手写vector

看过JDK源码，现在自己想实现一个vector。

最开始的时候，我大概构想了一下怎么设计，一种是设置一个指针数组来存放对象，这样修改的时候可以不用大量的元素复制，但后来仔细想了想，它需要设置一个额外的位示图显示对应位置的元素情况，不划算，所以最终也是采取了JDK源码的设计思路。即，数组初始长度设置为10,以后快溢出之前将数组扩容为原先的1.5倍。

#include <iostream>
#include <cstring>
using namespace std;

class Vector {
	private :
			 int *myVector;
			 int vectorSize;
			 int length; // if vectorSize >= length need extendCapacity

	public:
			 Vector() {
			 	length = 10;
			 	myVector = new int[length];
			 	vectorSize = 0;
			 }
			 Vector(int nowSize, int value) {
			 	vectorSize = nowSize;
			 	length = nowSize > length ? nowSize : length;
			 	myVector = new int[nowSize];
			 	memset(myVector, value, nowSize);
			 }
			 ~Vector() {
			 	delete myVector;
			 	myVector = NULL;
			 }
			 int rangeCheck(int index);
			 void push_back(int value);
			 int size();
			 int erase(int index);
			 bool empty();
			 int insert(int index, int value);
			 void show();
			 void ensureCapacity();
			 void CopyFrontToEnd(int *Dst, int from, int *Src, int start, int cnt);//从前往后复制
			 void CopyEndToFront(int *Dst, int from, int *Src, int start, int cnt); //从后往前复制
};

void errPrint(int errorType) {
	if (errorType == 1) {
		cout << "index > size\n";
	}
	else if(errorType == -1) {
		cout << "index < 0\n";
	}
}

void Vector::CopyFrontToEnd(int *Dst, int from, int *Src, int start, int cnt) {
	for(int i = start; i < start + cnt; ++i) {
		Dst[from++] = Src[i];
	}
}

void Vector::CopyEndToFront(int *Dst, int from, int *Src, int start, int cnt) {
	for(int i = start - 1; i >= start - cnt; --i) {
		Dst[from--] = Src[i];
	}
}

void Vector::ensureCapacity() {
	if(vectorSize >= length) {
		int *tmp = new int[length * 3 / 2];
		length *= 3 / 2;
		CopyFrontToEnd(tmp, 0, myVector, 0, vectorSize);
		myVector = tmp;
	}
}

int Vector::rangeCheck(int index) {
	if (index > vectorSize) {
		return 1;
	}
	if (index < 0) {
		return -1;
	}
	return 0;
}

void Vector::push_back(int value) {
	ensureCapacity();
	myVector[vectorSize++] = value;
}

int Vector::size() {
	return vectorSize;
}

int Vector::erase(int index) {
	int checkOut = rangeCheck(index);
	if(checkOut != 0)
		return checkOut;
	CopyFrontToEnd(myVector, index, myVector, index + 1, vectorSize - index - 1);
	--vectorSize;
}

bool Vector::empty() {
	return vectorSize == 0 || myVector == NULL;
}

int Vector::insert(int index, int value) {
	int checkOut = rangeCheck(index);
	if(checkOut != 0)
		return checkOut;
	ensureCapacity();
	CopyEndToFront(myVector, vectorSize, myVector, vectorSize, vectorSize - index);
	myVector[index] = value;
	++vectorSize;
	return 0;
}

void Vector::show() {
	for (int i = 0; i < vectorSize; ++i) {
		cout << myVector[i] << " ";
	}
	cout << endl;
}

void menu() {
	cout << "1-push_back  2-size  3-erase  4-empty 5-insert 6-show\n";
}

void testVector(Vector myVector) {
	int choice, index, value, checkOut;
	menu();
	while(cin >> choice) {
		switch(choice) {
			case 1:
				cout << "cin the value you want to push_back : ";
				cin >> value;
				myVector.push_back(value);
				break;
			case 2:
				cout << "vector size = " << myVector.size() << endl;
				break;
			case 3:
				cout << "cin the index : ";
				cin >> index;
				checkOut = myVector.rangeCheck(index);
				if(checkOut == 0)
					myVector.erase(index);
				else
					errPrint(checkOut);
				break;
			case 4:
				cout << "vector empty : " << myVector.empty() << endl;
				break;
			case 5:
				cout << "cin the index and the value you want to insert: ";
				cin >> index >> value;
				checkOut = myVector.rangeCheck(index);
				if(checkOut == 0)
					myVector.insert(index, value);
				else
					errPrint(checkOut);
				break;
			case 6:
				cout << "show vector : ";
				myVector.show();
				break;
			default :
				break;
		}
	}
}

int main(int argc, char const *argv[]) {
	Vector myVector;
	testVector(myVector);
	return 0;
}