##是连接符号，连接两个宏

eg:
#include <iostream>

#define s5(a) supper_##a

void supper_printf(const char* p )
{
printf("this is supper printf:\n%s\n",p);
}

int main()
{
s5(printf)("hello owrld");

std::cout<<"Over"<<std::endl;
getchar();
return 0;
}