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send(2) System Calls Manual send(2) NAME send - Sends messages on a socket SYNOPSIS #include <sys/socket.h> ssize_t send ( int socket, const void *buffer, size_t length, int flags ); [Digital] The following definition of the send() function does not conform to current standards and is supported only for backward compat- ibility (see standards(5)): int send ( int socket, char *message, int length, int flags ); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: send(): XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Specifies the unique name for the socket. Points to the buffer con- taining the message to send. Specifies the length of the message in bytes. Allows the sender to control the transmission of the message. The flags parameter to send a call is formed by logically ORing the values shown in the following list, defined in the sys/socket.h header file: Sends out-of-band data on sockets that support out-of-band commu- nication. Sends without using routing tables. (Not recommended, for debugging purposes only.) DESCRIPTION The send() function sends a message only when the socket is connected. The sendto() and sendmsg() functions can be used with unconnected or connected sockets. Specify the length of the message with the length parameter. If the message is too long to pass through the underlying protocol, the system returns an error and does not transmit the message. No indication of failure to deliver is implied in a send() function. A return value of -1 indicates only locally detected errors. If no space for messages is available at the sending socket to hold the message to be transmitted, the send() function blocks unless the socket is in a nonblocking I/O mode. Use the select() function to determine when it is possible to send more data. NOTES [Digital] The send() function is identical to the sendto() function with a zero-valued dest_len parameter, and to the write() function if no flags are used. For that reason, the send() function is disabled when 4.4BSD behavior is enabled (that is, when the _SOCKADDR_LEN com- pile-time option is defined). RETURN VALUES Upon successful completion, the send() function returns the number of characters sent. Otherwise, a value of -1 is returned and errno is set to indicate the error. ERRORS If the send() function fails, errno may be set to one of the following values: The socket parameter is not valid. A connection was forcibly closed by a peer. The socket is not connection-oriented and no peer address is set. The message parameter is not in a readable or writable part of the user address space. A signal interrupted send before any data was transmitted. The message is too large to be sent all at once, as the socket requires. The socket is not connected or otherwise has not had the peer prespecified. The socket parameter refers to a file, not a socket. The socket argument is associated with a socket that does not support one or more of the values set in flags. The socket is shut down for writing, or the socket is connection-oriented and the peer is closed or shut down for reading. In the latter case, and if the socket is of type SOCK_STREAM, the SIGPIPE signal is generated to the calling process. The socket is marked nonblocking, and no space is available for the send() function. RELATED INFORMATION Functions: recv(2), recvfrom(2), recvmsg(2), sendmsg(2), sendto(2), shutdown(2), connect(2), socket(2), getsockopt(2), select(2), setsock- opt(2) Standards: standards(5) delim off send(2)