text: #include "csapp.h"
  int main(int argc,char **argv)
  {
      struct in_addr inaddr;
      unit32_t addr;
      char buf[MAXBUF];
      if(argc!=2){
          fprintf(stderr,"usage: %s <hex number>\n",argv[0]);
      }
  
      sscanf(argv[1],"%x",&addr);
      inaddr.s_addr=htonl(addr);
  
      print("%s\n",buf);
      exit(0);
  }
  
  /*
  当前项目的作用是：把16进制的数据，转换成点十进制
  
  > gcc hex2dd.c
  > ./a.out 0x8002c2f2  
  > 128.2.194.242
  */