主要4默认功能重写：

代码：

#include <iostream>

using namespace std;

class Cstring{

private :

	char * data;

public :

	Cstring(const char * str =NULL);

	Cstring(const Cstring &another);

	~Cstring();	

	Cstring & operator=(const Cstring &another);

};

//赋值构造函数

Cstring & Cstring::operator=(const Cstring &another){

	if(this  == &another)

		return *this;

	delete [] data;

	data = NULL;

	data = new char(strlen(another.data) + 1 );

	strcpy(data,another.data);

    	return * this;

}

//普通构造函数

Cstring::Cstring(const char *str){

	if(str == NULL){

		data = new char[1];

		data[0] = '\0';

	}else{

		data = new char[strlen(str)+1];

		strcpy(data,str);

	}

}

//拷贝构造函数

Cstring::Cstring(const Cstring & another){

	data = new char(strlen(another.data) + 1);

	strcpy(data,another.data);

}

//析构函数

Cstring ::~Cstring(){

	delete data;

}

void main(){

	Cstring str("hello,world");

	Cstring st(str),test2;

	Cstring test1 = test2 = st;

}