常用類型的定義：
（以下定義從Winsock2.h文件中截取）
/*
?* The new type to be used in all
?* instances which refer to sockets.
?*/
typedef UINT_PTR??????? SOCKET;//SOCKET原來就是一個unsigned int的指針而已

/*
?* Select uses arrays of SOCKETs.? These macros manipulate such
?* arrays.? FD_SETSIZE may be defined by the user before including
?* this file, but the default here should be >= 64.
?*
?* CAVEAT IMPLEMENTOR and USER: THESE MACROS AND TYPES MUST BE
?* INCLUDED IN WINSOCK2.H EXACTLY AS SHOWN HERE.
?*/
#ifndef FD_SETSIZE
#define FD_SETSIZE????? 64
#endif /* FD_SETSIZE */
typedef struct fd_set {
??????? u_int fd_count;?????????????? /* how many are SET? */
??????? SOCKET? fd_array[FD_SETSIZE];?? /* an array of SOCKETs */
} fd_set;//fd_set是用來select的，表示一個集合，STL中不是有個模板類set么
//對fd_set結構，Winsock2.h中還定義了四個宏定義來操作fd_set
//FD_CLR(fd, set),FD_SET(fd, set),FD_ZERO(set),FD_ISSET(fd, set)
//一般用法是先定義一個fd_set,使用之前調用fd_zero，再將一個socket放到fd_set中
//經過一系列操作后，用fd_isset判斷某個socket是否還在set中。
//SOCKET fd;
//......
//fd_set ReadFds;
//FD_ZERO(&ReadFds);
//FD_SET(fd,&ReadFds);
//.....
//if ( FD_ISSET(fd,&ReadFds) )
//.....
/*
?* Structure used in select() call, taken from the BSD file sys/time.h.
?*/
struct timeval {
??????? long??? tv_sec;???????? /* seconds */
??????? long??? tv_usec;??????? /* and microseconds */
};//這個也是用于select函數中的，超時參數
struct? hostent {//表示主機的結構
??????? char??? FAR * h_name;?????????? /* official name of host */
??????? char??? FAR * FAR * h_aliases;? /* alias list */
??????? short?? h_addrtype;???????????? /* host address type */
??????? short?? h_length;?????????????? /* length of address */
??????? char??? FAR * FAR * h_addr_list; /* list of addresses */
#define h_addr? h_addr_list[0]????????? /* address, for backward compat */
};
/*
?* Internet address (old style... should be updated)//暈，什么時候update？
?*///原來每次看到in_addr結構都不知道為什么叫in_addr,原來是這樣。。。
struct in_addr {
??????? union {
??????????????? struct { u_char s_b1,s_b2,s_b3,s_b4; } S_un_b;
??????????????? struct { u_short s_w1,s_w2; } S_un_w;
??????????????? u_long S_addr; //大部分都用這個變量就夠了（一個ip地址32位剛好一個unsigned long）
??????? } S_un;
#define s_addr? S_un.S_addr //這樣定義以后用的很方便，in_addr.s_addr就可以了。
??????????????????????????????? /* can be used for most tcp & ip code */
#define s_host? S_un.S_un_b.s_b2
??????????????????????????????? /* host on imp */
#define s_net?? S_un.S_un_b.s_b1
??????????????????????????????? /* network */
#define s_imp?? S_un.S_un_w.s_w2
??????????????????????????????? /* imp */
#define s_impno S_un.S_un_b.s_b4
??????????????????????????????? /* imp # */
#define s_lh??? S_un.S_un_b.s_b3
??????????????????????????????? /* logical host */
};
//這b1，b2，b3，b4，w1，w2不知道有乜用，代表乜意思。。。
#endif
/*
?* Socket address, internet style.
?*/
struct sockaddr_in {
??????? short?? sin_family;//地址家族一般都是AF_INET或者PF_INET
??????? u_short sin_port;//端口
??????? struct? in_addr sin_addr;//ip地址
??????? char??? sin_zero[8];
};
/*
?* Structure used by kernel to store most//計算機內核中處理用的是這種表示
?* addresses.
?*/
struct sockaddr {
??????? u_short sa_family;????????????? /* address family */
??????? char??? sa_data[14];??????????? /* up to 14 bytes of direct address */
};
//仔細算一下sockaddr_in和sockaddr兩個結構的大小是一樣，所以可以直接強制類型轉換賦值
//比如accept函數其中一個參數類型struct sockaddr FAR * ，你如果有一個struct sockaddr_in myaddr
//就可以直接accept(..(struct sockaddr *)myaddr.....
/*
?* WinSock 2 extension -- WSABUF and QOS struct, include qos.h
?* to pull in FLOWSPEC and related definitions
?*/
typedef struct _WSABUF {//緩沖區，一般ms在帶WSA前綴的accept，receive，send等函數中才用到
??? u_long????? len;???? /* the length of the buffer */
??? char FAR *? buf;???? /* the pointer to the buffer */
} WSABUF, FAR * LPWSABUF;
typedef struct WSAData {
??????? WORD??????????????????? wVersion;
??????? WORD??????????????????? wHighVersion;
#ifdef _WIN64
??????? unsigned short????????? iMaxSockets;
??????? unsigned short????????? iMaxUdpDg;
??????? char FAR *????????????? lpVendorInfo;
??????? char??????????????????? szDescription[WSADESCRIPTION_LEN+1];
??????? char??????????????????? szSystemStatus[WSASYS_STATUS_LEN+1];
#else
??????? char??????????????????? szDescription[WSADESCRIPTION_LEN+1];
??????? char??????????????????? szSystemStatus[WSASYS_STATUS_LEN+1];
??????? unsigned short????????? iMaxSockets;
??????? unsigned short????????? iMaxUdpDg;
??????? char FAR *????????????? lpVendorInfo;
#endif
} WSADATA, FAR * LPWSADATA;//其實這個結構不需要怎么了解，因為它在用的很少，就是在調用WSAStartup才用到一次

