Several configuration functions of socket

int setsockopt(int sockfd, int level, int optname, const void *optval, socklen_t optlen); sockfd : a descriptor that identifies a socket level : level of option definitionSOL_SOCKET,IPPROTO_TCP,IPPROTO_IPandIPPROTO_IPV6 optname : the option to set optval : pointer to the buffer where the option value is stored optlen : optvalbuffer length Returns 0 on success, -1 on failure 1.  If the socket that is already in the  ESTABLISHED state ( usually distinguished by the port number and identifier) ​​calls closesocket (generally will not be closed immediately but go through the process of TIME_WAIT ) and want to continue to reuse the socket : ( Do not write close description in the program In fact, it doesn’t matter if you write or not, here it is set to be reused )   The previous programming did not set this, and it cannot be reused by default, so only one server can run, not multiple at the same time; this interface can achieve load balancing at the system level. int reuse=1;   the default value is 0 setsockopt(s,SOL_SOCKET ,SO_REUSEADDR,(const char*)&reuse,sizeof(int));

int getsockname(int sockfd, struct sockaddr *addr, socklen_t *addrlen);         \\ Get the local socket information and return 0 if it succeeds, and -1 if it fails.

int getpeername(int sockfd, struct sockaddr *addr, socklen_t *addrlen);         \\ Get the address of the accepted client and return 0 for success, -1 for failure.

int shutdown(int sockfd, int how);           \\ 关闭读端、写端或者读写端 成功返回0，失败返回-1。 sockfd:  accept 返回的描述符 how:           SHUT_RD    关闭读端       SHUT_WR    关闭写端       SHUT_RDWR  关闭读写端