又是编译不能通过。。。唉

#include <iostream>
#include <cstring>

 using namespace std;
class book{
     private:
         char name[20];
     public:
         const book operator +( const book &b) const;
         void showbookname();
         void setname( char *str);
         const char *getname ()const;
         book(char *str);//explicit book(char *str);
};

 const book book::operator +( const book &b) const{
     char str_temp[20];
     strcpy(str_temp, this->getname());
     strcat(str_temp, b.getname());
     return book(str_temp);

 }

 const char* book::getname ()const{
     return name;

 }
void book::setname(char *str){
     strcat(name, str);

 }

 void book::showbookname(){
     cout << name << endl;

 }

 book::book(char *str){
     strcpy(name, str);

 }

 int main(){
     book book_one("Hello");
     book book_two("yes");
     book book_three = book_one + book_two;
     book book_four = book_one + "Okay!";
     book_three.showbookname();
     book_four.showbookname();
     //cout << "Hello world!" << endl;
     return 0;

 }
现在可以了，看看吧