c++连接字符串（重载运算符+=）

#include<iostream>
#include<string.h>
using namespace std;
class KB
{
	private:
		char *s;//字符串
	public:
	 KB(const char *p=0)
	 {
	 	s=new char[strlen(p)+1];
	 	strcpy(s,p);
	  } 
	  friend KB &operator+=(KB &str1,KB &str2)
	  {
	  	char *k=new char[strlen(str1.s)+strlen(str2.s)+1];
	  	strcpy(k,str1.s);
	  	strcat(k,str2.s);
	  	str1.s=new char[strlen(k)+1];
	  	strcpy(str1.s,k);
	  	return str1;
	  }
	  void print()
	  {
	  	cout<<s<<endl;
	  }
};
int main()
{
	KB z1("abcd"),z2("1234");
	z1+=z2;
	z1.print();
}