<三>自己實現string,加入迭代器功能

迭代器的功能:
提供一種統一的方式,來透明的遍歷容器
理解 begin()方法,end()方法, ++ , * 的用處
其中 C++11 中提供的foreach的方式,其底層還是通過迭代器來進行遍歷的.

#include <iostream>
using namespace std;

class MyString2 {

public:

	//構造函數
	MyString2(const char * pSource = nullptr) {
		if (pSource != nullptr) {
			pString = new char[strlen(pSource) + 1];
			strcpy(pString, pSource);
		}
		else {
			pString = new char[1];
			pString[0] = '\0';
		}
		cout << "MyString構造函數,對象地址=" << this << endl;
	}

	//拷貝構造
	MyString2(const MyString2 & _rValue) {

		pString = new char[strlen(_rValue.pString) + 1];
		strcpy(pString, _rValue.pString);
		cout << "MyString拷貝構造函數" << endl;
	}

	//賦值函數
	MyString2 & operator=(const MyString2 & _rValue) {

		if (this == &_rValue) {
			return *this;
		}
		delete[] this->pString;
		this->pString = nullptr;

		char * _tpString = new char[strlen(_rValue.pString) + 1];
		strcpy(_tpString, _rValue.pString);

		cout << "MyString賦值函數" << endl;

	}

	//可編輯
	char & operator[](int index) {

		int len = strlen(this->pString);
		if (index<0) { return pString[0]; }
		else if (index>len) { return pString[index]; }
		else { return pString[index]; }

	}

	//不可編輯
	const char operator[](int index) const {

		int len = strlen(this->pString);
		if (index<0) { return pString[0]; }
		else if (index>len) { return pString[index]; }
		else { return pString[index]; }

	}

	bool operator>(const MyString2 & _rValue) const {
		return strcmp(this->pString, _rValue.pString)>0;
	}
	
	bool operator<(const MyString2 & _rValue) const {
		return strcmp(this->pString, _rValue.pString)<0;
	}
	
	bool operator==(const MyString2 & _rValue) const {
		return strcmp(this->pString, _rValue.pString) == 0;
	}

	int length() const {
		return strlen(this->pString);
	}

	~MyString2() {
		if (this->pString != nullptr) {
			delete[] this->pString;
			this->pString = nullptr;
			cout << "MyString析構函數" << this << endl;
		}
	}

	const char * c_str()  const { return this->pString; }

	//給Mystring 設計迭代器
	class Iterator {
		public:

			Iterator(char * _p=nullptr):p(_p) {
				this->p = _p;
			}
		    char & operator*() {
				return *p;
			}

			//前置++
			void operator++() {
				p++;
			}
			//
			bool operator!=(const Iterator & _val) {		
				return p!=_val.p;
			}
		private:

			char * p;
	};
	// begin() 返回的 用MyString的首元素地址，通過Iterator封裝一下
	Iterator begin() const {
		return  Iterator(this->pString);
	}
	// end() 返回的是 用 MyString 的最尾元素的下一個地址 再用Iterator封裝一下
    Iterator end() const {
		return  Iterator(this->pString+this->length());
	}

private:
	char * pString;
	friend MyString2 operator+  (const MyString2 & s1, const MyString2 &s2);
	friend ostream & operator<<(ostream & out, const MyString2 &s);
	
};

MyString2 operator+(const MyString2 & s1, const MyString2 &s2) {

	/*
	方式1 這段代碼有 記憶體泄漏問題  tp 沒有釋放掉
	int newLength = strlen(s1.pString) + strlen(s2.pString) + 1;
	char *tp = new char[newLength + 1];//重新申請空間
	strcpy(tp, s1.pString);
	strcat(tp, s2.pString);

	MyString s(tp);
	cout << "operator+ = " << &s << endl;
	return s;
	*/

	/*
	方式2 對比方式1 效果更高
	*/
	MyString2 s;
	int newLength = strlen(s1.pString) + strlen(s2.pString) + 1;
	s.pString = new char[newLength + 1];//重新申請空間
	strcpy(s.pString, s1.pString);
	strcat(s.pString, s2.pString);
	cout << "operator+ = " << &s << endl;
	return s;
}

ostream & operator<<(ostream & out, const MyString2 &s) {
	cout << s.pString << endl;
	return out;
}

void test2() {

	MyString2 s1("12345");
	MyString2 s2("6789ABC");

	cout << s1 << endl;
	cout << s2 << endl;

	MyString2 s3 = s1 + s2;
	cout << s3 << endl;
	cout << "s3 = " << &s3 << endl;

	for (int i = 0; i < s3.length(); i++) {
		cout << s3[i] << endl;
	}

	cout << "--------------------" << endl;
	s3[0] = 'W';
	for (int i = 0; i < s3.length(); i++) {
		cout << s3[i] << endl;
	}

	const MyString2 s4("hello");

	for (int i = 0; i < s4.length(); i++) {
		cout << s4[i] << endl;
	}

	cout << "------iterator Begin------" << endl;
	MyString2::Iterator it_begin = s4.begin();
	MyString2::Iterator it_end   = s4.end();

	for (  ;it_begin!=it_end; ++it_begin) {
	
		cout << *it_begin <<" ";

	}
	cout << endl;
	cout << "------iterator End------" << endl;


}
int main() {
	test2();
	system("pause");
	return 0;
}