4elist1903.cpp

《21天学通C＋＋》附盘的原代码。书上的每个例子在这里都有相应的C语言程序。

// Listing 19.3 - Type specific friend functions in templates

#include <iostream>
using namespace std;

const int DefaultSize = 10;

// declare a simple Animal class so that we can
// create an array of animals

class Animal
{
public:
	Animal(int);
	Animal();
	~Animal() {}
	int GetWeight() const { return itsWeight; }
	void Display() const { cout << itsWeight; }
private:
	int itsWeight;
};

Animal::Animal(int weight):
	itsWeight(weight)
{}

Animal::Animal():
	itsWeight(0)
{}

template <class T>  // declare the template and the parameter
class Array            // the class being parameterized
{
public:
	// constructors
	Array(int itsSize = DefaultSize);
	Array(const Array &rhs);
	~Array() { delete [] pType; }

	// operators
	Array& operator=(const Array&);
	T& operator[](int offSet) { return pType[offSet]; }
	const T& operator[](int offSet) const
	{ return pType[offSet]; }
	// accessors
	int GetSize() const { return itsSize; }

	// friend function
	friend void Intrude(Array<int>);

private:
	T *pType;
	int  itsSize;
};

// friend function. Not a template, can only be used
// with int arrays! Intrudes into private data.
void Intrude(Array<int> theArray)
{
	cout << "\n*** Intrude ***\n";
	for (int i = 0; i < theArray.itsSize; i++)
		cout << "i: " <<    theArray.pType[i] << endl;
	cout << "\n";
}

// implementations follow...

// implement the Constructor
template <class T>
Array<T>::Array(int size):
	itsSize(size)
{
	pType = new T[size];
	for (int i = 0; i<size; i++)
		pType[i] = 0;
}

// copy constructor
template <class T>
Array<T>::Array(const Array &rhs)
{
	itsSize = rhs.GetSize();
	pType = new T[itsSize];
	for (int i = 0; i<itsSize; i++)
		pType[i] = rhs[i];
}

// operator=
template <class T>
Array<T>& Array<T>::operator=(const Array &rhs)
{
	if (this == &rhs)
		return *this;
	delete [] pType;
	itsSize = rhs.GetSize();
	pType = new T[itsSize];
	for (int i = 0; i<itsSize; i++)
		pType[i] = rhs[i];
	return *this;
}

// driver program
int main()
{
	Array<int> theArray;      // an array of integers
	Array<Animal> theZoo;     // an array of Animals
	Animal *pAnimal;

	// fill the arrays
	for (int i = 0; i < theArray.GetSize(); i++)
	{
		theArray[i] = i*2;
		pAnimal = new Animal(i*3);
		theZoo[i] = *pAnimal;
	}

	int j;
	for (j = 0; j < theArray.GetSize(); j++)
	{
		cout << "theZoo[" << j << "]:\t";
		theZoo[j].Display();
		cout << endl;
	}
	cout << "Now use the friend function to ";
	cout << "find the members of Array<int>";
	Intrude(theArray);

	cout << "\n\nDone.\n";
	return 0;
}