Class object help!

[alex067]

I have an assignment where I have to create a template class, create 2 objects one which takes 10 integers and sorts them, and the other which takes 10 strings and sorts them.

I have 2 questions which need to be addressed:

1) There is a big error when compiling, the syntax error states:

// error LNK1120: 2 unresolved externals

// error LNK2019: unresolved external symbol "public: __thiscall TWO<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,10>::~TWO<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,10>(void)" (??1?$TWO@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@$09@@QAE@XZ) referenced in function _main

// error LNK2019: unresolved external symbol "public: __thiscall TWO<int,10>::~TWO<int,10>(void)" (??1?$TWO@H$09@@QAE@XZ) referenced in function _main


2) Since I am using a template, how do I define the member prototype? In other words, instead of declaring the members in the class, I need to define them as function prototypes such as:

public: void ReadData();

void TWO :: ReadData() //this is incorrect apparently, why?


Here is my program:

#include <iostream>
#include <string>
#include <algorithm>

using namespace std;

template <class T, int n>
class TWO
{
private: T a[n];
public:
	void ReadData() //reads data into array a
	{
		for (int i = 0; i < n; i++)
		{
			cin >> a[i];
		}

	}
	void DisplayData() //display the array
	{
		for (int i = 0; i < n; i++)
		{
			cout << a[i] << " ";
		}
		cout << endl;
	}
	void SortArray() //sort the array
	{
		sort(a, a + 10);
		for (int i = 0; i < n; i++)
		{
			cout << a[i] << " ";
		}
		cout << endl;
	}
	~TWO(); //clean up object
};

int main()
{
	TWO <int, 10> P;
	TWO <string, 10> Q;

	cout << "Enter 10 integers for object P: " << endl;
	P.ReadData(); //reads 10 data from user

	cout << "Enter 10 strings for object Q: " << endl;
	Q.ReadData(); //reads 10 string data from user

	cout << "The entry for object P is: " << endl;
	P.DisplayData(); //display the data

	cout << "The entry for object Q is: " << endl;
	Q.DisplayData(); //display the data

	cout << "The sorted array for object P: " << endl;
	P.SortArray(); //display sorted int data

	cout << "The sorted array for object Q: " << endl;
	Q.SortArray(); //display sorted string data


	system("PAUSE");
	return 0;

}

[shadowCODE]

problem 1:
// error LNK1120: 2 unresolved externals means you are calling a function which is not defined.
That is the destructor in line 37. Do ~TWO(){}.

problem 2:

template<class T>
class MyClass
{
    void fx1();  //for a class template, its member functions are also template functions
    void fx2();
};

//to define the fuctions declared above:

 //we are no longer in the scope of the class, so we need a separate
//template argument for each function.

template<class T> 
void MyClass:: fx1() {}

template<classT>
void MyClass::fx2(){}

Besides these, your program just has problem 1

[alex067]

Ah, I see. thank you so much shadow!

[alex067]

I am now receiving an error for each function header stating that it does not match an existing function.

template <class T, int n>
class TWO
{
private: T a[n];
public:
	void ReadData(); //reads data into array a
	void DisplayData(); //display the array
	void SortArray(); //sort the array
	~TWO(); //clean up object
};

template <class T, int n>
void TWO::ReadData()
{
	for (int i = 0; i < n; i++)
		{
			cin >> a[i];
		}
	
}

template <class T, int n>
void TWO::DisplayData()
{
	for (int i = 0; i < n; i++)
	{
		cout << a[i] << " ";
	}
	cout << endl;
}

template <class T, int n>
void TWO::SortArray()
{
	sort(a, a + 10);
	for (int i = 0; i < n; i++)
	{
		cout << a[i] << " ";
	}
	cout << endl;
}
template <class T, int n>
TWO::~TWO()
{

}

[shadowCODE]

Sorry , i missed out some detail in the last exmaple.
Add the template argument list to to definition.

template<class T> 
void MyClass<T>:: fx1() {}

template<classT>
void MyClass<T>::fx2(){}

In your case

template <class T, int n>
void TWO<T,n>::ReadData()
{
	for (int i = 0; i < n; i++)
		{
			cin >> a[i];
		}
	
}

[alex067]

Once again, thank you very much Shadow.

I have to revise the section on template functions, cheers!