【C++】String类中的运算符重载

模块化设计：

头文件：

<span style="font-size:18px;">

#ifndef operator_operator_h
#define operator_operator_h

#include <iostream>  
#include <string>  

using namespace std;

class MyString
{
public:
	//三个重载的构造函数  
	MyString();
	MyString(const char* str);
	MyString(const MyString& str);
	//析构函数  
	~MyString();

	//重载运算符  
	MyString& operator = (const MyString& str);
	char&  operator[](int index);//訪问下标
	friend ostream& operator << (ostream& out, const MyString& str); //重载输出操作符  
	friend istream& operator >> (istream& in, MyString& str); //重载输入操作符  
	friend MyString operator + (const MyString& str1, const MyString& str2); //重载加号操作符。注意返回引用不行
	friend MyString operator += (MyString& str1, const MyString& str2); //重载+=操作符  
	friend bool operator == (const MyString& str1, const MyString& str2);   //重载相等操作符  
	friend bool operator != (const MyString& str1, const MyString& str2);   //重载不相等操作符  

private:
	char* p;
	int len;
};



#endif;

</span>

功能函数：

<span style="font-size:18px;">

#include "operator.h"

//默认构造函数，初始化为空串  
MyString::MyString()
{
	len = 0;
	p = new char[len + 1];
	p[0] = '\0';
}

//构造函数，用一个字符串初始化  
MyString::MyString(const char* str)
{
	len = strlen(str);
	p = new char[strlen(str) + 1];
	strcpy_s(p, strlen(str) + 1, str);
}

//拷贝构造函数，用另外一个string初始化  
MyString::MyString(const MyString& str)
{
	len = str.len;
	p = new char[strlen(str.p) + 4];
	strcpy_s(p, strlen(str.p) + 1, str.p);
}

//析构函数  
MyString::~MyString()
{
	delete[] p;
}

//重载赋值操作符( = )  
MyString& MyString::operator = (const MyString& str)
{
	if (this->p == str.p)
	{
		return *this;
	}
	delete[] p;
	len = str.len;
	p = new char[len + 1];
	strcpy_s(p, len + 1, str.p);
	return *this;
}

//重载输出操作符( << )  
ostream& operator << (ostream& out, const MyString& str)
{
	out << str.p;
	return out;
}

//重载输入操作符( >> )  
istream& operator >> (istream& in, MyString& str)
{
	in >> str.p;
	return in;

}

//重载加号操作符( + )  
MyString operator + (const MyString& str1, const MyString& str2)
{
	MyString str;
	delete[] str.p;
	str.len = str1.len + str2.len;
	str.p = new char[str.len + 1];
	strcpy_s(str.p, str.len + 1, str1.p);
	strcat_s(str.p, str.len + 1, str2.p);
	return str;
}

//重载相加赋值操作符( += )  
MyString operator += (MyString& str1, const MyString& str2)
{
	str1 = str1 + str2;
	return str1;
}

//重载相等操作符  
bool operator == (const MyString& str1, const MyString& str2)
{
	if (strcmp(str1.p, str2.p) == 0)
	{
		return true;
	}
	return false;
}

//重载不相等操作符  
bool operator != (const MyString& str1, const MyString& str2)
{
	if (strcmp(str1.p, str2.p) == 0)
	{
		return false;
	}
	return true;
}


//重载下标（[]）
char&  MyString::operator[](int index)
{
	return p[index];
}


</span>

測试程序：

<span style="font-size:18px;"> 
#include "operator.h"

int main()
{
	MyString mystr("asfasgdhf");  //測试构造函数，用一个字符串初始化  

	cout << mystr[2] << endl;

	mystr[4] = 'd';

	cout << mystr <<endl;

	MyString mystr2(mystr); //用另外一个string初始化  

	cout << mystr2 << endl;

	MyString mystr3;

	mystr3 = mystr + mystr2; //測试加号运算符，測试赋值运算符  

	cout << mystr + mystr2 << endl;

	mystr3 += mystr; //測试+=运算符  

	cout << mystr3 << endl;

	cout << (mystr == mystr2) << endl;  //測试 ==  

	cout << (mystr != mystr3) << endl;  //測试 。=  


	MyString mystr4;

	cout << "Input a series characters, end of ctrl+z." << endl;

	cin >> mystr4;    //測试重载的输入符号( >> )  

	cout << mystr4 << endl;

	return 0;
}
</span>

执行结果：