类的运算符重载(string)

Mystring.h

#ifndef _MYSTRING_H
#define _MYSTRING_H
#include<string.h>
#include<iostream>
using namespace std;
class Mystring 
{
	friend ostream &operator <<(ostream &out,const Mystring &s);
	friend istream &operator >>(istream &in,Mystring &s);
	private:
	char *m_data;
	int m_lenth;
	public:
	Mystring();
	Mystring(char *str);
	Mystring(int l,char ch);
	Mystring(const Mystring &s);
	Mystring &operator =(const Mystring &s);
	Mystring &operator =(const char *str);
	Mystring &operator +=(const Mystring &s);
	char &operator [](int index);
};

#endif

Mystring.cpp

#include"Mystring.h"
#include<string.h>
using namespace std;

Mystring::Mystring()   
{
	m_data=new char;          //要给m_data分配一定内存空间  new char
	m_lenth=1;
}
Mystring::Mystring(char *str)
{
	m_lenth=strlen(str);
	m_data=new char[m_lenth];
	strcpy(m_data,str);
	
}
Mystring::Mystring(int l,char ch)
{
	m_lenth=l;
	m_data=new char[m_lenth+1];
	for(int i=0;i<l;i++)
		*(m_data+i)=ch;
	m_data[l]='\0';          //在用单个字符给数组赋值，末尾需加上'\0'结尾
}
Mystring::Mystring(const Mystring &s)
{
	m_lenth=s.m_lenth;
	m_data=new char[m_lenth+1];
	strcpy(m_data,s.m_data);
}
ostream &operator <<(ostream &out,const Mystring &s)
{
	out<<s.m_data;
	return out;
}
istream &operator >>(istream &in,Mystring &s)
{
	char *tmp=new char[1024];            //需要一个tmp来接受in的数据 再向对象赋值
	in>>tmp;
	delete s.m_data;
	s.m_data=tmp;
	s.m_lenth=strlen(tmp)+1;
	
	return in;
}
Mystring &Mystring::operator =(const Mystring &s)
{
	if(m_data!=NULL)
	{
		delete m_data;
	}
	m_lenth=strlen(s.m_data);
	m_data=new char[m_lenth+1];
	strcpy(m_data,s.m_data);
	
}
Mystring &Mystring::operator =(const char *str)
{
	if(m_data!=NULL)
	{
		delete m_data;
	}
	m_lenth=strlen(str);
	m_data=new char[m_lenth];
	strcpy(m_data,str);
} 
Mystring &Mystring::operator +=(const Mystring &s)
{
	m_lenth=m_lenth+s.m_lenth;           //  先将m_data数据取出
	char *tmp=new char[m_lenth+1];
	strcpy(tmp,m_data);
	strcat(tmp,s.m_data);               //对tmp操作
	delete m_data;
	m_data=new char[m_lenth+1];
	strcpy(m_data,tmp);
	//return *this;
}
char &Mystring::operator [](int index)
{
	return m_data[index];
}

main.cpp

#include<iostream>
#include"Mystring.h"
using namespace std;
int main()
{
	Mystring s1;
	Mystring s2("Hello");
	Mystring s3(10,'c');
	Mystring s4(s2);
	Mystring s5;
	
	cout<<s1<<endl;
	cout<<s2<<endl;
	cout<<s3<<endl;
	cout<<s4<<endl;
	
	/* cin>>s1;
	cout<<s1<<endl; */
	s1=s2;
	cout<<s1<<endl;
	s5="hi";
	cout<<s5<<endl;
	s5+=s2;
	cout<<s5<<endl;
}