Array of templated structure

I have problem defining array of a templated structure

Firstly there is one .h file which consists of a template class,all the definitions of functions are defined in this class itself because its a template class.

Code:

//test.h
template<Data_T>
class test
{
test test_func_1(const test &var);
.....
}

There is another header file which has a structure "example" which should have a fucntion pointer as mentioned below,As "test" class is a template class i want this function pointer "fun_ptr" to behave like that

Code:

//test2.h
i can declare this structure like this (only one version,int only)  

1. struct example
	{
	int a
	float b
	test<int> (*fun_ptr)(const test &a);
	}

     OR

2.   template<typename Data_T>
 	 struct example
	{
	int a
	float b
	test<Data_T> (*fun_ptr)(const test &a);
	}

both of these version compiles successfully.

Now i want to declare an array of this templated structure e.g.

Code:

example example_array[]
{
 {1,2,test_func_1},  //test_func_1 is defined in test.h file
 {3,4,test_func_2},  //test_func_2 is defined in test.h file
};

But compiler gives an error at this point. If i use "template<typename Data_T>" before "example_array[]" then also compiler gives error.
Please tell me how to achieve this. Because of templates it is giving me errors.

My guess is that fun_ptr is supposed to be a member function pointer instead. I got it to work with:

Code:

template<typename Data_T>
class test
{
public:
    test test_func_1(const test &var)
    {
        return var;
    }

    test test_func_2(const test &var)
    {
        return var;
    }
};

template<typename Data_T>
struct example
{
    example(int a, float b, test<Data_T> (test<Data_T>::*fun_ptr)(const test<Data_T> &a))
        : a(a), b(b), fun_ptr(fun_ptr) {}

    int a;
    float b;
    test<Data_T> (test<Data_T>::*fun_ptr)(const test<Data_T> &a);
};

int main()
{
    example<int> example_array[] =
    {
        example<int>(1, 2, &test<int>::test_func_1),
        example<int>(3, 4, &test<int>::test_func_2),
    };
}

Yeah,your guess is right. It is a member function. But instead of declaring the "example_array[]" in main i want this array to be statically initialized. Because filling this array in main loop restrict it to the <int> as in example given by you.

Originally Posted by cplusplustudent

But instead of declaring the "example_array[]" in main i want this array to be statically initialized. Because filling this array in main loop restrict it to the <int> as in example given by you.

What do you mean? It will still be an array of example<int> or whatever other type you want whether it has static storage duration or not.

I got your point. I can not declare it without giving any type as compiler needs to reserve the memory for array and it needs to know for which type. This is my understanding.

I am not able to compile the code. As it says that "incomplete type ... used in nested name specifier". I suppose compiler is complaining because it needs the full definition of "test" class.
But test is present in test.h file,which is a template file(having all the definition of templated member functions of test class), example is in different file test2.h.
I can not include test.h in test2.h as compiler is again complaining.

This does not give us a lot of information as to what is wrong. I suggest you post an example.

I created a small project and listing out the files below

//test.h

Code:

#include <iostream>


template<typename Data_T>
class test
{
public:
	test test_func_1(const Data_T &var);
};

template<typename Data_T >
test test<Data_T>::test_func_1(const Data_T &var)
{
		std::cout << "test_func_1: " << var << std::endl;
}

//test2.h

Code:

#include <iostream>
#include <test.h>


template<typename Data_T> class test;



template<typename Data_T>
struct example
{
	int a;
	float b;
	test<Data_T> (test<Data_T>::*fun_ptr)(const Data_T& a);
};


example<int> example_array[] =
{
	{1, 2, &test<int>::test_func_1},
	{1, 2, &test<int>::test_func_1},
};

//main.cpp

Code:

#include <iostream>
#include <test2.h>

int main()
{
	std::cout<<"test_func"<<example_array[0].a<<std::endl;
	
}

I can not include test.h file in test2.h file because if i do so then it gives error at

Code:

template<typename Data_T >
test test<Data_T>::test_func_1(const Data_T &var) //error: expected constructor, destructor, or type conversion before ‘test’
{
		std::cout << "test_func_1: " << var << std::endl;
}

You should include test.h. You have a simple typo:

Code:

test<Data_T> test<Data_T>::test_func_1(const Data_T &var)