UNP_1_Chapter 3__基本socket
进程->内核，传递socket地址的函数：bind、connect、sendto
进程<-内核，传递socket地址的函数：accept、recvfrom、getsockname、getpeername

//使用前置0，好习惯bzero(x,sizeof(struct sockaddr_in));struct sockaddr_in{  uint8_t        sin_len;    //不一定有  sa_family_t    sin_family; //不一定有  in_port_t      sin_port;  struct in_addr sin_addr;  unsigned char  sin_zero[8];};typedef uint32_t in_addr_t;struct in_addr{  in_addr_t s_addr;};//struct sockaddr{  uint8_t  sa_len;  sa_family_t   sa_family;  char          sa_data[14];};