<四>MyVector中加入迭代器功能

我们之前有<C++模板编程模块>中的第<四>节 理解空间配置器allocator优化STL中的Vector
我将在此基础上加入迭代器功能代码


Iterator 为什么可以遍历所有的容器的方式都一样?
auto it =continer.beign();
for( ;it!=continer.end();++it){
    cout<<*it<<endl;
}

//我们在自己的容器里的 Iterator  de ++ , * 由自己来实现,所有对外部使用者来看都是统一的.
//泛型算法能够给所有的容器都使用,也是基于容器对外提供了统一的遍历接口, 其参数接受的都是容器的迭代器


#include <iostream>
using namespace std;


class person {
public:
	//构造函数
	person(int _age=1,char * _pname=nullptr):
	age(_age)
	{
		if (_pname == nullptr) {
			pname = new char[1];
			pname[0] = '\0';
		}
		else {
			int size = strlen(_pname);
			pname = new char[size + 1];
			strcpy(pname, _pname);
		}
		cout << "创建student对象,地址=" << this << endl;
	}
	//拷贝构造函数
	person(const person & _person) {
		this->age = _person.age;
		int size = strlen(_person.pname);
		pname = new char[size + 1];
		strcpy(this->pname, _person.pname);

	}

	//赋值函数
	person & operator=(const person & _person) {
		if (this == &_person) { return *this; }
		delete[]pname;
		pname = nullptr;
		this->age = _person.age;
		int size = strlen(_person.pname);
		pname = new char[size + 1];
		strcpy(this->pname, _person.pname);
		return *this;
	}
	~person() {
		cout << "析构 person =" <<pname << " "<<age << endl;
		delete[]pname;
		pname = nullptr;		
	}

	
private:
	int age;
	char * pname;
	friend ostream & operator<<(ostream & out, const person & _value);
};

ostream & operator<<(ostream & out, const person & _value) {
	cout << _value.pname<<" == "<< _value.age << " "  << endl;
	return out;
}


template <typename T>
class Allocate4 {

public:
	
	//分配内存空间,不创建对象
	T * allocator(int size=4) {
		return (T *)malloc(sizeof(T)*size);
	}
	
	//在指定的内存空间地址,构建 T对象
	void constract(T * pAddress, const T & _val) {
		new (pAddress) T(_val);
	}

	//释放指定位置的内存空间
	void delAllocator(T * pAddress) {
		if (pAddress != nullptr) {
			free(pAddress);
			pAddress = nullptr;
		}
	}

	//析构指定内存位置
	void destory(T * pAddress) {
		pAddress->~T();//调用析构函数
	}

};


template<typename T,typename Allocate= Allocate4<T>>
//类模板
class MyVector4 {

public:

	MyVector4<T,Allocate>(int size = 4 , const Allocate _rallocator = Allocate4<T>)
	: _allocator(_rallocator)
	{
		pfirst = _allocator.allocator(size);
		last = pfirst;
		pend = pfirst + size;
		cout << "MyVector开辟内存地址=" << pfirst<<endl;
	}

	MyVector4<T, Allocate>(const MyVector4<T, Allocate> & _vector)
	{
		//1:根据原vector的空间大小申请新的内存空间
		pfirst = _allocator.allocator(_vector.size());
		last   = pfirst;
		pend   = pfirst + size;

		//2:将原vector空间中的有效对象赋值到新的vector中
		T * _pFlag = _vector.pfirst;
		while (_pFlag != _vector.last) {
			_allocator.constract(last, *_pFlag);
			_pFlag++;
			last++;
		}
	}

	MyVector4<T, Allocate> & operator=(const MyVector4<T, Allocate> & _vector)
	{
		if (this == &_vector) {
			return *this;
		}

		//1:析构现有vector中的有效对象
		T * _pFlag = pfirst;
		while (_pFlag !=last) {
			_allocator.destory(_pFlag);
			_pFlag++;
		}

		//2:释放现有的vector申请的堆内存空间
		_allocator.delAllocator(pfirst);
		pfirst = nullptr;
		pend = nullptr;
		last = nullptr;

