socket

#include <sys/socket.h>

int socket(int domain, int type, int protocol)

socket():

 (创建一个抽象的通讯端点socket，类似于file descriptor的概念，其目的用于对网络通讯的操作)

domain:

determines the nature of the communication ,including the address format(指明通讯的类型)

可选的参数如下：

AF_INETIPv4 Internet domain 

AF_INET6IPv6 Internet domain

AF_UNIXUNIXdomain (AF_LOCAL)

AF_UNSPECunspecified (AF_IPX)

type:

determines the type of the socket, which further determines the communication characteristics(SOCKET的类型)

可选的参数如下：

SOCK_DGRAMfixed-length, connectionless, unreliable messages

SOCK_RAWdatagram interface to IP

SOCK_SEQPACKETfixed-length, sequenced, reliable, connection-oriented messages 

SOCK_STREAMsequenced, reliable, bidirectional, connection-oriented byte streams

protocol:

select the default protocol for the given domain and socket type(和domain和type有关，一般都是指定为0)

return:

socket description, -1 on error