/*
?* Address families.
?*/
#define AF_UNSPEC?????? 0?????????????? /* unspecified */
/*
?* Although? AF_UNSPEC? is? defined for backwards compatibility, using
?* AF_UNSPEC for the "af" parameter when creating a socket is STRONGLY
?* DISCOURAGED.??? The? interpretation? of? the? "protocol"? parameter
?* depends? on the actual address family chosen.? As environments grow
?* to? include? more? and? more? address families that use overlapping
?* protocol? values? there? is? more? and? more? chance of choosing an
?* undesired address family when AF_UNSPEC is used.
?*/
#define AF_UNIX???????? 1?????????????? /* local to host (pipes, portals) */
#define AF_INET???????? 2?????????????? /* internetwork: UDP, TCP, etc. */
#define AF_IMPLINK????? 3?????????????? /* arpanet imp addresses */
#define AF_PUP????????? 4?????????????? /* pup protocols: e.g. BSP */
#define AF_CHAOS??????? 5?????????????? /* mit CHAOS protocols */
#define AF_NS?????????? 6?????????????? /* XEROX NS protocols */
#define AF_IPX????????? AF_NS?????????? /* IPX protocols: IPX, SPX, etc. */
#define AF_ISO????????? 7?????????????? /* ISO protocols */
#define AF_OSI????????? AF_ISO????????? /* OSI is ISO */
#define AF_ECMA???????? 8?????????????? /* european computer manufacturers */
#define AF_DATAKIT????? 9?????????????? /* datakit protocols */
#define AF_CCITT??????? 10????????????? /* CCITT protocols, X.25 etc */
#define AF_SNA????????? 11????????????? /* IBM SNA */
#define AF_DECnet?????? 12????????????? /* DECnet */
#define AF_DLI????????? 13????????????? /* Direct data link interface */
#define AF_LAT????????? 14????????????? /* LAT */
#define AF_HYLINK?????? 15????????????? /* NSC Hyperchannel */
#define AF_APPLETALK??? 16????????????? /* AppleTalk */
#define AF_NETBIOS????? 17????????????? /* NetBios-style addresses */
#define AF_VOICEVIEW??? 18????????????? /* VoiceView */
#define AF_FIREFOX????? 19????????????? /* Protocols from Firefox */
#define AF_UNKNOWN1???? 20????????????? /* Somebody is using this! */
#define AF_BAN????????? 21????????????? /* Banyan */
#define AF_ATM????????? 22????????????? /* Native ATM Services */
#define AF_INET6??????? 23????????????? /* Internetwork Version 6 */
#define AF_CLUSTER????? 24????????????? /* Microsoft Wolfpack */
#define AF_12844??????? 25????????????? /* IEEE 1284.4 WG AF */
#define AF_IRDA???????? 26????????????? /* IrDA */
#define AF_NETDES?????? 28????????????? /* Network Designers OSI & gateway
?????????????????????????????????????????? enabled protocols */
#define AF_TCNPROCESS?? 29
#define AF_TCNMESSAGE?? 30
#define AF_ICLFXBM????? 31

#define AF_MAX????????? 32

/*
?* Protocol families, same as address families for now.
?*/
#define PF_UNSPEC?????? AF_UNSPEC
#define PF_UNIX???????? AF_UNIX
#define PF_INET???????? AF_INET
#define PF_IMPLINK????? AF_IMPLINK
#define PF_PUP????????? AF_PUP
#define PF_CHAOS??????? AF_CHAOS
#define PF_NS?????????? AF_NS
#define PF_IPX????????? AF_IPX
#define PF_ISO????????? AF_ISO
#define PF_OSI????????? AF_OSI
#define PF_ECMA???????? AF_ECMA
#define PF_DATAKIT????? AF_DATAKIT
#define PF_CCITT??????? AF_CCITT
#define PF_SNA????????? AF_SNA
#define PF_DECnet?????? AF_DECnet
#define PF_DLI????????? AF_DLI
#define PF_LAT????????? AF_LAT
#define PF_HYLINK?????? AF_HYLINK
#define PF_APPLETALK??? AF_APPLETALK
#define PF_VOICEVIEW??? AF_VOICEVIEW
#define PF_FIREFOX????? AF_FIREFOX
#define PF_UNKNOWN1???? AF_UNKNOWN1
#define PF_BAN????????? AF_BAN
#define PF_ATM????????? AF_ATM
#define PF_INET6??????? AF_INET6

#define PF_MAX????????? AF_MAX

下面這些函數屬于基本常用函數，下次學習
u_long htonl(u_long hostlong)
u_short htons(u_short hostshort)
u_long ntohl(u_long netlong)
u_short ntohs(u_short netshort)
unsigned long inet_addr(const char* cp);
int getpeername(SOCKET s,struct sockaddr* name,int* namelen);
int getsockname(SOCKET s,struct sockaddr* name,int* namelen);
char* FAR inet_ntoa(struct in_addr in);
struct HOSTENT* FAR gethostbyaddr(const char* addr,int len,int type);
struct hostent* FAR gethostbyname(const char* name);
int gethostname(char* name,int namelen);
int WSAGetLastError(void);
int WSAStartup(WORD wVersionRequested,LPWSADATA lpWSAData);
int ioctlsocket(SOCKET s,long cmd,u_long* argp);
int listen(SOCKET s,int backlog);
SOCKET accept(SOCKET s,struct sockaddr* addr,int* addrlen);
int send(SOCKET s,const char* buf,int len,int flags);
int recv(SOCKET s,char* buf,int len,int flags);

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