<二>自己實作簡單的string

我們結合運算子多載知識實作string 類
在自己實作的String類中可以參考C++中string的方法
例如構造，加法，大小比較,長度，[] 等操作.
當前的MyString 類中,暫時不加入迭代器,我們將在下一節中加入迭代器的代碼.

#include <iostream>
using namespace std;

class MyString {

public:

	//建構式
	MyString(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建構式,物件地址="<<this << endl;
	}

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

		pString = new char[strlen(_rValue.pString) + 1];
		strcpy(pString, _rValue.pString);
		cout << "MyString拷貝建構式" << endl;
	}

	//賦值函式
	MyString & operator=(const MyString & _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賦值函式" << 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 MyString & _rValue) const {
		return strcmp(this->pString, _rValue.pString)>0;
	}
	bool operator<(const MyString & _rValue) const {
		return strcmp(this->pString, _rValue.pString)<0;
	}
	bool operator==(const MyString & _rValue) const {
		return strcmp(this->pString, _rValue.pString)==0;
	}

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

	~MyString() {
		if (this->pString != nullptr) {
			delete[] this->pString;
			this->pString = nullptr;
			cout << "MyString解構式" << this << endl;
		}
	}

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

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

};

MyString operator+(const MyString & s1, const MyString &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
	*/
	MyString 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 MyString &s) {
	    cout << s.pString << endl;
		return out;
}

void test() {

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

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

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

}
int main() {

	test();

	system("pause");
	return 0;
}

標籤：其他

上一篇：Java——例外處理(概念理解)

下一篇：SpringBoot之用攔截器避免重復請求