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NOTE: This documentation is for version 0.1-alpha of nanomsg, but the latest released version is 1.1.5. Please see the documentation for 1.1.5 for the most up-to-date information.


#include <nanomsg/nn.h>

int nn_sendmsg (int s, const struct nn_msghdr *msghdr, int flags);


Sends data specified by msghdr paramter to socket s along with any additional control data. msghdr structure should be nullified before being used.

Structure nn_msghdr contains at least following members:

struct nn_iovec *msg_iov;
int msg_iovlen;
void *msg_control;
size_t msg_controllen;

msg_iov points to a scatter array of buffers to send. msg_iovlen specifies the size of the array.

msg_control points to the buffer containing control information to be associated with the message being sent. msg_controllen specifies the length of the buffer. If there’s no control information to send, msg_control should be set to NULL. For detailed discussion of how to set control data check nn_cmsg(3) man page.

Structure nn_iovec defines one element in the scatter array (i.e. a buffer to send to the socket) and contains following members:

void *iov_base;
size_t iov_len;

Alternatively, to send a buffer allocated by nn_allocmsg(3) function set iov_base to point to the pointer to the buffer and iov_len to NN_MSG constant. The buffer will be deallocated by nn_send function. Trying to deallocate it afterwards will result in undefined behaviour. Also, scatter array in nn_msghdr structure can contain only one element in this case.

To which of the peers will the message be sent to is determined by the particular socket type.

The flags argument is a combination of the flags defined below:


Specifies that the operation should be performed in non-blocking mode. If the message cannot be sent straight away, the function will fail with errno set to EAGAIN.


If the function succeeds number of bytes in the message is returned. Otherwise, negative number is returned and errno is set to to one of the values defined below.



The provided socket is invalid.


The operation is not supported by this socket type.


The operation cannot be performed on this socket at the moment because socket is not in the appropriate state. This error may occur with socket types that switch between several states.


Non-blocking mode was requested and the message cannot be sent at the moment.


The operation was interrupted by delivery of a signal before the message was sent.


Individual socket types may define their own specific timeouts. If such timeout is hit this error will be returned.


The library is terminating.


struct nn_msghdr hdr;
struct nn_iovec iov [2];
iov [0].iov_base = "Hello";
iov [0].iov_len = 5;
iov [1].iov_base = "World";
iov [1].iov_len = 5;
memset (&hdr, 0, sizeof (hdr));
hdr.msg_iov = iov;
hdr.msg_iovlen = 2;
nn_sendmsg (s, &hdr, 0);



Martin Sustrik <>

"nanomsg" is a trademark of Garrett D'Amore.