

You need to put these two template function definitions in the header rather than the .cpp - the actual code needs to be made available to all compilation units that call these functions, not just the declaration.

Test<int, int >  T1; //It can not be passed

This is invalid, the second int is a type, but the template expects an int value

Test<int, 4> T2; //It can not be passed 

There's nothing wrong with this

int x = 8;
Test<int, x> T3 (3,4);// can not be passed

You need to make the first of these lines static const x = 8 (i.e. make x a compile-time constant) to make it a usable as a template parameter

And there's also the missing semicolon at the end of the class definition.