Template issues

[Placidjw]

Hi all,

I was wondering if someone could help me with one of the exercises I have for uni,

The program itself works fine, however when I attempted to add a template to the class I keep getting the errors: "Cannot use template 'Bivec<T>' without specifying specialization perameters (Borland Compiler E2102) and "Declaration Terminated Incorrectly" referring to the Bivec class' constructor:

Bivec::Bivec (int lo, int hi, T initial_value): v(hi - lo + 1), low(lo)

Any suggestions most welcome,

Thanks,

Full program code:

#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>

using namespace std;

class Out_of_bounds
{
  public:
	Out_of_bounds(int elem) : bval(elem) {}
	int badval() const {return bval;}
  private:
  int bval;
};


class Pop_on_empty
{};


template <typename T>
class Bivec
{ public:
	Bivec() {low = 0;}
	Bivec (int lo, int hi, T initial_value);
	void push_back(T);
	void push_front(T);
	T pop_back() throw (Pop_on_empty);
	T pop_front() throw (Pop_on_empty);
	int& operator[](int) throw (Out_of_bounds);
	void display() const;
	bool empty() const {return v.size() == 0; }

	Bivec(const Bivec& bx) { copy(bx); }
	~Bivec() { free(); }
	const Bivec& operator=(const Bivec&);
  private:
	vector<T*> v;
	int low;
	void copy(const Bivec&);
	void free();
};

Bivec::Bivec (int lo, int hi, T initial_value): v(hi - lo + 1), low(lo)
{
	for (int i = 0; i < static_cast<int>(v.size()); i++)
		v[i] = new T(initial_value);
}
template <typename T>

template <typename T>
void Bivec<T>::push_back(T x)
{
	v.push_back(new T(x));
}

template <typename T>
void Bivec<T>::push_front(T x)
{
	v.push_back(new T(NULL));
	/*for (int i = 1; i < static_cast<int>(v.size()); i++)
		v[i] = v[i - 1];*/
		for (int i = v.size() - 1; i > 0; i--)
		v[i] = v[i-1];
	v[0] = new T(x);
	low--;
}

template <typename T>
T Bivec<T>::pop_back() throw (Pop_on_empty)
{
	if (v.empty())
		throw Pop_on_empty();
	else
	{
		T g = *v[v.size() - 1];
		v.pop_back();
		return g;
	}
}

template <typename T>
T Bivec<T>::pop_front() throw (Pop_on_empty)
{
	if (v.empty())
		throw Pop_on_empty();
	else
	{
		T g = *v[0];
		for (int i = 1; i < static_cast<int>(v.size()); i++)
			v[i - 1] = v[i];
		v.pop_back();
		low++;
		return g;
	}
}

template <typename T>
int& Bivec<T>::operator[](int n) throw (Out_of_bounds)
{
	if (n < low || n >= low + static_cast<int>(v.size()))
		throw Out_of_bounds(n);
	return *v[n - low];
}

template <typename T>
void Bivec<T>::display() const
{
	for (int i = 0; i < static_cast<int>(v.size()); i++)
		cout << *v[i] << " ";
	cout << endl;
}

template <typename T>
const Bivec<T>& Bivec<T>::operator=(const Bivec& old)
{
	if (this != &old)
	{
		free();
		copy(old);
	}
	return *this;
}

template <typename T>
void Bivec<T>::copy(const Bivec& old)
{
	v = old.v;
	low = old.low;
	for (int i = 0; i < static_cast<int>(v.size()); i++)
		v[i] = new int(*old.v[i]);
}

template <typename T>
void Bivec<T>::free()
{
	while (v.size() > 0)
	{
		v.pop_back();
	}
}


int main()
{try{	Bivec<int> b1;
	cout << "b1, initially empty: ";
	b1.display();
	for (int i = 0; i < 10; i++)
		b1.push_back(i);
	cout << "b1, after push_backs: ";
	b1.display();
	b1.push_front(66);
	b1.push_front(77);
	cout << "b1, after push_fronts: ";
	b1.display();
	int last = b1.pop_back(), first = b1.pop_front();
	cout << "last was " << last << ", first was " <<  first << endl;
	cout << "b1, after pops: ";
	b1.display();
	cout << "b1[-1] " << b1[-1] << ", b1[0] " << b1[0] << ", b1[8] " << b1[8] << endl;
	b1[-1] = 88;
	cout << "b1, after b1[-1] = 88: ";
	b1.display();

	Bivec<int> b2(-5, +5, 0);
	cout << "b2, as constructed: ";
	b2.display();

	Bivec<int> b3(b1);
	cout << "b3, copy-constructed from b1: ";
	b3.display();
	b3 = b2;
	cout << "b3, after b3 = b2: ";
	b3.display();
	cout << "Program should now terminate with exception" << endl;
//	cout << b1[50];	// should throw exception
	while( true )
		b3.pop_back();	// should throw exception

}
catch(const Out_of_bounds& ob)
{	cerr << "Invalid subscript " << ob.badval() << endl;
	exit(1);
}
catch(Pop_on_empty)
{	cerr << "Popping empty Bivec" << endl;
	exit(1);
}
} // matches { before try, needed for Borland 

[guestgulkan]

Just look at the way you have done most of the Bivec class functions
for example this one:

template <typename T>
void Bivec<T>::free()
{
	while (v.size() > 0)
	{
		v.pop_back();
	}
}

Now look at the way you have done this Bivec constructor

Bivec::Bivec (int lo, int hi, T initial_value): v(hi - lo + 1), low(lo)
{
	for (int i = 0; i < static_cast<int>(v.size()); i++)
		v[i] = new T(initial_value);
}
template <typename T> // and what is this line doing here anyway???? 

[Placidjw]

Thanks very much, I think I got too attached to the idea of the constructor being different to member functions (all the examples I looked through had the constructor fully defined in the class definition.

Thanks for putting up with my brain freeze :)

[andywestken]

Aside:

I see exception specifiers in the code above. These are pretty much deprecated these days, and to my knowledge have been so for some while. They should be avoided!!

From A Pragmatic Look at Exception Specifications
Herb Sutter
First pub: C/C++ Users Journal, 20(7), July 2002.
http://www.gotw.ca/publications/mill22.htm

    Moral #1: Never write an exception specification.

    Moral #2: Except possibly an empty one, but if I were you I’d avoid even that.

Andy