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recv(2) System Calls Manual recv(2) NAME recv - Receives messages from connected sockets SYNOPSIS #include <sys/socket.h> ssize_t recv ( int socket, void *buffer, size_t length, int flags ); [Digital] The following definition of the recv() function does not conform to current standards and is supported only for backward compat- ibility (see standards(5)): #include <sys/socket.h> int recv ( int socket, char *buffer, int length, int flags ); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: recv(): XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Specifies the socket descriptor. Points to a buffer where the message should be placed. Specifies the size of the buffer pointed to by the buffer parameter. Points to a value controlling the message reception. The flags parameter is formed by logically ORing one or more of the following values, defined in the sys/socket.h file: Peek at incoming message. The data is treated as unread and the next recv() function (or similar function) will still return this data. Process out-of-band data. Requests that the function block wait until the full amount of data requested can be returned. The function may return a smaller amount of data if a signal is caught, the connection is terminated, or an error is pending for the socket. DESCRIPTION The recv() function receives messages from a connected socket. The recvfrom() and recvmsg() functions receive messages from both connected and unconnected sockets; however, they are usually used for unconnected sockets only. The recv() function returns the length of the message. If a message is too long to fit in the supplied buffer, excess bytes may be truncated depending on the type of socket that issued the message. If no messages are available at the socket, the recv() function waits for a message to arrive, unless the socket is nonblocking. If a socket is nonblocking, errno is set to [EWOULDBLOCK]. Use the select() function to determine when more data arrives. NOTES [Digital] The recv() function is identical to the recvfrom() function with a zero-valued address_len parameter, and to the read() function if no flags are used. For that reason the recv() 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 recv() function returns the length of the message in bytes. Otherwise, a value of -1 is returned, and errno is set to indicate the error. ERRORS If the recv() 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 data was directed to be received into a nonexis- tent or protected part of the process address space. The buffer para- meter is invalid. A signal interrupted the recv() function before any data was available. The MSG_OOB flag is set and no out-of-band data is available. Receive is attempted on a connection-oriented socket that is not con- nected. The socket parameter refers to a file, not a socket. The specified flags are not supported for this socket type or protocol. The connection timed out during connection establishment or due to a transmission timeout on active connection. The socket is marked non- blocking, and no data is waiting to be received. RELATED INFORMATION Functions: recvfrom(2), recvmsg(2), send(2), sendmsg(2), sendto(2), se- lect(2), shutdown(2), socket(2), read(2), write(2) Standards: standards(5) delim off recv(2)