		//3:根据_vector的内存空间大小,申请新的堆内存空间
		pfirst = _allocator.allocator(_vector.size());
		last = pfirst;
		pend = pfirst + _vector.size();
		
		//4:将_vector中有效的对象复制到现在新的堆空间中	
		T * _pFlag = _vector.pfirst;
		while (_pFlag != _vector.last) {
			_allocator.constract(last, *_pFlag);
			_pFlag++;
			last++;
		}
		
	}

	void pushBack(const T & _val)  {
		if (Full()) {
			Expend();
		}
		_allocator.constract(last, _val);	
		cout << "pushBack 原对象 地址=" << &_val  <<"放在内存位置 "<<last<< endl;
		this->last++;
	}

	void popBack()  {
		if (Empty()) { return ; }
		_allocator.destory(this->last-1);
		this->last--;
	}

	//内存空间扩展
	void Expend() {
		int newSize = 2*this->size();
		
		//1:申请新的内存空间
		T * tep_pfirst = _allocator.allocator(newSize);
		T * tep_last = tep_pfirst;
		T * tep_pend = tep_pfirst + newSize;

		//2:原当前vector中原有效的对象复制到新的堆空间上
		T * _pFlag = pfirst;
		while (_pFlag != last) {
			_allocator.constract(tep_last, *_pFlag);
			_pFlag++;
			tep_last++;
		}

		//3:析构原有对象
		_pFlag = pfirst;
		while (_pFlag != last) {
			_allocator.destory(_pFlag);
			_pFlag++;
		}

		//4:释放原有的vector申请的堆内存空间
		_allocator.delAllocator(pfirst);
		pfirst = nullptr;
		pend = nullptr;
		last = nullptr;

		//5:指针重新指向
		pfirst = tep_pfirst;
		last   = tep_last;
		pend   = tep_pend;

		cout << "MyVector空间2倍扩展,新的地址=" << pfirst << endl;
	}

	bool Empty() const {
		return this->pfirst == this->last;
	}
	
	bool Full() const {
		return this->pend == this->last;
	}
	int size() {
		return this->pend - this->pfirst;
	}

	void showVectorInfo() {
		T * tep = pfirst;
		while (tep < last)
		{
			cout << "打印Vector中有效对象地址=" << tep << endl;
			tep++;
		}
	}

	//定义属于自己的迭代器
	class Iterator {

	public:

		Iterator( T * _pAddress=nullptr):pAddress(_pAddress) {
		}

		const T & operator*() const {
			return *pAddress;
		}

		T & operator*() {
			return *pAddress;
		}
		//前置++
		void operator++() {
			this->pAddress++;
		}

		bool operator!=(const Iterator & src) const {
			return this->pAddress != src.pAddress;
		}

	private:
		T * pAddress;
	};

	Iterator begin() const {
		return Iterator(this->pfirst);
	}

	Iterator end() const {
		return Iterator(this->last);
	}

private:
	T * pfirst;//指向首元素地址
	T * pend;  // 指向容器最后位置的下一个地址
	T * last;  //指向最后一个有效元素的下一个位置
	Allocate _allocator;
};



void testV4() {

	MyVector4<person, Allocate4<person>> v5(4,Allocate4<person>());

	person p1(10,"zs1");
	v5.pushBack(p1);

	person p2(20, "zs2");
	v5.pushBack(p2);

	person p3(30, "zs3");
	v5.pushBack(p3);

	person p4(40, "zs4");
	v5.pushBack(p4);

	v5.showVectorInfo();

	cout << "-------" << endl;
	person p5(50, "zs5");
	v5.pushBack(p5);

	v5.showVectorInfo();


	v5.popBack();

	MyVector4<person, Allocate4<person>>::Iterator  it_begin = v5.begin();
	MyVector4<person, Allocate4<person>>::Iterator  it_end   = v5.end();

	cout << "---iterator begin----" << endl;
	
	for (; it_begin != it_end; ++it_begin) {
		cout << *it_begin << endl;
	}

	cout << "---iterator end----" << endl;

}


int main() {

	testV4();
	system("pause");
	return 0;

}//pendl

作者:Hello_Bugs 原文地址:https://www.cnblogs.com/erichome/p/16915769.html

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