connect (2)

An electrical connector is an electromechanical device used to join electrical conductors and create an electrical circuit. Most electrical connectors have a gender – i.e. the male component, called a plug, connects to the female component, or socket. An adapter can be used to join dissimilar connectors.

Chassis /'ʃæsi:/ or panel connectors are permanently attached to a piece of equipment so users can connect a cable to a stationary device.

The connect() system call connects the socket referred to by the file descriptor sockfd to the address specified by addr. The addrlen argument specifies the size of addr. The format of the address in addr is determined by the address space of the socket sockfd; "man 2 socket" for further details. man是manual的缩写。

If the socket sockfd is of type SOCK_DGRAM, then addr is the address to which datagrams are sent by default, and the only address from which datagrams are received. UDP也是可以connect的。If the socket is of type SOCK_STREAM or SOCK_SEQPACKET, this call attempts to make a connection to the socket that is bound to the address specified by addr.

Some protocol sockets (e.g., UNIX domain stream sockets) may successfully connect() only once.

Some protocol sockets (e.g., datagram sockets in the UNIX and Internet domains) may use connect() multiple times to change their association.

Some protocol sockets (e.g., TCP sockets as well as datagram sockets in the UNIX and Internet domains) may dissolve the association by connecting to an address with the sa_family member of sockaddr set to AF_UNSPEC; thereafter, the socket can be connected to another address.

If the connection or binding succeeds, zero is returned. On error, -1 is returned, and errno is set to indicate the error. "man perror"

• EAGAIN: For nonblocking UNIX domain sockets, the socket is nonblocking, and the connection cannot be completed immediately. For other socket families, there are insufficient entries in the routing cache.
• EALREADY: The socket is nonblocking and a previous connection attempt has not yet been completed.
• EINPROGRESS: The socket is nonblocking and the connection cannot be completed immediately. (UNIX domain sockets failed with EAGAIN instead.) It is possible to select(2) or poll(2) for completion by selecting the socket for writing. After select(2) indicates writability, use getsockopt(2) to read the SO_ERROR option at level SOL_SOCKET to determine whether connect() completed successfully (SO_ERROR is zero) or unsuccessfully (SO_ERROR is one of the usual error codes listed here, explaining the reason for the failure).
• EINTR: The system call was interrupted by a signal that was caught; "man 7 signal".
• ...

If connect() fails, consider the state of the socket as unspecified. Portable applications should close the socket and create a new one for reconnecting.

An example of the use of connect() is shown in "man 3 getaddrinfo".

六级/考研单词: gender, component, plug, socket, perpetual, equip, farther, default, bind, protocol, domain, multiple, dissolve, nil, poll, interrupt