基于select的socket编程

1.select函数

The select function returns the total number of socket handles that are ready and contained in the fd_set structures, zero if the time limit expired, or SOCKET_ERROR if an error occurred. If the return value is SOCKET_ERROR, WSAGetLastError 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 listen has been called and a connection is pending, accept 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 connect 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;




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