可变长数组类的实现

using namespace std;

class CArray {
     
	int size;
	int* ptr;
public:
	CArray(int s = 0);
	CArray(CArray& a);
	~CArray();
	void push_back(int v);
	CArray& operator=(const CArray& a);
	int length() {
      return size; }
	int & operator[](int i)
	{
     
		return ptr[i];
	}
};

CArray::CArray(int s) :size(s)
{
     
	if (s == 0)
		ptr = NULL;
	else
		ptr = new int[s];
}

CArray::CArray(CArray& a) {
     
	if (!a.ptr) {
     
		ptr = NULL;
		size = 0;
		return;
	}
	ptr = new int[a.size];
	memcpy(ptr, a.ptr, sizeof(int) * a.size);
	size = a.size;
}

CArray::~CArray()
{
     
	if (ptr)delete [] ptr;
}

CArray& CArray::operator=(const CArray& a)
{
     
	if (ptr == a.ptr)
		return *this;
	if (a.ptr == NULL) {
     
		if (ptr) delete[]ptr;
		ptr = NULL;
		size = 0;
		return *this;
	}
}

void CArray::push_back(int v)
{
     
	if (ptr)
	{
     
		int* tmpPtr = new int[size + 1];
		memcpy(tmpPtr, ptr, sizeof(int) * size);
		delete[]ptr;
		ptr = tmpPtr;
	}
	else
		ptr = new int[1];
	ptr[size++] = v;
}

int main() {
     
	CArray a;
	for (int i = 0; i < 5; ++i)
	{
     
		a.push_back(i);
	}
	CArray a2, a3;
	a2 = a;
	for (int i = 0; i < a.length(); ++i)
		cout << a2[i] << " ";
	a2 = a3;
	for (int i = 0; i < a2.length(); ++i)
		cout << a2[i] << " ";
	cout << endl;
	a[3] = 100;
	CArray a4(a);
	for (int i = 0; i < a4.length(); ++i)
		cout << a4[i] << " ";
	return 0;
}