数据结构与算法-C++实现动态变长数组

一个简单至极的变长数组，仅仅是在原生数组中添加了自动变长功能

参考STL中vector的实现，每次下标越界，就将数组容量扩大一倍。

1. 申请新的空间，是原长度的二倍
2. 从原内存复制所有内容到新内存
3. 释放原内存

/*
	Author:  trialley
	Date:    2019-7-26
	Licence: MIT
*/

#pragma once
#include<cstring>		//memset,memcpy
#include<cstdlib>		//malloc

template<typename T>
class darray{
	private:
		T* head;		//the array head pointer
		int length;		//the length of array
	public:
		darray(int n=100){
			length=n;
			head=(T*)malloc(sizeof(T)*length);
			memset(head,0,length);
		}
		
		// "&" is a must !
		T& operator [](int i){
			if(i>length){
				exlength();
				return head[i];
			}
			return head[i];
		}
		exlength(){
			int nlength=2*length;
			T* temp=head;
			head=(T*)malloc(sizeof(T)*nlength);
			memset(head,0,nlength);
			memcpy(head,temp,length);
			length=nlength;
		}
};