Receive multiple messages and their headers from a socket


#include <sys/types.h>
#include <sys/socket.h>

int recvmmsg( int s,
              struct mmsghdr *mmsg,
              unsigned int vlen,
              unsigned int flags,
              struct timespec *timeout );


The descriptor for the socket; see socket().
A pointer to an array of mmsghdr structures where the function can store the message headers; see below.
The length of the mmsg array; limited to 1024 elements.
A bitwise OR of zero or more of the following:
  • MSG_OOB — process out-of-band data. This flag requests receipt of out-of-band data that wouldn't be received in the normal data stream. You can't use this flag with protocols that place expedited data at the head of the normal data queue.
  • MSG_PEEK — peek at the incoming message. This flag causes the receive operation to return data from the beginning of the receive queue without removing that data from the queue. Thus, a subsequent receive call will return the same data.
  • MSG_WAITALL — wait for full request or error. This flag requests that the operation block until the full request is satisfied. But the call may still return less data than requested if a signal is caught, if an error or disconnect occurs, or if the next data to be received is of a different type than that returned.
The length of time to wait for messages to be received, after which recvmmsg() returns.



Use the -l socket option to qcc to link against this library.


The recvmmsg() function receives multiple messages from a socket, s, whether or not it's connection-oriented.

The recvmmsg() function uses a mmsghdr structure to minimize the number of directly supplied parameters. This structure is defined in <sys/socket.h> as follows:

struct mmsghdr {
    struct msghdr   msg_hdr; /* the message to be sent */
    unsigned int    msg_len; /* number of bytes transmitted */

The msg_len member contains the number of bytes sent for each msg_hdr member. The array has vlen elements, but if there's an error, a number fewer than vlen may be returned. For a description of the msghdr structure, see recvmsg().


The number of messages received, or -1 if an error occurs (errno is set).


Not enough memory.
An attempt was made to receive an amount of data that exceeds the allowable limit.



Cancellation point Yes
Interrupt handler No
Signal handler No
Thread Yes