help with templates

[drdodirty2002]

hi all how are you doing. I have a quick question involving templates, I unfortunatley have a horrible professor for my data structures programming class at the university I'm attending. So I thought I might get ahold of you fellas here to see if you could help me out
I just need to see a very rudementry program that uses templates for three different data types int char and strings. All of them should be used in one data member in a class declaration. I'm totally lost right at the moment. The guy teaching the class really left us out to dry on this one. so far this is what I have to work with

#include <iostream.h>
#include <string.h>
//class4.cpp
const int n=3;
#include <iostream.h>
#include <string.h>


template <class T>

class myclass
{
	private:

		T a[n];
	public:
		void readdata();
		void displaydata();
		friend void displaydata(myclass p);

};
//----------------------------------------------------------------------------
template <class T>
void displaydata(myclass<T> q)
{
	for(int i=0; i<n; ++i)
		cout<<q.a[i]<<endl;
}
//-----------------------------------------------------------------------------

template <class T>
void myclass<T> ::readdata()
{
	for(int i=0; i<n; ++i)
	{
		cout<<"Enter data:"; 
		 cin>>a[i];
	}
}
//-----------------------------------------------------------------------------

template <class T>
void myclass<T> :: displaydata()
{
	for(int i=0; i<n; ++i)
		cout<<a[i]<<endl;
}
//-----------------------------------------------------------------------------

void main()
{
	myclass<float> p;
	p.readdata();
	p.displaydata();
	displaydata(p);
}

If anybody could at least point me in the right direction it would be much appreciated

[JaWiB]

A few things:

Update your headers if you can

//if you have a new enough compiler (standards compliant)
#include <iostream> //the standard headers do not have 
#include <string>     // the .h extension

using namespace std;

I'm not sure why you need a friend function here...

const int n=3;


template <class T>

class myclass
{
	private:

		T a[n];
	public:
		void readdata();
		void displaydata();
	                 //friend void displaydata(myclass p);

};

Then for your input functions you might want to do something like this:

//----------------------------------------------------------------------------
template <class T>
void displaydata(myclass<T> q)
{
	for(int i=0; i<n; ++i)
		cout<<q.a[i]<<endl;
}
//-----------------------------------------------------------------------------

//template <class T>
void myclass<float> ::readdata()
{
	for(int i=0; i<n; ++i)
	{
		cout<<"Enter data (float):"; 
		 cin>>a[i];
	}
}
void myclass<int> ::readdata()
{
	for(int i=0; i<n; ++i)
	{
		cout<<"Enter data (int):"; 
		 cin>>a[i];
	}
}

//-----------------------------------------------------------------------------

template <class T>
void myclass<T> :: displaydata()
{
	for(int i=0; i<n; ++i)
		cout<<a[i]<<endl;
}
//-----------------------------------------------------------------------------

int main()
{
	myclass<int> p;
	p.readdata();
	p.displaydata();
	
}

But its late and I'm tired so I might not understand your problem correctly

[Zach L.]

Looks pretty good. Your friend function needs to be declared a templated function (myclass is an incomplete type in itself). If you specialize your functions as JaWiB was showing, you need syntax like:

template<>
void foo<int>::bar( ) { }

And, when changing your headers, be careful about the distinction between <string> and <cstring>. The old <string.h> is now <cstring>, and contains functions such as strcpy, strcmp, etc. <string> has the std::string class.

Cheers.

[Zach L.]

As a side note, it helps if you post your specific problem. E.g. Abnormal run-time behavior (and what it is), or specific compiler errors.

[Sang-drax]

Change your friend-declaration into this:

template <typename T>
friend void displaydata(myclass<T> p);

and it'll work.