Go to the previous, next section.

Accepting Connections

When a server receives a connection request, it can complete the connection by accepting the request. Use the function accept to do this.

A socket that has been established as a server can accept connection requests from multiple clients. The server's original socket does not become part of the connection; instead, accept makes a new socket which participates in the connection. accept returns the descriptor for this socket. The server's original socket remains available for listening for further connection requests.

The number of pending connection requests on a server socket is finite. If connection requests arrive from clients faster than the server can act upon them, the queue can fill up and additional requests are refused with a ECONNREFUSED error. You can specify the maximum length of this queue as an argument to the listen function, although the system may also impose its own internal limit on the length of this queue.

Function: int accept (int socket, struct sockaddr *addr, size_t *length_ptr)

This function is used to accept a connection request on the server socket socket.

The accept function waits if there are no connections pending, unless the socket socket has nonblocking mode set. (You can use select to wait for a pending connection, with a nonblocking socket.) See section File Status Flags, for information about nonblocking mode.

The addr and length_ptr arguments are used to return information about the name of the client socket that initiated the connection. See section Socket Addresses, for information about the format of the information.

Accepting a connection does not make socket part of the connection. Instead, it creates a new socket which becomes connected. The normal return value of accept is the file descriptor for the new socket.

After accept, the original socket socket remains open and unconnected, and continues listening until you close it. You can accept further connections with socket by calling accept again.

If an error occurs, accept returns -1. The following errno error conditions are defined for this function:

The socket argument is not a valid file descriptor.

The descriptor socket argument is not a socket.

The descriptor socket does not support this operation.

socket has nonblocking mode set, and there are no pending connections immediately available.

The accept function is not allowed for sockets using connectionless communication styles.

Go to the previous, next section.