Please note that as of October 24, 2014, the Nokia Developer Wiki will no longer be accepting user contributions, including new entries, edits and comments, as we begin transitioning to our new home, in the Windows Phone Development Wiki. We plan to move over the majority of the existing entries. Thanks for all your past and future contributions.

Open C Sockets: recv, recvfrom, recvmsg methods

From Wiki
Jump to: navigation, search
Article Metadata
Created: polaka_sr (17 Jun 2008)
Last edited: hamishwillee (27 Jul 2012)

The recv, recvfrom, recvmsg methods helps in receiving a message from a socket.

ssize_t recv (int s, void *buf, size_t len, int flags);
ssize_t recvfrom (int s, void * restrict buf, size_t len, int flags,
struct sockaddr * restrict from, socklen_t * restrict fromlen);
ssize_t recvmsg (int s, struct msghdr *msg, int flags);

The recvfrom and recvmsg system calls are used to receive messages from a socket, and may be used to receive data on a socket whether or not it is connection-oriented. The recv function is normally used only on a connected socket (see connect and is identical to recvfrom with a null pointer passed as its from argument. All three routines return the length of the message on successful completion.

The recvmsg system call uses a msghdr structure to minimize the number of directly supplied arguments. This structure has the following form, as defined in sys/socket.h:

struct msghdr {
caddr_t msg_name; /* optional address */
u_int msg_namelen; /* size of address */
struct iovec *msg_iov; /* scatter/gather array */
u_int msg_iovlen; /* # elements in msg_iov */
caddr_t msg_control; /* ancillary data, see below */
u_int msg_controllen; /* ancillary data buffer len */
int msg_flags; /* flags on received message */

And following code snippets shows the usage of recv, recvfrom, recvmsg functions:

#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
void Recv()
struct sockaddr_in serv_addr;
int sock_fd;
char line[10];
int size = 10;
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
serv_addr.sin_port = htons(5000);
connect(sock_fd,(struct sockaddr*)&serv_addr,sizeof(serv_addr));
recv(sock_fd, line, size, 0);

#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
void Sendto()
struct sockaddr_in sender_addr;
int sock_fd;
char line[15] = "Hello World!";
unsigned int size = sizeof(sender_addr);
sender_addr.sin_family = AF_INET;
sender_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
sender_addr.sin_port = htons(5000);
recvfrom(sock_fd,line,13,0,(struct sockaddr*)&sender_addr,&size);

#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
void SendMsgRecvMsg()
int sock_fd;
unsigned int sender_len;
struct msghdr msg;
struct iovec iov;
struct sockaddr_in receiver_addr,sender_addr;
char line[10];
receiver_addr.sin_family = AF_INET;
receiver_addr.sin_addr.s_addr = htonl(INADDR_ANY);
receiver_addr.sin_port = htons(5000);
bind(sock_fd,(struct sockaddr*)&receiver_addr,sizeof(receiver_addr));
sender_len = sizeof(sender_addr);
msg.msg_name = &sender_addr;
msg.msg_namelen = sender_len;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_iov->iov_base = line;
msg.msg_iov->iov_len = 10;
msg.msg_control = 0;
msg.msg_controllen = 0;
msg.msg_flags = 0;

These calls return the number of bytes received, or -1 if an error occurred.

Wiki Links

Open C Sockets Overview

This page was last modified on 27 July 2012, at 04:18.
225 page views in the last 30 days.