nn_send - Man Page

send a message


#include <nanomsg/nn.h>

int nn_send (int s, const void *buf, size_t len, int flags);


The function will send a message containing the data from buffer pointed to by buf parameter to the socket s. The message will be len bytes long.

Alternatively, to send a buffer allocated by nn_allocmsg(3) function set the buf parameter to point to the pointer to the buffer and len parameter to NN_MSG constant. In this case a successful call to nn_send will deallocate the buffer. Trying to deallocate it afterwards will result in undefined behaviour.

Which of the peers the message will 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.

Return Value

If the function succeeds, the number of bytes in the message is returned. Otherwise, -1 is returned and errno is set to to one of the values defined below.



buf is NULL or len is NN_MSG and the message pointer (pointed to by buf) is NULL.


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 the 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.


Using data directly:

nbytes = nn_send (s, "ABC", 3, 0);
assert (nbytes == 3);

Using a pre-allocated message buffer:

void *msg = nn_allocmsg(3, 0);
strncpy(msg, "ABC", 3);
nbytes = nn_send (s, &msg, NN_MSG, 0);
assert (nbytes == 3);

See Also

nn_recv(3) nn_sendmsg(3) nn_socket(3) nanomsg(7)


Martin Sustrik

Referenced By

nanomsg(7), nn_allocmsg(3), nn_pair(7), nn_recv(3), nn_sendmsg(3), nn_term(3).

2024-01-25 nanomsg 1.1.5