改写String类别

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] = '';
	}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;
}