select

select is used by an application to receive notifications of events that occur on one or more sockets of interest.

Syntax

int select(
    __in int nfds,
    __inout fd_set *readfds,
    __inout fd_set *writefds,
    __inout fd_set *exceptfds,
    __in const struct timeval *timeout
);

Parameters

nfds

The nfds parameter is included only for compatibility with Berkeley sockets.

NOTE: select cannot monitor more than the MAX_SOCKET amount (64 sockets) per unique nfds. Attempts to monitor more than 64 sockets will result in an exception.

readfds

The address of the descriptor set that contains a set of sockets for which the application wishes to be notified when any of them becomes readable.

writefds

The address of the descriptor set that contains a set of sockets for which the application wishes to be notified when any of them becomes writeable.

exceptfds

The address of the descriptor set that contains a set of sockets for which the application wishes to be notified when any of them has a pending exception condition. The only exception condition that can create a notification is when out-of-band data is available on a socket.

timeout

The address of a struct timeval which specifies how long the application is willing to block on the select call while waiting for a notification..

Return Values

0 if a timeout occurs and none of the selected events has occurred on any of the selected sockets, or

A positive integer which is the sum of the number of sockets in each fd_set for which events have occurred, or

SOCKET_ERROR if the function fails

Use WSAGetLastError to retrieve a specific error code.

Remarks

An assumption cannot be made that the first socket descriptor returned to a particular thread or task in a system has the value 1, or that all socket descriptors created by a thread in a system will be incrementally increasing, beginning with 1.

If there are multiple threads in the system that creates sockets, then the value returned by socket must be treated essentially as a random positive integer.

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