C++学习日记——运算符重载

C++运算符重载:赋予运算符另一种作用，实现自定义类型的运算
如对象+对象变成int+int一样
C++运算符重载内容：
1.友元重载 /友元=》声明 友元关系是单向的，不可传递/
2.输入输出流重载

class CString
{
public:
	CString(char *p = NULL){
		if(p!= NULL)
		{
			_pstr=new char[strlen(p)+1];
			strcpy(_pstr,p);
		}
		else
		{
			_pstr=new char[1];
			*_pstr=0;
		}
	}
	~CString()
	{
		delete []_pstr;
		_pstr=NULL;
	}
	CString(const CString &src)
	{
		_pstr=new char[strlen(src._pstr)+1];
		strcpy(_pstr,src._pstr);
	}
	CString& operator=(const CString &src)
	{
		if(*this == src)
		{return *this;}
		delete []_pstr;
		_pstr=new char[strlen(src._pstr)+1];
		strcpy(_pstr,src._pstr);
		return *this;
	}
	bool operator>(const CString &src)const//对象之间>的重载
	{
		return strcmp(this->_pstr,src._pstr)>0;
	}
	bool operator<(const CString &src)const//对象之间<的重载
	{
		return strcmp(this->_pstr,src._pstr)<0;
	}
	bool operator==(const CString &src)const//对象之间=的重载
	{
		return strcmp(this->_pstr,src._pstr)==0;
	}
	int length()const
	{
		return strlen(this->_pstr)+1;
	}
	char operator[](int index)const//对象之间[]的重载
	{
		return this->_pstr[index];
	}
	const char* c_str()const
	{
		return this->_pstr;
	}
private:
	char *_pstr;
	friend CString operator+(const CString &lhs, const CString &rhs);//友元声明
    friend ostream& operator<<(ostream &out, const CString &str);//友元声明
};
CString operator+(const CString &lhs, const CString &rhs)//对于对象+对象的重载
{//这里并不能返回引用，原因：返回引用时，定义的临时对象并不能被析构，程序运行不
 //下去;不加引用时，返回的对象会被保存一个临时对象返回回去；
	char*tem=new char[strlen(lhs._pstr)+strlen(rhs._pstr)+2];
	strcpy(tem,lhs._pstr);
	strcat(tem,rhs._pstr);
	CString tmp(tem);
	delete []tem;
	return tmp;
}
ostream& operator<<(ostream &out, const CString &str)//输出重载，cout的返回值类型是ostream
{
	out<<str._pstr;
	return out;
}
int main()
{
	CString str1 = "aaa";
	CString str2 = str1;
	CString str3;
	str3 = str1;
	cout<<str1<<endl;
	CString str4 = str1 + str3;
	str4 = str1 + "bbb";
	str4 = "ccc" + str1;
	cout << str4 << endl;

	if (str4 > str1)
	{
		cout << "str4 > str1" << endl;
	}
	else
	{
		cout << "str4 < str1" << endl;
	}

	int len = str4.length();
	for (int i = 0; i < len; i++)
	{
		cout << str4[i]<<" ";
	}
	cout << endl;
	char buf[1024] = { 0 };
	strcpy(buf, str4.c_str());
	cout << "buf:" << buf << endl;

	return 0;
}