1.select函数

The select function returns the total number of socket handles that are ready and contained in the structures, zero if the time limit expired, or SOCKET_ERROR if an error occurred. If the return value is SOCKET_ERROR, can be used to retrieve a specific error code.

In summary, a socket will be identified in a particular set when select returns if:

readfds:

• If has been called and a connection is pending, will succeed.
• Data is available for reading (includes OOB data if SO_OOBINLINE is enabled).
• Connection has been closed/reset/terminated.

writefds:

• If processing a call (nonblocking), connection has succeeded.
• Data can be sent.

exceptfds:

• If processing a connect call (nonblocking), connection attempt failed.
• OOB data is available for reading (only if SO_OOBINLINE is disabled).

int select(  _In_    int                  nfds,  _Inout_ fd_set               *readfds,//检测可读性的  _Inout_ fd_set               *writefds,//检测可写性的  _Inout_ fd_set               *exceptfds,//检测存在错误的  _In_    const struct timeval *timeout   //select函数等待的最长时间,阻塞模式时设为0);

typedef struct fd_set {  u_int fd_count;  //集合中的数量  SOCKET fd_array[FD_SETSIZE];} fd_set; ....................