学步园

我们设计动态数组的目的在于，利用C++模板技术，消除C++语言中对数组的种种限制，如数组无法成为函数的参数或返回值（除非是指针），数组无法直接赋值等等。

1 一维动态数组

一维动态数组将一个普通数组封装成data：

来看具体实现：

template <class T>
class Array
{
protected:
	T* data;
	unsigned int base;
	unsigned int length;

public:
	Array ();
	Array (unsigned int, unsigned int = 0);
	~Array ();

	Array (Array const&);
	Array& operator = (Array const&);

	T const& operator [] (unsigned int) const;
	T& operator [] (unsigned int);

	T const* Data () const;
	unsigned int Base () const;
	unsigned int Length () const;

	void SetBase (unsigned int);
	void SetLength (unsigned int);
};

template <class T>
Array<T>::Array() :
data (new T [0]),
base (0),
length (0)
{}

template <class T>
Array<T>::Array (unsigned int n, unsigned int m) :
data (new T [n]),
base (m),
length (n)
{}

template <class T>
Array<T>::Array (Array<T> const& array) :
data (new T [array.length]),
base (array.base),
length (array.length)
{
	for (unsigned int i = 0; i < length; ++i)
	{
		data [i] = array.data [i];
	}
}

template <class T>
Array<T>::~Array ()
{ 
	delete [] data; 
}

template <class T>
T const* Array<T>::Data() const
{ 
	return data; 
}

template <class T>
unsigned int Array<T>::Base() const
{ 
	return base; 
}

template <class T>
unsigned int Array<T>::Length() const
{ 
	return length; 
}

template <class T>
T const& Array<T>::operator [] (unsigned int position) const
{
	unsigned int const offset = position - base;
	if (offset >= length)
	{
		throw out_of_range ("invalid position");
	}

	return data [offset];
}

template <class T>
T& Array<T>::operator [] (unsigned int position)
{
	unsigned int const offset = position - base;
	if (offset >= length)
	{
		throw out_of_range ("invalid position");
	}

	return data [offset];
}

template <class T>
void Array<T>::SetBase (unsigned int newBase)
{ 
	base = newBase; 
}

template <class T>
void Array<T>::SetLength (unsigned int newLength)
{
	T* const newData = new T [newLength];
	unsigned int const min =
		length < newLength ? length : newLength;
	for (unsigned int i = 0; i < min; ++i)
	{
		newData [i] = data [i];
	}

	delete [] data;
	data = newData;
	length = newLength;
}

2 二维动态数组

二维动态数组的实现比一维数组更简单：

template <class T>
class Array2D
{
protected:
	unsigned int numberOfRows;
	unsigned int numberOfColumns;
	Array<T>* array;

public:
	Array2D (unsigned int, unsigned int);
	//T& Select (unsigned int, unsigned int);
	Array<T> const& operator[](unsigned int index) const{ //const版本
		return array[index]; //返回索引处的一维数组对象
	}
	Array<T>& operator[](unsigned int index){ //非const版本
		return array[index]; //返回索引处的一维数组对象
	}
};

template <class T>
Array2D<T>::Array2D( unsigned int m, unsigned int n ):
numberOfRows (m),
numberOfColumns (n),
array (0)
{
	//为一维数组Array<T>分配原始内存
	void* raw=::operator new[](numberOfColumns * sizeof(Array<T>));
	array=static_cast<Array<T>*>(raw);
	//用placement new调用构造函数初始化各个元素的内存
	for(std::size_t i=0;i<numberOfColumns;++i)
		new(array+i) Array<T>(numberOfRows);
}